Dissertations / Theses on the topic 'Soil and Water Sciences'

The present work is a contribution to description and understanding of the distribution and movement of water in swelling soils. In order to investigate the moisture distribution in swelling soils a detailed knowledge of volume change properties, flow characteristics and total potential of water in the soil is essential. Therefore, a possible volume change mechanism is first described by dividing the swelling soils into four categories and volume change of a swelling soil is measured under different overburden pressures. The measured and calculated (from volume change data) overburden potential components are used to check the validity of the derivation of a load factor, ∝. Moisture diffusivity in swelling soil under different overburden pressures is measured using Gardner's (1956) outflow method. Behaviour of equilibrium moisture profiles in swelling soils is theoretically explained, solving the differential equation by considering the physical variation of individual soil properties with moisture content and overburden pressure. Using the measured volume change data and moisture potentials under various overburden pressures, the behaviour of possible moisture profiles are described at equilibrium and under steady vertical flows in swelling soils. It is shown that high overburden pressures lead to soil water behaviour quite different from any previously reported.

Efforts to manage eutrophication of surface waters should recognize that macropore flow transports significantly more phosphorus (P) to surface waters via tile drains than water that percolates through the soil matrix. For the watershed-scale SWAT (Soil and Water Assessment Tool) model to describe phosphorus transport through tile drains, SWAT needs to partition percolation into macropore flow and matrix flow. The objective of this study was to evaluate the effects of a new macropore flow algorithm on the partitioning of hydrological flows, using input data that are readily available, consistent with the current approach to SWAT modeling. The algorithm was evaluated in a proof of concept outside of SWAT and within a re-conceptualized version, SWAT-QC2. The proof of concept reproduced episodic macropore flows, which increased with greater daily rainfall if infiltration exceeded a threshold that was lower for finer-textured soils. Although the algorithm did not improve predictions of streamflow of an agricultural subwatershed in southern Quebec (30 km2), the algorithm improved SWAT's partitioning between surface runoff and subsurface flow. SWAT-QC2 also predicted reasonably the separation between macropore and matrix components of subsurface flow, upon comparison with results from a chemical-based hydrograph separation of the subwatershed's streamflow. As in the proof of concept, the predicted amount of macropore flow into tile drains was greater under finer-textured soils than coarser-textured soils. By describing the portion of percolation that flows through macropores and potentially controls subsurface P transport, the macropore flow algorithm provides a framework for future developments of SWAT that describe macropore transport of P to tile drains. To improve the partitioning between macropore and matrix flows, future developments of SWAT-QC2 should account for dynamic macropore connectivity and the effects of soil moisture on macropore flow, but more research is needed to determine experimentally the spatiotemporal variation of macropore flow in agricultural soils.
Les stratégies d'intervention ciblées sur la prévention de l'eutrophisation des eaux de surface en milieu agricole devraient prendre en compte que relativement plus de phosphore chemine vers les drains souterrains par les macropores du sol qu'en cheminement matriciel. Afin de décrire les phénomènes de transport de phosphore aux drains, le modèle hydrologique SWAT (Soil and Water Assessment Tool) doit être en mesure de distinguer ces processus de transfert. La présente étude avait pour objectif d'évaluer la performance d'un nouvel algorithme séparant les écoulements matriciels et préférentiels, en mettant à profit des jeux de données existantes et suivant une démarche compatible avec l'approche de modélisation inhérente à SWAT. L'algorithme a d'abord profité d'une validation conceptuelle, hors du modèle SWAT, puis d'une évaluation suivant son intégration à une nouvelle version du modèle hydrologique, SWAT-QC2. La validation conceptuelle de l'algorithme a démontré que les flux matriciels épisodiques prédits augmentent avec les précipitations journalières, à la condition que le taux d'infiltration ait atteint un seuil limite, relativement moins élevé en sol argileux. Bien que l'algorithme n'ait pas amélioré la prédiction du débit total d'un petit bassin versant du Sud du Québec (30 km2), il a néanmoins amélioré la performance du modèle SWAT à répartir les écoulements de surface et souterrains. La comparaison des prédictions du modèle hydrologique avec les résultats de séparation des hydrogrammes à l'exutoire du même bassin versant suivant une méthode chimique témoigne d'une performance réaliste de SWAT-QC2 à prédire la répartition des flux souterrains préférentiels et matriciels. A l'instar de la validation conceptuelle de l'algorithme, les flux préférentiels prédits sont relativement plus importants en sol argileux qu'en texture plus grossière. En décrivant la proportion des écoulements souterrains qui emprunte la voie préférentielle, et qui contrôle potentiellement les transferts souterrains de P, l'algorithme d'écoulement en macropores constitue une assise pour le développement ultérieur de SWAT intégrant une description des transferts souterrains de phosphore vers les drains souterrains. Afin d'améliorer la performance de SWAT-QC2 à séparer les flux préférentiels et matriciels, les développements futurs du modèle hydrologique devraient prendre en compte la nature dynamique de la connectivité des macropores, de même que les effets de l'humidité du sol sur l'écoulement préférentiel. Cette démarche appelle cependant à une meilleure caractérisation expérimentale de la variabilité spatio-temporelle des flux préférentiels en sols agricoles.

Cover crops and crop residue play a multifunctional role in improving soil hydrological properties, soil water storage and water use efficiency (WUE). This study was conducted to better understand the role of crop residue and cover crop on soil properties and soil water dynamics. The study was conducted at the USDA-ARS North Central Agricultural Research Laboratory, located in Brookings, South Dakota. Two residue removal treatments that include low residue removal (LRR) and high residue removal (HRR) were established in 2000 with randomized complete block design under no-till corn (Zea mays L.) and soybean (Glycine max L.) rotation. In 2005, cover crop treatments which include cover crops (CC) and no cover crops (NCC) were integrated into the overall design. Soil samples were collected in 2014, 2015 and 2016. Data from this study showed that LRR treatment resulted in lower bulk density (BD) by 7 and 9% compared to HRR in 2015 and 2016, respectively, for 0-5 cm depth. Similarly, LRR treatment significantly reduced soil penetration resistance (SPR) by 25% in 0-5 cm depth compared with HRR treatment. In addition to this, LRR treatment significantly increased soil organic carbon (SOC) concentrations and total nitrogen (TN) by 22 and 17%, respectively, in 0-5 cm. Similarly, CC treatment resulted in lower BD and SPR by 7% and 23%, respectively, in 0-5 cm depth in 2015 compared with NCC treatment. The LRR significantly increased soil water infiltration by 66 and 22% compared to HRR in 2014 and 2015, respectively. Similarly, the CC treatment significantly increased infiltration by 82 and 22% compared to the NCC in 2014 and 2015, respectively. The significant impact of a crop residue was observed on soil water retention (SWR) in 2014 and 2015 for the 0-5 cm depth. The LRR and CC treatments increased the soil volumetric moisture content (VMC) and soil water storage (SWS) on the surface 0-5 cm depth. However, the trend was not always significant during the growing season. The CC treatment significantly impacted the soybean yield by 14% and WUE by 13% compared with NCC treatment. Some interaction of residue by cover crops was observed on BD, SPR, VMC, and SWS, which showed that the use of cover crops with LRR can be beneficial in improving the soil properties.

Eleven series of replicated tests were conducted using 38.1 mm, 15.9 mm, and 9.5 mm gravel to determine the most effective soil surface cover to prevent soil erosion from rainfall. A sediment tray one meter square in size with an integrated rainfall simulator was used to generate data after initial trial runs had established test procedures. Various size gravels and a control with no cover were tested in a laboratory using simulated rainfall to evaluate their effectiveness in preventing erosion. Through thirty-three experiments, signature traits of specific rock sizes were identified. Experiments on 38.1 mm gravel indicated the usefulness of rock mulches in soil erosion prevention. Evaluations with 9.5 mm material indicated that erosion prevention varies inversely with particle size. Experiments with 15.9 mm gravel suggested that this material could increase erosion. This study reflects the ambivalence in the literature and points to the complexity of micro-interactions and erosion potential as influenced by gravel size. Six mechanisms governing rock mulch erosion were proposed.

Agricultural system models integrate many different processes that cannot all be measured in field experiments and help quantify soil water dynamics, crop evapotranspiration, and crop growth with high temporal resolution. Understanding soil water dynamics and crop evapotranspiration is essential to improve agricultural management of field crops. For example, the interaction between nitrogen application rate and water dynamics is not sufficiently understood. In most cases, model simulations deviate from field measurements, especially when model input parameters are indirectly and unspecifically derived. The extent to which measured soil hydraulic property inputs decrease the discrepancy between measured and simulated soil water status is not well understood. Consequently, this study: (i) investigated thr use of measured soil hydraulic properties as Root Zone Water Quality Model (RZWQM2) inputs compared to indirectly derived inputs; (ii) explored the capability of calibrating measured soil hydraulic property input parameters for one crop and using them for other crops without further calibration; (iii) studied the effect of the nitrogen application rate on the behavior of soil water dynamics and crop evapotranspiration using RZWQM2 under different rainfall amounts. To evaluate the model in different field management conditions, a field experiment with soybean, corn, wheat, and fallow soil was conducted from 2015 – 2017 to collect field data to calibrate and validate the RZWQM2 model. The model presented a satisfactory response to using measured soil hydraulic property inputs and a satisfactory capability to quantify the effect of nitrogen rates on daily crop evapotranspiration, soil water dynamics, and crop growth. With sufficient measurements of soil hydraulic parameters, it was possible to build a RZWQM2 model that produced reasonable results even without calibration.

Off-site soil erosion has tremendous impacts on the present state of most river systems throughout the United States, contributing sediments to channels mainly as nonpoint pollution resulting from land-use and agricultural practices and leading to sedimentation downstream and downwind, a decrease in the transport capacity of streams, increase in the risk of flooding, filling reservoirs, and eutrophication. A primary focus in examining the problems associated with soil erosion arid ultimately in proposing control measures should be on identifying the sources of the sediment. Therefore, a model that would be able to assess soil erosion needs to start by identifying the sediment sources and delivery paths to channels, link these sediment supply processes to in-channel sediment transport and storage and ultimately to basin sediment yield. This study focuses on the Upper Green River Basin in Kentucky and is concerned with analyzing hillslope erosion rates using The Unit Stream Power Erosion and Deposition soil erosion model (Mitas and Mitasova, 1996) and GIS, and thereby estimating patterns of sediment supply to rivers in order to predict which portions of the channel network are more likely to store large amounts of fine sediments. Results indicate that much of the eroded sediments are redistributed within the hillslope system, but also that a large proportion is delivered to the channel. These predictions have been tested by sampling the fine sediment content of the streambed at key locations along the channel network and comparing the observed patterns to those predicted by the soil erosion model. By linking topographic and soil characteristics with land cover data, it has been concluded that high intensity erosion tends to occur at contact between different vegetation covers, on barren lands and croplands, and 15-25% slopes poorly protected by vegetation. Erosion ""hot spots"" have been identified in the Pitman Creek HUC 05110001-90-130 and 05110001-90-050, both part of the Big Pitman Creek sub-basin, as well as in Mill and Falling Timber Creeks with lower intensity.

The success of wetland restoration projects depends in part on the length of time that a soil is in a reduced redox state. The length of time that a soil is reduced depends on how quickly reduction occurs following saturation with water. The relationship between reduction rate and various soil chemical and mineralogical properties is poorly understood, but such properties might be manipulated to improve the success of wetland restoration projects. The goals of this research were to determine soil properties that predict the rate at which soils undergo reduction when saturated, and to determine the roles of electron donors and acceptors on reduction rates. Sixteen soil samples were collected at various depths from two wetland sites, a Carolina bay (Juniper Bay) and a wetland catena (Frog Level). Soils were incubated in specially designed redox incubators to monitor reduction rates, changes in soil properties, and soil solution chemistry. Soil samples were subjected to three cycles of oxidation and reduction during the course of 36 d. Soil reduction rates were determined from the slopes of linear regression models fit to data for redox potential (Eh) over time. Reduction rates varied among soils from 1.2 to 46.2 mV h-1, and were significantly greater (p-value < 0.05) for soils with total organic carbon (TOC) > 10 g kg-1 than in soils with TOC < 10 g kg-1. Increasing amounts of dissolved Fe(II) were found at Eh values below 500 mV for pH between 4.5 and 5.1. Mineral soils with total reduction rates > 10 mV h-1 released significantly more Fe(II) into solution than mineral soils with reduction rates < 10 mV h-1 (p-value < 0.05). Regression results indicated that organic carbon, an electron donor, was the dominant factor controlling reduction rates up to 10 mV h-1, and an electron acceptor Fe(III) was the dominant factor controlling reduction rates > 10 mV h-1. For wetland restoration purposes multiple linear regression models based on our results that include TOC concentration and pH can be used along with hydrologic data to predict reduction rates in saturated soils.

The previously developed watershed hydrological and water quality model for St. Louis Bay watershed by Kieffer (2002) was refined and calibrated. The aspects of model development refinement included development of fertilization-related nutrient input parameters, evaluation of nutrient input methods, development of plant uptake-related nutrient input parameters, non-cropland simulation using PQUAL module, and recalibration of hydrology in Jourdan River. The related information of typical cropland management practice based on consultation from Mississippi State University Extention Service personnel was integrated into the watershed model. In addition, the Mississippi Department of Environmental Quality (MDEQ) observed water quality data were analyzed to evaluate the appropriateness of current watershed delineation and assess the health of the stream based on the MDEQ proposed numerical water quality target. The refined watershed model was calibrated in Wolf Rover and Jourdan River using both USGS and MDEQ observed water quality data. The concentrations of water quality constituents calculated from the developed watershed model will be provided as boundary conditions for the developed Bay hydrodynamic and water quality model for Total Maximum Daily Load studies.

When plants and animals die they are decomposed into microscopic particles of organic carbon. In the ground, these carbon particles are dissolved in the soil water and eventually transported to the streamchannel with the flow of the groundwater. Today the quantities of dissolved organic carbon (DOC) have been observed to increase in many lakes and streams around the world, which constitute a threat against the water quality and ecologic environment of these surface waters. The amount of organic carbon that is dissolved and transported in the soil water is mainly controlled by processes related to temperature and hydrology, two factors which vary seasonally. Because of difficulties to sample soil water at temperatures below 0°C studies of DOC transport between soil and water during the winter season are limited. This study therefore conducted a winter sampling of soil water, with the focus on DOC. Samples were collected in March 2014 at sites along three hillslopes, orthogonal to two streams, in a typical Swedish boreal forest northwest of Umeå. The soil water was extracted with the help of suction lysimeters installed at different depths in the soil, and heating equipmentpowered by batteries. The collected samples were analyzed for DOC concentration and absorbance after which the results were grouped together with results from previous sampling campaigns, conducted in the summer and autumn of 2013. Parallel to this, data representing a longer time series (2009 to 2012) at another hillslope was processed. During the summer and autumn an increase in DOC concentration was observed. The increase was assumed to be caused by high production and effective degradation of organic matter in the soil during this warm period. Generally, a decrease in the DOC concentration then followed during the winter season. One possible reason for this decrease could be that the bacterial degradation in the soil continued, during the winter, and transformed the dissolved carbon into CO2 and CH4. Another possibility is that the DOC was flushed into the streams by autumn rain events. The study also found differences concerning the DOC concentration and character in the soil water, as well as the seasonal variation of these parameters, with soil depth and distance from the stream along the hillslope profile. These differences could be correlated to the organic content of the soil, from which the soil water had been extracted.

Air-water interface plays an important role in the transport of many contaminants in the vadose zone. It is also a limiting factor for many processes involve mass or energy transfer between air and water phases in vadose zone. In this research, the gas-phase partitioning tracer method was used to measure air-water interfacial area for eight porous media. The experimental results were used to investigate the influencing factors of the magnitude of air-water interfacial area and the relationship between the air-water interfacial area and water saturation, and capillary pressure. The porous media comprised a series of sands with narrow particle-size ranges, a sand with a wider particle-size distribution, a sandy soil, and a loamy sandy soil. The measurement range was extended to very low water contents in an attempt to determine upper limits for air-water interfacial areas. The measured values were compared to the normalized surface areas of the porous media. The results of the experiments showed that the magnitude of the air-water interfacial areas increased with decreasing water saturation, and approached that of the normalized surface areas. Generally, air-water interfacial areas were larger for media with larger specific surface areas. The change in air-water interfacial area with changing water saturation was less near saturated water contents and greater at smaller values. In addition, the change was greater for the poorly-sorted media than the well-sorted media. An empirical model was developed to describe the observed relationship between air-water interfacial area and water saturation. The coefficients of the model were found to correlate to the porous-medium uniformity coefficient. With this model and associated correlations, only bulk density, specific surface area, and uniformity coefficient are needed to estimate air-water interfacial area for a given water saturation. The model was shown to provide a reasonable description of a literature data set. Potential relationships between air-water interfacial area and capillary pressure under higher water-content conditions are investigated for unsaturated sandy porous media. A conceptual relationship between air-water interfacial area and capillary pressure is hypothesized, and is tested using air-water interfacial area data obtained from gas-phase tracer tests and saturation-pressure data obtained from water-drainage experiments. The results show that the magnitude of the air-water interfacial area increases with increasing capillary pressure, which corresponds to decreasing water content. (Abstract shortened by UMI.)

Modern urban stormwater infrastructure includes vegetated bioretention facilities (BRFs) that are designed to detain water and pollutants. Phosphorus (P) is a pollutant in stormwater which can be retained in BRF soils in mineral, plant, and microbial pools. We explored soil properties and phosphorus forms in the soils of 16 operational BRFs in Portland, OR. Since soil hydrology can significantly impact P retention, we selected BRFs along an infiltration rate (IR) gradient. We conducted sequential fractionation and tests of P pools and measured P release in a subset of soils after drying and flooding samples for ten days. We hypothesized that mineral or organic soil P forms would be correlated with IR, and that vulnerability to P release would depend on the interaction of drying and flooding treatments with P forms and pools. IR did not significantly explain differences in P forms. Soil TP was elevated across all sites, compared with TP in agriculturally-impacted wetlands and was substantially composed of soil organic matter (OM)-associated P. Phosphorus sorbed to mineral Fe and Al oxides- was variable but positively correlated with water-extractable P. The concentration gradient of water-extractable P was primarily controlled by overall P pools. Experimentally induced P releases were seen in 5 of 6 soils exposed to drying conditions, presumably released through microbial mineralization of OM. Only one site showed significant P release following the flooding treatment. Our measurements supported the idea that Fe and Al oxides provide P sorption capacity in these BRF soils. Variable inputs of P to BRFs through stormwater and litterfall may contribute to variability in P profiles and P release vulnerability across sites. Design specifications and management decisions relating to bioretention soils (e.g. establishment of acceptable soil test P levels, focusing on P forms known to influence vulnerability of P release) may benefit from detailed biogeochemical investigations.

Water availability is influencing crop yields in the Padmalaya watershed in Central Maharashtra, India, which are currently below potentially attainable yields. A number of rainwater harvesting structures such as in-stream check dams have been put in place, with the aim of improving water availability for agricultural production. The SWAT model was manually calibrated for hydrology using measured streamflow data from January to July 2010. Simulations were carried out for the period from 1977-2007 under various biophysical management conditions, with climatic data collected from the Jalgaon meteorological station. Future scenarios encompassing rainwater harvesting, climate change, land use change, and water conservation practices were evaluated. The simulation outputs were used to assess the impacts of the different factors on hydrological processes and crop yields for a 30-year period. Results show that in-stream structures significantly increase groundwater recharge. In addition, increased precipitation associated with climate change is likely to contribute to increased agricultural yields and crop water productivity. While the specific results from the simulations are limited to the Padmalaya watershed, the lessons learnt in terms of applicability of rainwater harvesting strategies in the context of climate change can be extended to similar agro-ecoregions of India.
La productivité des cultures dans le bassin versant Padmalaya en Inde est en-deçà de son plein potentiel, dû à une pauvre disponibilité des ressources en eau. Des structures de collection de l'eau pluviale ont été mises en place, ayant comme objectif d'augmenter la disponibilité de l'eau pour la production agricole. Le modèle hydrologique SWAT a été calibré manuellement pour l'aspect hydrologique, en utilisant des données de débit d'eau dans le basin versant de janvier à juillet 2010. Les simulations ont été faites pour la période 1977-2007, dans différentes conditions de gestion des terres, à l'aide de données météorologiques de la ville de Jalgaon. 16 scénarios ont été construits pour évaluer les impacts sur les processus hydrologiques et les rendements agricoles des changements climatiques, des systèmes de collection de l'eau pluviale, des changements d'affectation des terres, ainsi que des améliorations de pratiques de gestion de l'eau, sur une période de 30 ans. Les résultats des simulations démontrent que les structures de collection de l'eau pluviales contribuent de façon significative à la recharge des aquifères. De plus, l'augmentation des précipitations attribuable aux changements climatiques est susceptible d'engendrer une augmentation des rendements agricoles et de la productivité de l'eau pour les cultures. Malgré le fait que les résultats de ces simulations sont limités à ce bassin versant, les leçons apprises ici en termes d'applicabilité des stratégies de collection de l'eau pluviale dans le cadre des changements climatiques pourront être appliquées à de semblables agro-écorégions de l'Inde.

Quantifying groundwater recharge is of crucial importance for sustainable groundwater management. While many recharge quantification techniques have been devised, few provide spatially and temporally distributed estimates for regional-scale water resource assessments. In this study, a GIS-based and USGS-developed recharge quantification tool ? the Soil Water Balance (SWB) model ? was applied to produce fine-tuned recharge constraints and document spatial and temporal dynamics of recharge. SWB has, as of yet, been tested solely in coastal and continental temperate-humid climate zones. This study expands testing of SWB to a Mediterranean climate zone, focusing on Catalina Island, California. Catalina has experienced significant water supply issues due to a prolonged drought. Using available climate, land use/land cover and hydrology data, the SWB model yields annual recharge values for the time period 2008-2014 of 0.05 mm/year to over 82 mm/year. Results of this thesis provide information on spatial and temporal patterns of groundwater recharge on Catalina Island.

Pressurized hot water and DTPA-Sorbitol are two relatively new soil boron (B) extraction methods with potential to replace the cumbersome hot water extraction. The objective of this research is to produce data in support of acceptance or rejection of these two alternative B extractions. The three soil tests were used to extract B from samples of calcareous sand and silt loam and limed, loamy fine sand treated with 10 levels of B and incubated for 7 and 28 d. As B application increased so did extractable B with each extraction method. High correlations (r of 0.977 to 0.999) were observed between extractable B and rate of B application with all three methods. Hot water generally extracted the least and pressurized hot water the most B regardless of soil type, rate of application or duration of incubation. Greenhouse and field experiments were conducted on one limed acid and two alkaline soils naturally low in B to test alfalfa response to B fertilizer. Values from the three soil extraction methods were correlated to yield, B tissue concentration and total B removal of alfalfa. In greenhouse studies with varying levels of soil applied B, highly significant relationships exist between extractable soil B and both tissue B concentration and total B removal. Correlations between yield and extractable soil B were impossible to obtain because of a lack of alfalfa yield responses to applied boron. All three methods accurately predict plant B tissue concentrations and total B removal. The field experiment produced a significant positive relationship between total alfalfa yield and extractable B using hot water and pressurized hot water extractions, but not using DTPA-Sorbitol. The results observed in this research support pressurized hot water extraction as the better of the two alternatives to replace hot water extraction in a broad range of soil types.

ABSTRACT EFFECTS OF RECYCLED WATER ON LANDSCAPE PLANTS Casey Ray Miranda Recycled water is water that has been previously used, has suffered a loss of quality, and has been properly treated for redistribution (Wu et al. 2001). The use of recycled water as an alternative to fresh water in the landscape can have positive and negative effects. Experimentation on 40 different plant species during a 32 week period (2 phases of 16 weeks), was conducted to analyze the effects of recycled water irrigation on the appearance of landscape plants. Each species of plant was planted into 10 individual number 2 pots and irrigated with recycled water daily. Media and water were tested for nutrients and other constituents. In phase I there were four different species of grasses and grass-like plants, five different perennials, five species of shrubs, and four annuals tested; while phase II tested four species of herbaceous perennials, eight different species of shrubs, six species of groundcovers, and four species of annuals. All tests were conducted at the Paso Robles Waste Water Treatment Plant. Of the grasses and grass like species Yucca spp. and Buchloe spp. performed best. Osteospermum fruticosum, Lavandula angustifolia, Rosmarinus officinalis, Phormium tenax, and Pennisetum setaceum had the best appearance of the herbaceous perennials tested. For the shrubs, Coprosma repens, Cistus purpureus, Dodonea viscosa, Eleagnus pungens, Baccharis pilularis, Ceanothus thysiflorus, Thuja orientalis, and Nerium oleander had the best appearance when irrigated with recycled water. The best annuals were Senecio cineraria, Antirrhinum majus, Primula spp., Viola spp., and Calendula officinalis. Of the groundcovers Heuchera spp., Lonicera japonica, Vinca major, Hedera helix, and Ceanothus griseus had the best results. From the experiment a list of tolerant and non-tolerant plants was compiled (Appendices 1 and 2). While many plants were capable of developing and growing normally, other plants were sensitive to recycled water irrigation. In order to prevent salt damage to plants and expand the use of recycled water, salt tolerance of landscape plant material must be identified (Niu et.al, 2006).

Soil building processes were studied in reconstructed tree islands in the Loxahatchee Impoundment Landscape Assessment, Florida. Soil building was evaluated by measuring litter production, litter decomposition, soil accretion, and changes in soil elevation under different hydrologic conditions, and by determining physicochemical characteristics of newly accreted soils. Tree islands showed higher litter production and soil accretion but a larger loss of soil elevation caused by subsidence at higher elevations and shorter inundation periods. Newly accreted soils exhibited higher nutrient concentrations, and organic matter (OM) than older soils. Most of the soil phosphorus was stored in the organic fraction. A positive correlation was found between soil nutrients and OM. Reconstructed tree islands are increasing in soil OM and nutrients, generating a positive feedback that increases tree productivity, and soil building. These findings contribute to the understanding of tree islands’ dynamics and can be used by managers for restoration efforts in the Everglades.

The occurrence and disinfectant effectiveness for pathogens which are known or thought to be important in waterborne disease was evaluated. In the first study, the occurrence of human pathogenic microsporidia, Giardia cysts and Cryptosporidium oocysts in surface waters used for the irrigation of vegetable crops was determined. Twenty-eight percent of the irrigation water samples tested positive for microsporidia, 60% positive for Giardia cysts and 36% positive for Cryptosporidium oocysts. Concentrations of Giardia cysts and Cryptosporidium oocysts detected in water samples collected in Central America compared to the United States were 559 cysts and 227 oocysts, and 25 cysts and < 19 oocysts per 100 L, respectively. The presence of human pathogenic parasites in irrigation waters used for production of crops traditionally consumed raw suggests that there may be a risk of infection to consumers who come in contact with or consume these products. In the other investigations, the effectiveness of UV light and free chlorine on the inactivation of feline calicivirus (FCV) and enteric adenovirus type 40 (AD40) was assessed and compared to model viruses, poliovirus type 1 (PV-1) and coliphage MS-2. FCV was used as a model for members of the "Norwalk like virus" (NLV) group. The UV doses required to achieve 99% inactivation of AD40, coliphage MS-2 and FCV in buffered demand free (BDF) water were 108.6, 58.5 and 16.8 mWs/cm², respectively. For chlorine reactions, higher Ct values for high pH and low temperature conditions was observed for FCV and AD40. Both viruses were more resistant to chlorine than the well-studied PV-1. FCV and AD40 were inactivated rapidly by ∼0.5 mg/L free chlorine by ≥4.00- and ≥2.54-logs at pH 6 and 5°C whereas, PV-1 was not inactivated by 4.04-logs until 10 min contact time. Experiments conducted with aggregated FCV and PV-1 and experiments conducted in treated groundwater had slower inactivation kinetics than dispersed viral suspensions in BDF water. The high disinfectant decay rate of some experiments was most likely due to the decrease in chlorine concentration throughout the experiment. However, low disinfectant decay rates of the AD40 experiments suggest that aggregation or clumping of the viruses may have occurred. The results of these studies provide information on the effectiveness of two common water treatment disinfectants in waters with different physical and chemical qualities. The results of this study may provide a basis for the establishment of guidelines for proficient application in drinking water treatment.

Thesis (Ph. D.)--University of Kentucky, 2010.
Title from document title page (viewed on May 12, 2010). Document formatted into pages; contains: xii, 310 p. : ill. (some col.). Includes abstract and vita. Includes bibliographical references (p. 298-309).

The need for efficient use of water resources has increased the importance of optimum soil water usage in agricultural systems. Soil temperature has been shown to be important in influencing the early development of many plant species. Many agricultural regions have suboptimal soil temperature regimes for plant growth, and some cultural practices have been shown to reduce near-surface soil temperatures. The seasonal influence of soil temperature on soil water extraction and aboveground and belowground plant growth under variable irrigation was investigated at the USU Greenville Farm in Logan, UT. Soil surface mulches and buried heat cables were used to modify soil temperature. A line-source sprinkler system provided a gradient of water application. During 1987 yields were mainly influenced by irrigation. During 1988 greater soil temperature differences resulted in significant plant growth and yield responses. Soil water depletion corresponded to soil temperature treatments during the early part of the growing seasons. Depth of maximum soil water depletion was about 20 cm deeper for warm treatments. Water uptake rates of earlier-maturing plants in warm treatments were reduced later in the season, so that cumulative seasonal soil water depletion was similar for all temperature treatments. Although depth of rooting was somewhat greater under high than low irrigation during 1988, low irrigation treatments depleted soil water to greater depth. There was no interactive response of plant growth and yield or of soil water depletion to soil temperature and irrigation treatments. Modifications were made to a computer simulation model of the soil-plant-atmosphere system in order to more mechanistically simulate plant water uptake and to include influences of soil temperature on seasonal rooting growth and soil water extraction. The model adequately simulated both the pattern and magnitude of soil temperature influences on soil water depletion, and conclusions drawn from model simulations agreed with field observations during 1987 and 1988.

Currently, there is very little research available on nonpoint source pollution from rural watersheds. Government regulatory agencies are desperate for information regarding the causes of nonpoint source pollution, which includes the relationship between suspended soil particles and dispersion. Since soil dispersion is dependent on clay mineralogy, knowing the clay mineralogy of the soil in an area can help predict sediment loads entering the surrounding surface waters. This information is necessary to protect the resource value of our rivers, lakes, and estuaries, as well as to protect recreational activities such as fishing or hunting; but most importantly, this information is necessary to ensure the safety of our drinking water supply. Clay mineralogy and its influence on dispersion, as well as dispersion and its relation to water quality are the focus of this study. Soil mineralogy affects water quality in several ways: soil mineralogy determines the dispersivity of the clay portion of the soil and dispersive clays are likely to end up as suspended sediment in surface waters; weathering reactions contribute elements to water as dissolved load, and the sorption properties of clay minerals contribute to soils' ability to filter and carry pollutants. Through the use of X-ray diffraction, dispersivity, atomic absorption spectrometry, cation exchange capacity, and petrographic microscopy, this study shows that the clay mineral fraction of a soil determines the dispersivity, and that dispersed clay minerals contribute excess nutrients and metals as nonpoint source pollutants to surface waters.

This thesis investigates the abiotic control of carbon (C) and water vapour fluxes (FCO₂ and E, respectively) in a New Zealand Pinus radiata D. Don plantation and a nearby clearcut. It concentrates on the limitation of these fluxes imposed by growing season soil water deficit. This results from low precipitation (658 mm a⁻¹) in combination with a limited root zone water storage capacity of the very stony soil (> 30% by volume). The thesis analyses results from seven eddy covariance flux measurement campaigns between November 1994 and March 1996. The study site was located in Balmoral Forest, 100 km north-west of Christchurch (42° 52' S, 172° 45' E), in a (in November 1994) 8-year-old stand. One set of measurements was conducted in an adjacent clearcut. Ecosystem flux measurements were accompanied by separate measurements of ground fluxes and of the associated environmental variables. Flux analysis focussed on the underlying processes of assimilation (Ac), canopy stomatal conductance (Gc) and respiration (Reco), using biophysical models coupled to soil water balance and temperature subroutines. Aiming to link time inegrated net ecosystem C (NEP) to tree growth, sequestration in tree biomass (NPP) was quantified by regular measurements of stem diameter using allometric relationships. Average rates of FCO₂ and E were highest in spring (324 mmol m⁻² d⁻¹ and 207 mol m⁻² d⁻¹, respectively) when the abiotic environment was most favourable for Gc and Ac. During summer, fluxes were impeded by the depletion of available soil water (θ) and the co-occurrence of high air saturation deficit (D) and temperature (T) and were equal or smaller than during winter (FCO₂ = 46 mmol m⁻² d⁻¹ in summer and 115 mmol m⁻² d⁻¹ in winter; E = 57 and 47 mol m⁻² d⁻¹, respectively). With increasingly dry soil, fluxes and their associated ratios became predominantly regulated by D rather than quantum irradiance, and on particularly hot days the ecosystem was a net C source. Interannually, forest C and water fluxes increased strongly with rainfall, and the simultaneously reduced D and T. For two succeeding years, the second having 3 % more rain, modelled NEP was 515 and 716 g C m⁻² a⁻¹, Ac 1690 and 1841 g C m⁻² a⁻¹ and Reco 1175 and 1125 g C m⁻² a⁻¹. NEP / E increased in wetter (and cooler) years (1.3 and 1.5 g kg⁻¹), reflecting a relatively larger gain in NEP. Responding mainly to increased rainfall during commonly dry parts of the year (ie summer), and reflecting the otherwise benign maritime climate of New Zealand, NEP during the winter months could exceed NEP during the middle of the notional tree growing season. Annual Ac, NEP, and NPP were strongly linearly related. This relation did not hold during bi-weekly periods when the processes of intermediate C storage were influential. Separate knowledge of tree growth and C fluxes allowed quantification of autotrophic, and heterotrophic respiration (Rhet≈ 0.4 NEP), as well as fine-root turnover (≈0.2 NEP). The ratio of NEP and stem volume growth was conservative (0.24 t C m⁻³) and allows a direct connection to be made between ecosystem carbon fluxes and forest yield tables. In the absence of living roots, the clearcut flux measurements demonstrated the expected limitation of Rhet by soil temperature (Ts) and θ. However, an additional 'pumping effect' was discovered at the open site whereby turbulence increased CO₂ efflux considerably when the soil surface was wet. Accounting for the combined effects of Ts, θ and turbulence, annual Rhet at the clear-cut site (loss to the atmosphere) was »50 % of NEP (C sequestered from the atmosphere) in the nearby forest. Clearly, there is an important contribution of C fluxes during early stages of ecosystem development to the total C sequestered over the lifetime of a plantation.

Species diversity achieved by adding novel functional groups (warm-season grasses and non-leguminous forbs) to pasture land, along with traditional grasses and legumes, could aid in the capture of nutrients and water in pasture systems by offering complementary rooting architecture to aid in water and nitrogen uptake and decrease nitrogen leaching. Because these species may differ from commonly used grasses and legumes in their seasonal pattern of productivity, they could also extend or enhance growing-season productivity. The goal of this project is to better understand the role of plant diversity in 1) nitrogen use and 2) distribution of rooting dynamics and forage production. On a larger scale, this project hopes to identify pasture mixtures with greater diversity and management practices that maintain desirable pasture composition and livestock productivity. Herbage dry mass (DM), root surface area (RSA), and 15N uptake of nine species grown individually in the greenhouse were measured in the first experiment. Species which performed well or which were of particular interest to our study were used in mixtures in the second experiment, which contained varying numbers of functional groups. Individual species grown in monoculture varied in DM production over the course of the experiment, but there were no differences among mixtures, which all increased similarly in DM. Herbage DM of mixtures was 72 to 110% of that predicted by Experiment 1. The RSA of tap-rooted species was low and varied little with depth, while the RSA of cool-season grasses was higher closer to the soil surface. The RSA of mixtures decreased linearly with increased depth, and was between 150 and 350% higher than predicted from the RSA of individual species. Legumes, which have higher foliar protein content than grasses, accumulated more 15N in shoot DM than grasses, but mixtures did not differ from one another. It is concluded that the DM production advantage of mixtures is more consistent yield. Furthermore, increasing the diversity of simple grass-legume mixtures by adding non-leguminous forbs or other functional groups will likely improve water-use efficiency, thus reducing the risk of nitrate leaching compared with low-diversity grass-legume mixtures while fully exploiting biological nitrogen fixation.

Better management of water resources is a growing concern with increasing stress on natural resources. Despite technological improvements in the past decades, a method to instantaneously measure soil water flux remains elusive, especially at a resolution adequate for monitoring natural processes (i.e. 1 mm d-1). The objectives of this research were to evaluate and improve two emerging methods for water flux estimates, 1) streaming potential and 2) heat pulse measurements, as tools to perform at these low flux rates. Streaming potential measures a voltage between two electrodes resulting from water with charged particles generating a current as it flows between the charged surfaces of the soil. Heat pulse measurements, performed with a penta-needle heat pulse probe (PHPP), measure the transport rate and direction of a heat pulse as it propagates from a central needle to surrounding thermistors through soil. Water moving past this sensor carries heat and this allows estimation of water flux from measured heat flux. Streaming potential experimentation demonstrated a clear voltage response to low flow rates. Unfortunately, inconsistent results coupled with measurement complications – susceptibility to electromagnetic noise, drifting, etc. – led to difficulties when trying to establish a congruent relationship between flow rate and voltage behavior. We concluded that the necessary steps to potentially improve measurement consistency made streaming potential less desirable to pursue compared to other emerging tools for water flux measurements. Heat pulse work focused on modifying design parameters to improve low flux rate determination. We tested the effect of increasing heater needle diameter (from 2 mm to 5 mm), increasing heating time (from 8 to 24 and 40 seconds), and doubling heat input (from 120 W m-1 to 240 W m-1) in saturated sand. Results indicated that using larger heater needles and higher heat input improve flux estimation but increasing heating time resulted in marginal improvement. By using a PHPP with a 5 mm heater needle, 24 second heating time, and 240 W m-1 heating input, fluxes were resolved down to 1 cm d-1. Refinement of calibration procedures and inconsistencies between probes used must be resolved if measurement resolution is to be improved further.

This project implements a real application on the Spider II, which is a simulation of Soil Water Movement Model. The main objectives of this project were to develop a parallel and distributed algorithm for the Soil Water Model; implement the Soil Water Movement Simulation model on the Spider II distributed system and to evaluate the performance of simulating the Soil Water Movement Model on Spider II.

Soil erosion was assessed at Camp Williams National Guard Base by creating an erosion risk classification map and comparing the erosion impact of disturbance regimes on different hillslopes. Soil erosion does not appear to be a problem for most of Camp Williams. The Revised Universal Soil Loss Equation was applied using GIS to create a soil erosion risk map for the entire Camp Williams facility. The map indicated where problem areas occurred and showed relative erosion risk, but its lack of quantitative accuracy should be noted. Areas of concern included landscapes with little or no protective vegetation such as roads, abandoned agricultural fields, and sensitive riparian areas where gullies tend to form and expand. The Water Erosion Prediction Project model was used to evaluate the erosion impacts of various disturbances on five study hillslopes. The model did not appear to function well on the Camp Williams study hillslopes because the distribution of infiltration rates could not be satisfactorily represented. However, hydraulic conductivity measurements collected for this task were useful in providing insight into some of the physical processes of erosion. The hydraulic conductivity measurements showed some of the impacts of military activities, grazing, and wildfire on soil properties. Erosion bridges were also used on the five study hillslopes in an attempt to measure soil Joss and deposition. However, the bridges Jacked the capability of measuring the low rates of erosion during the time period set for this experiment. The bridges showed potential for measuring erosion in rills, gullies, highly disturbed areas, or in longer duration experiments.

Root Zone Soil Moisture (RZSM) data have both drought monitoring and seasonal forecasting applications. It is the lifeblood of vegetation, an integral component of the hydrologic system, a determining factor in irrigation requirements, and works to govern the means by which energy imbalances are settled between land and atmosphere. The National Integrated Drought Information System (NIDIS) has worked in conjunction with the Colorado Climate Center to improve regional drought early warning through enhanced monitoring and understanding of RZSM. The chief goals of this research have been as follows: 1. Examine regional drought monitoring in the Upper Colorado River Basin and eastern Colorado with specific inquiry as to soil moisture’s role in the process. 2. Develop operational products that can be used to improve the weekly drought monitoring process in the Upper Colorado River Basin and eastern Colorado with an emphasis on utilization of soil moisture data. 3. Review in-situ soil moisture data from high elevation Snow Telemetry measurement sites in Colorado in order to understand the descriptive climatology of soil moisture over the Colorado Rockies. 4. Compare output from soil sensors installed by the Snow Telemetry and Colorado Agricultural Meteorological Network using current calibration methods in order to better understand application of direct comparison between output from the two different sensor types. Engineer a soil moisture core measurement protocol that is reliable within ten percent of the true volumetric water content value. This protocol, if successful on a local plot, will be expanded to alpha testers around the United States and used by the USDA for drought monitoring as well as NASA for ground validation of the Soil Moisture Active Passive (SMAP) Satellite. 5. Expose the seasonality and spatial variability of positive feedbacks that occur between RZSM and the atmosphere across the Upper Colorado River Basin and western High Plains using reanalysis data from the North American Land Data Assimilation System Phase-2 (NLDAS).

Regional drought monitoring was found to involve assimilation of data from a bevy of sources. The decision-making process includes assessment of precipitation, soil moisture, snowpack, vegetative health, streamflow, reservoir levels, reference evapotranspiration, surface air temperature, and ground reports from the regional agricultural sector. Drought monitoring was expanded upon in this research through the development of several products intended for future Colorado Climate Center use. In-situ soil moisture timeseries are now being created from select SNOTEL and SCAN measurement sites. Reservoir monitoring graphics are being produced to accompany spatial analyses downloaded from the bureau of reclamation. More soil moisture data is being used, and now come from an ensemble of models rather than just the VIC model.

While only ten years of data were collected in analyzing the descriptive soil moisture climatology of the Colorado Rockies, these data were telling in terms of the expected seasonal cycle of soil moisture at high elevations. SNOTEL measurements reveal that soil moisture levels peak prior to snowmelt, large decreases in soil moisture are expected in June and early July, a slight recovery is anticipated in association with the North American Monsoon, and the sign of near-surface water balance flips back to positive in the first two weeks of September before soils freeze. Seasonal variance and distribution of volumetric water content varies in ways that are useful to understand from a drought monitoring standpoint. The data show that measurements are affected when soil freezes.

Comparing output from soil sensor relays using sensor types and calibration methods consistent with current SNOTEL and CoAgMet specifications revealed large differences in output regardless of being subject to the same meteorologic conditions.

Soil moisture measurement protocol development proved to be a trial and error process. The data collected at Christman Field was not sufficient proof that soil coring results did come within ten percent of ground truth perhaps due to microscale variations in infiltration. It was possible to develop a protocol of an acceptable standard that could be followed by citizen scientist for an estimated cost of $50.

Results from statistical modeling of post-processed NLDAS data from the last 30 years point primarily to a time frame between May and July in which soil moisture anomalies become significantly correlated with seasonal temperature and precipitation anomalies. This time of year is partially characterized by a climatologic maximization of downwelling solar radiation and a northward recession of the polar jet, but also precedes the anticipated arrival of the North American Monsoon. (Abstract shortened by ProQuest.)

Transport of chemical substances through a catchment depend to a large extent on the water content of the soil through which they are transported. When the groundwater level rise and fall, redox conditions change in the soil and the transport of substances is affected.

The aim of this study is to develop a hydrological model which is able to simulate soil water content at different depths and groundwater level in a soil profile. A new type of conceptual model is developed, which uses a continous represenation of the soil and soil water from the soil surface down to the bedrock. The model is intended to be applied on small catchments at a later stage.

The results show that the simulation of groundwater levels was greatly improved compared to previous results. Simulation of soil water content at selected depths is not yet satisfactory. The runoff simulation was accurate at one of the sites but did not work as well at the other. At one of the sites it was also possible to combine good simulations of runoff and groundwater levels but at the other it was only possible to obtain acceptable simulations of either runoff or groundwater.

It is suggested that model performance could be improved by letting the porosity decrease and the soil water content increase non-linearly with depth. Calculations of evaporation from soil and runoff also need to be modified.

The Nogales International Wastewater Treatment Plant releases treated wastewater from both Nogales, Arizona and Nogales, Sonora, Mexico into the Santa Cruz River. In recent years, the discharged effluent has contained high levels of cadmium and nickel, which exceed the plant's permit standards. Due to the industrial demographic of the region, outdated infrastructure, and differences in sampling schedules of multiple organizations, the treatment facility and the treated effluent is an important area of study. To understand how the treated effluent is affecting the river, data were compiled from existing water quality databases and flow reports from 2008 to 2015. To address how flow quantity has changed during drought periods, effluent flows were compared to historical flood data produced by the USGS. To evaluate water quality issues, water quality reports produced by the International Boundary and Water Commission were examined for past exceedances of constituents. According to flow volumes reported at the U.S.-Mexico border, the majority of the effluent was produced in Nogales, Sonora. Results showed that spikes in effluent flow corresponded with rainfall events. Results also show that rainfall influences the flow volumes from Nogales, Arizona, but there is little impact to flow volumes from Mexico. Although the quality of the effluent generally meets the permitted standards, exceedances did occur. The potential impact of such exceedances on stream water quality was evaluated using measured and simulated data. Although outreach to stakeholders across the border and updated infrastructure has improved the quality of water in the river, there are still many areas to improve upon, including sampling and monitoring schedules. To identify opportunities for improvement, further studies should examine the specific fate of each contaminant present in the effluent.

An intrinsic link exists between soil moisture and soil nitrogen. Factors that increase or decrease soil moisture can have a profound effect on soil nitrogen cycling, which may have later repercussions in the plant community. Post-fire soil water repellency is one factor that can limit soil moisture acquisition and may indirectly affect nitrogen cycling and weed invasion in woody islands of fertility. Plots centered on burned Juniperus osteosperma trees were either left untreated or treated with a surfactant to ameliorate water repellency. Two years later, soils were excavated from the untreated and treated field plots. In the greenhouse, half of each soil type received a surfactant treatment while the other half was left untreated. Pots were seeded with either Bromus tectorum or Pseudoroegneria spicata. Analysis of field soil prior to the greenhouse trial showed that untreated, repellent soils had inorganic nitrogen levels an order of magnitude higher than wettable, surfactant-treated soils. Greenhouse pots that had received a surfactant treatment in the field and/or greenhouse had similar soil water content, plant density, and above ground biomass, which were, respectively, 55-101%, 31 to 34 -fold, and 16 to 18 -fold greater than pots without a surfactant treatment. No species effects were found. This study indicates that water repellency can reduce wetting and retention of water in the soil while promoting the retention of high levels of inorganic nitrogen. However, the effects of soil water repellency on inorganic nitrogen appeared to have a minimal effect on plant growth compared to the effect of soil water repellency on water availability.

This study has provided fundamental information on the fate of urine nitrogen (N) when applied to pasture soils. In this work the three pasture soils used were a Bruntwood silt loam (BW), an old well-developed (lime and fertilizer incorporated and farmed for more than 20 years) peat soil (OP) and a young peat (YP) which was less developed (farmed for about 10 years). Initial soil chemical and physical measurements revealed that the peat soils were acidic, had higher cation exchange capacities, had greater carbon:nitrogen ratios and were better buffered against changes in soil pH than the BW soil. However, the BW soil was more fertile with a higher pH. The peat soils had lower bulk densities and higher porosities. Four experiments were performed. In the first experiment ¹⁵N-labelled urine was applied at 500 kg N ha⁻¹ to intact soil cores of the three soils. Treatments imposed were the presence and absence of a water table at two temperatures, 8°C or 23° C, over 11-14 weeks. ¹⁵N budgets were determined. This first experiment showed that the nitrification rate was faster in the BW soil and was retarded with a water table present. Significant leaching of nitrate occurred at 8°C in the BW soil without a water table. This was reduced when a water table was present. Leaching losses of urine-N were lower in the peat soils than in the BW soil. Apparent denitrification losses (i.e. calculated on a total-N recovery basis) ranged from 18 to 48 % of the ¹⁵N-applied with the greatest losses occurring in the peat soils. The second experiment examined denitrification losses, over 30 days, following the application of synthetic urine-N at 420 kg N ha⁻¹ to small soil cores situated in growth cabinets. The effects of temperature (8°C or 18°C) and synthetic urine (presence or absence) were measured on the BW and OP soils. Nitrous oxide (N₂0) measurements were taken from all soil cores and a sub-set of soil cores, at 18°C, had ¹⁵N-labelled synthetic urine-N applied so that ¹⁵N-labelled nitrogen gases could be monitored. This experiment showed that the application of synthetic urine and increased soil temperature enhanced denitrification losses from both soils. Denitrification losses, at 18°C, as ¹⁵N-labelled nitrogen gases accounted for 24 to 39 % of the nitrogen applied. Nitrous oxide comprised less than half of this denitrification loss. Losses of N₂0 in leachate samples from the soil cores accounted for less than 0.1 % of the nitrogen applied. A third experiment, using Iysimeters, was performed over a 150 day period in the field. The six treatments consisted of the 3 soils with applied synthetic urine, with or without a simulated water table; each replicated three times. Lysimeters were installed in the field at ground level and ¹⁵N-labelled synthetic urine-N was applied (500 kg N ha⁻¹) on June 4 1992 (day 1). Nitrification rates differed between the soils following the trend noticed in the first experiment. As in the first experiment, nitrate was only detected in the leachate from the BW soil and the inclusion of a water table reduced the concentration of nitrate. In the BW soil, the leachate nitrate concentrations exceeded the World Health Organisation's recommended limit (< 10 mg N L-1) regardless of water table treatment. No nitrate was detected in the leachates from the peat soils but there was some leaching of organic-N (< 5 % of N added) in all the peat soil treatments. Denitrification losses were monitored for the first 100 days of the experiment. In the BW soil without a water table, N₂0 production peaked at approximately day 20 and accounted for 3 % of the nitrogen applied. In the peat soils the measured denitrification losses accounted for less than 1 % of the nitrogen applied. Apparent denitrification losses in the peats were, however, calculated to be approximately 50 % of the ¹⁵N-labelled synthetic urine-N applied. It is postulated that the difference between apparent denitrification losses and those measured could have been due to; loss of dinitrogen in leachate, protracted production of dinitrogen below detectable limits, production of denitrification gases after measurements ceased (i.e. days 100 to 150) and entrapment of dinitrogen in soil cores. Due to the apparent denitrification losses being so high, further research into this nitrogen loss pathway was performed. The fourth and final experiment measured denitrification directly using highly enriched (50 atom %) ¹⁵N-labelled synthetic urine-N. It was performed in a growth cabinet held initially at 8°C. The ¹⁵N-labelled synthetic urine was applied at 500 kg N ha⁻¹ to small soil cores of each soil type. Fluxes of N₂0 and ¹⁵N-labelled gases were measured daily for 59 days. On day 42 the temperature of the growth cabinet was increased to 12°C in an attempt to simulate the mean soil temperature at the end of the field experiment. Up to this time, production of nitrogenous gases from the YP soil had been very low. Interpretation of gaseous nitrogen loss in the YP soil was difficult due to the possibility of chemodenitrification occurring. However, in the OP and BW soils, gaseous losses of nitrogen (determined as ¹⁵N-labelled gas) represented 16 and 7 % of the nitrogen applied respectively. Nitrous oxide comprised approximately half of this gaseous nitrogen loss, in both the OP and BW soils. This work implies that urine-N applied to the mineral soil (BW) could potentially threaten the quality of ground water due to nitrate contamination through leaching. In contrast, denitrification appears to be the major loss mechanism from the peat soils, with the production of nitrous oxide being the primary focus for any environmental concern. Future work should examine the fate of the nitrate leached from the BW soil and the potential for dilution, plant uptake or denitrification below a 30 cm soil depth. A better understanding of the denitrification mechanisms could help reduce denitrification and thereby improve the efficiency of nitrogen use and reduce the output of nitrous oxide.

Irrigated agriculture is the primary consumer of limited worldwide freshwater resources. Drought, growing world populations, and environmental demands compete with irrigation for freshwater resources"”threatening sustainable global food, fuel, and fiber production. This escalating global crisis demands that agriculture produce more food using less water. Traditional irrigation management has used technology to apply uniform irrigation rates across landscapes"”ignoring natural environmental variation. This provides inherent inefficiencies of over- or under- irrigation within individual fields. Variable-rate irrigation (VRI) is modern technology that employs global positioning systems and geographic information systems to match irrigation to spatially variable crop water demands within a field. Although commercially available, VRI lacks scientifically validated decision support systems to determine spatially and temporally variable crop water demand. The purpose of this research is to explore spatial and temporal variations in crop water demand to inform growers utilizing VRI. This research consists of four seasons of winter wheat (Triticum aestivum L.) production on a commercial farm in Idaho that employs a VRI system. In Chapter 1, the spatial variation of crop water productivity (CWP, the grain produced per unit of water consumed), is characterized for two seasons (2016-2017) and we propose a unique conceptual strategy for VRI management targeted at CWP. Observed CWP ranged from 4.1-21 kg ha-1 mm-1 with distinct spatial variation that, when considered together with grain yield, were shown to be useful for VRI management. During the 2017 growing season, VRI zones conserved 25% of irrigation compared to traditional uniform irrigation management. In the second chapter the spatial variation of soil water holding capacity (SWHC) was measured at 90 sampling points throughout the field. Then, during the 2016-2017 growing seasons, the spatial and temporal variation of soil moisture were modelled to characterize crop stress and its influence on grain yield. Soil within the field showed large spatial variation of SWHC, ranging from 147-369 mm. Under uniform irrigation in 2016, the natural variation of TAW created 21 day variation in the onset of crop stress throughout the field and under VRI in 2017 the onset of crop stress spanned 56 d. Surprisingly the variations in TAW did not statistically influence yield in 2016, and in 2017 the rate of irrigation predicted yield and TAW again did not statistically predict yield. This suggests that other environmental variables should be included when delineating irrigation zones and rates for VRI.

Chlorine is an element commonly found in the environment of our planet, in the atmosphere, the earth crust and the oceans. Chlorine occurs in two forms, inorganic chloride (Cl_in) and organically bound chlorine (Cl_org), also called organochlorine. For a long time, the organic halogens (among them the organic chlorine) had been considered as produced only by human activities. However, the research of the recent decades suggests a considerably amount of naturally produced organic chlorine in soil and water. Through the research, a hypothesis have emerged, suggesting that there occur a formation of organic chlorine in the top soil layer where chloride is consuming, while the organic chlorine is degrading on deeper soil levels, causing a release of chloride. The study in this thesis attempts to explore the transportation of organic chlorine through soil. 49 soil water samples were collected at three transects, S04, S12 and S22, nearby a stream in northern Sweden and analysed for Cl_org, using an AOX-analyser. The results suggest a decrease in concentrations of Cl_org by soil depth for transects S04 and S12. The study also indicates that concentrations of Cl_org are decreasing with increasing distance from the stream, where the highest mean concentration was found in the organic matter-rich riparian transect S04. Further conclusions are that the spring flood and changes in groundwater level may influence the concentrations of Cl_org.

Ämnet klor är vanligt förekommande på vår planet och finns både i atmosfären, jordskorpan och världens oceaner. Klor uppträder i två olika former: oorganisk klorid (Cl_in) och organiskt bundet klor (Cl_org). De organiska halogenerna (bland vilka organiskt klor ingår) har under lång tid ansetts härstamma från enbart antropogena källor. De senaste decenniernas forskning har dock tytt på en naturlig produktion av organiskt klor i mark och vatten. Genom denna forskning har en hypotes tagit form som föreslår en bildning av organiskt klor i de övre marklagren, där klorid binds, medan det i djupare marklager sker en nedbrytning av det organiska kloret vilket medför ett frigörande av klorid. Denna studie syftar till att studera transporten av organiskt klor genom mark. 49 stycken markvattenprover insamlades vid tre provpunkter (S04, S12 och S22) på ett avrinningsområde i norra Sverige och analyserades med hjälp av ett AOX-instrument. Resultaten tyder på en minskning av Cl_org med ökande markdjup för provpunkterna S04 och S12. Studien visar även en minskning i koncentration av organiskt klor med ökande avstånd till vattendraget, där den högsta medelkoncentrationen återfanns i provpunkten S04 som ligger nära bäcken och är rik på organiskt material. Vidare slutsater är att vattenflödena under vårflod samt variasionen i grundvattennivå har en påverkan på koncentrationerna av Cl_org.

The quantification and prediction of soil properties is fundamental to further understanding the Critical Zone (CZ). In this study we aim to quantify and predict soil properties within a forested catchment, Marshall Gulch, AZ. Input layers of soil depth (modeled), slope, Saga wetness index, remotely sensed normalized difference vegetation index (NDVI) and national agriculture imagery program (NAIP) bands 3/2 were determined to account for 95% of landscape variance and used as model predictors. Target variables including soil depth (cm), carbon (kg/m²), clay (%), Na flux (kg/m ²), pH, and strain are predicted using multivariate linear step-wise regression models. Our results show strong correlations of soil properties with the drainage systems in the MG catchment. We observe deeper soils, higher clay content, higher carbon content, and more Na loss within the drainages of the catchment in contrast to the adjacent slopes and ridgelines.

It is proposed that microbial polysaccharides behave anion-exclusively, permitting the transport of cations, but excluding the diffusion of anions. This hypothesis has been investigated in the context of polysaccharides produced by microorganisms in the rhizosphere. The anion-exclusive behaviour of exopolysaccharides, extracted from broth cultures of a range of rhizosphere microorganisms together with several commercial polysaccharides (i.e., xanthan, scleroglucan, dextran, guar gum) was investigated by measuring the electrochemical potential which developed as a result of the diffusion of KC1 across a polymer layer. Considering xanthan as a 'model' microbial polysaccharide, polymer concentration, layer thickness and the presence of either O-acetyl or pyruvyl groups were found to positively affect the degree of anion exclusion. The anion-exclusive behaviour of xanthan was verified by direct ion analysis of solutions either side of the polymer layer. It was found that in a range of ionic environments, the diffusion of anions was reduced by ~70% by the presence of a 3% w/w xanthan layer. The influence of xanthan on the diffusion of cations was studied using magnetic resonance imaging. In contrast to the proposed theory of anion exclusion, the rate of cation (Mn2+) diffusion through a 3% w/w xanthan layer was found not to be greater than that through free aqueous solution. The possible occurrence of anion exclusion and consequences thereof in the rhizosphere were assessed by studying the effect of substitution of the water films in soil with a layer of 3% xanthan on the growth of wheat seedlings. The phosphate, but not potassium content of those plants grown in soil with xanthan was ~20% lower than in the control plants. Those plants grown in xanthan-amended soil produced ~30% more biomass by dry weight. The anion-exclusive properties of polysaccharides produced naturally in bulk soil, the rhizosphere and root surface of pea was studied by the measurement of diffusion potentials. All three were found to show a high level of anion exclusion. The influence of O-acetyl groups in xanthan on the rate of water transport and degree of water binding was studied using stray field NMR methods. It was found that removal of O-acetyl groups reduces the rate of water transport and increases the rate of water binding at any given xanthan concentration. It is proposed that microoganisms produce anion-exclusive polysaccharides in the rhizosphere to protect themselves against the potentially lethal effects of water stress.

The work presented in this thesis investigates the effects of precipitation chemistry on the chemical characteristics of upland organic soils in the UK and their associated drainage waters. It also describes effects on a number of microbially-mediated processes and concludes with a study on methods for the amelioration of peat acidification. Data presented in chapters 3, 5 and 6 have recently been published or accepted for publication (Sanger et al. 1993 a. 1993 b and 1993 c). The first chapter describes the nature of soil acidity and reviews the relevant literature on the effects of acidic deposition, with particular emphasis on upland organic soils and their drainage waters. Chapter 2 describes a field survey carried out in the UK which investigates relationships between the exchangeable and total element chemistry of peat and precipitation chemistry. The results showed that peat collected from areas receiving high concentrations of H+, NH4+, SO42- andNO3- in precipitation were characterised by high extractable NH4+ and total P. and low extractable NO3-, base saturation and exchangeable Ca2+ and Mg2+. TheNH4+ concentration in precipitation was strongly related to a number of soil chemical parameters and the results suggest that future changesin NH4+ inputsto peatscould significantlyeffect soil and drainage water chemistry. The results also show that (1) processes involved in the cycling of N and P may have been altered by precipitation chemistry (2) exchangeable Ca2+ and Mg2+ have been displaced by NH4+ and H+ in areas with high acidic deposition. Peat from areas with a high marine input in precipitation contained high concentrations of exchangeable N+ and K+. Laboratory simulation studies (chapter 3 and 4) using intact peat monoliths were carried out to complement the regional survey described in chapter 2. They were set up to examine element fluxes from peats in relation to precipitation chemistry.

Fruit growers in Utah and other areas across the Intermountain West are faced with growing production challenges stemming from declining soil quality and water resources. Population growth presents challenges in terms of the cost and availability of land, but also presents opportunities in the form of new marketing options such as organic fruit. Few certified organic fruit orchards are operating in Utah currently, which is attributed to a lack of locally tested and adapted organic management practices. An organic peach orchard trial evaluated the effectiveness of different organic management approaches to enhance soil quality and conserve water without compromise to fruit tree growth and fertility. Two tree-row treatments: ‘straw mulch' (Triticum aestivum L.) and ‘living mulch’ (Lobularia maritima (L.) Desv.) were tested in combination with two alleyway groundcovers: ‘grass’ (Festuca rubra L. with Lolium perenne L.) and a legume, ‘Birdsfoot trefoil’ (Lotus corniculatus L.). The novel systems were compared with industry standards, tillage and weed fabric tree-rows with grass alleyways. Trefoil alleyway biomass deposited into tree-rows contributed an estimated 6.24 kg biomass and 0.21 kg total N/tree annually. Trefoil treatments had higher levels of organic carbon (C) and nitrogen (N), inorganic N, microbial biomass and enzyme activities, suggesting trefoil alleyways enhanced soil nutrient cycling, as well as C and N reserves in comparison to grass and tillage treatments. A functional gene array analysis was conducted to describe the mechanisms, microbial functional composition and diversity underlying the observed soil processes, however few differences were detected in soil community structure between soils under different orchard floor management. Significantly lower leaf δ15N in trees grown with trefoil compared to grass, and an association between root biomass, diameter and trunk cross-sectional area (TCSA) suggests nitrogen sources derived from the trefoil groundcover contributed to improved fruit tree vigor. Few differences resulted among orchard treatments for water use (mm/week). Trends indicated slightly higher water use in trefoil over grass, but not enough to offset observed soil quality and tree growth benefits. These findings suggest, trefoil alleyways may provide ecological benefits such as improved soil quality and efficient nutrient cycling, without substantial increases in water use.

The potential of proximal soil sensing methods for high resolution investigation of soils in the landscape has been investigated. This addresses the need for improved environmental monitoring and management of soils within their environs. On-the-go electromagnetic (EM) mapping has been used to map soils, providing a high resolution (< 10m) spatially defined soil apparent electrical conductivity (ECa) datalayer. Vis-NIR field spectroscopy has been trialled for in situ analysis of soil carbon, nitrogen and moisture. The portable spectroradiometer has been used at 6 sites in the Taupo-Rotorua region for rapid, field analysis of soil carbon (R2 calibration = 0.95, R2 prediction = 0.75,) soil nitrogen (R2 calibration = 0.95, R2 prediction = 0.86) and moisture (R2 calibration = 0.96, R2 prediction = 0.70) by collecting reflectance spectra from the flat surface of a soil core; and at one Manawatu site for soil moisture (R2 calibration = 0.79, R2 prediction = 0.71), where the reflectance spectra were collected directly from a freshly cut in situ soil surface. EM mapping and Vis-NIR field spectroscopy were used in combination to spatially characterize soil moisture patterns at the Manawatu site. Soil available water-holding capacity (AWC) of ECa-defined zones has been assessed at six irrigated production farming sites. Two methods (predicted AWC v ECa; estimated AWC v ECa) have been used to relate soil ECa to soil AWC to predict spatial AWC (R2 = 0.8 at 5 sites). Site-specific soil water balance models have been developed at all sites; and a wireless real-time soil moisture monitoring network has been trialled at two sites, to be used with the ECa-AWC prediction model for the development of daily soil water status maps, for variable rate irrigation (VRI) scheduling. This digital, spatially defined soil water status information is available for upload to a sprinkler system modified for variable rate application. The calculated water savings with VRI were 926% with equivalent energy savings and improved irrigation water use efficiency. Drainage and runoff were reduced by 055% during the period of irrigation, with the accompanying reduced risk of nitrogen leaching. The reduction in virtual water content of product has also been assessed for VRI and compared with uniform rate irrigation (URI) at three study sites. This study suggests that these proximal sensing methods provide a new improved way of monitoring and mapping soils. This facilitates soil inventory mapping, for example soil moisture and carbon mapping. In addition, these high resolution environmental monitoring and mapping techniques provide the information required for optimizing site-specific management of natural resources at the farm scale. On-the-go electromagnetic (EM) mapping has enabled a step change in the pedological investigation of New Zealand soils. Resulting soil ECa maps provide a tool for improving traditional soil map boundaries because they delineate soil zones primarily on a basis of soil texture and moisture in non-saline soils. In this study the maps have been used for site-specific irrigation management at the farm-scale, aiming to increase the energy efficiency of this land management operation. The study has developed a method for improved use of freshwaters by more accurate irrigation scheduling, based on high resolution characterization of spatial and temporal soil differences.

The System of Rice Intensification (SRI) is a resource-conserving rice production system that uses intermittent flooding and organic fertilization. The SRI is emerging as an alternative to conventional rice production systems that use continuous flooding and mineral fertilizer only, however yield improvements with SRI have been highly variable. The objective of this research was to determine if soil properties control the yield improvements with SRI and, if so, the underlying chemical and biological mechanisms. A meta-analysis of 72 SRI vs. conventional system trials from 16 countries found a significant yield response to SRI in low fertility soils (P<0.0001), but no difference between SRI and the conventional system in moderate and high fertility soils. These results were validated in a greenhouse study. Soils with low P availability (≤7.1 mg P kg-1) responded positively to intermittent flooding and organic fertilizer by increasing plant biomass, plant P uptake, available soil P and microbial P concentrations, compared to soils under continuous flooding and amended with mineral NPK fertilizer only. A field study investigating the interactive effects of water regime and fertilizer source found that, under conditions of P limitation, yields were greater with NPK + composted cow manure (compost) than NPK fertilizer alone in the intermittently flooded (6.6 t ha-1 vs. 4.9 t ha-1) and continuously flooded (6.8 t ha-1 vs. 6.2 t ha-1) soils. The available soil P concentration was significantly increased by compost and was correlated with yield (P=0.007). When N was the most limiting nutrient, according to the Diagnostic and Recommendation Integrated System (DRIS) analysis, yields were greater in the continuously flooded (5.2 t ha-1) than intermittently flooded (2.7 t ha-1) soils receiving NPK fertilizer only, but showed no difference when compost was applied. Compost had a positive effect on the crop nutrient balance according to DRIS analysis (P=0.0007). On-farm trials of SRI at 10 locations in Panama showed an average yield increase of 47% and 86% less water use. SRI is recommended as a rice production system to conserve water and improve rice yields under conditions of P limitation. Organic fertilization is recommended to improve crop nutrient balance and yield under intermittently flooded soil conditions.
Le Système de Riziculture Intensive (SRI) est un système de production du riz qui préserve les ressources naturelles en utilisant l'irrigation intermittente et la fertilisation organique. SRI apparait comme une alternative aux systèmes de production de riz conventionnels qui utilisent l'irrigation continue et seulement des engrais minéraux; cependant les améliorations de rendement avec le SRI ont été très variables. L'objectif de cette recherche a été de déterminer si les améliorations de rendement dépendent des propriétés du sol avec SRI et quels sont les mécanismes chimiques et biologiques sous-jacents. Une méta-analyse de 72 tests SRI vs systèmes traditionnels dans 16 pays a révélé une réponse significative du rendement au SRI sur sols à faible fertilité (P<0.0001) mais pas de différence sur des sols à moyenne et forte fertilité. Ces résultats ont été validés par une étude en serre. Des sols bas en P (≤7.1 mg P kg-¹) ont réagis positivement à l'irrigation intermittente et aux engrais organiques en augmentant la biomasse de la plante, l'assimilation P, la disponibilité du P du sol, les concentrations microbiennes de P, comparativement aux sols avec irrigation continue et modifiés avec des engrais minéraux NPK seulement. Une étude de terrain investiguant les interactions des types d'alimentation en eau et des types d'engrais a démontré que dans les conditions de limitation de P, les rendements étaient plus importants avec NPK + fumier de vache (compost) qu'avec l'engrais NPK seul sur sols irrigués par intermittence (6.6 t ha-¹ vs 4.9 t ha-¹) et sur sols irrigués en continue (6.8 t ha-¹ vs 6.2 t ha-¹). La concentration P a été augmentée de façon significative par le compost et corrélée au rendement (P=0.007). Selon l'analyse du Système Intégré de Diagnostic et Recommandation (DRIS), lorsque l'N était la substance nutritive la plus limitée, les rendements étaient meilleurs sur des sols à irrigation continue (5.2 t ha-¹) que sur sols à irrigation intermittente (2.7 t ha-¹) en utilisant l'engrais NPK seulement, mais les rendements n'étaient pas différents quand le compost était utilisé. Le compost avait un effet positif sur l'équilibre des substances nutritives de la récolte selon l'analyse de DRIS (P=0.0007). Des essais du SRI dans les fermes à différents endroits du Panama ont montré une augmentation moyenne du rendement de 47% et ont utilisé 86% de moins d'eau. SRI est recommandé en tant que système de production du riz pour préserver l'eau et pour augmenter les rendements de production du riz dans les conditions de limitation du P. La fertilisation organique est recommandée pour améliorer l'équilibre des substances nutritives de la récolte et du rendement dans les conditions de sols irrigués par intermittence.

Stormwater runoff from existing impervious surfaces needs to be managed to protect downstream waterbodies from hydrologic and water quality impacts associated with development. As urban expansion continues at a rapid pace, increasing impervious cover, and climate change yields more frequent extreme precipitation events, increasing the need for improved stormwater management. Although green infrastructure such as bioretention has been implemented in urban areas for stormwater quality improvements and volume reductions, these systems are seldom monitored to validate their performance. Herein, we evaluate flow attenuation, stormwater quality performance, and nutrient cycling from eight roadside bioretention cells in their third and fourth years of implementation in Burlington, Vermont. Bioretention cells received varying treatments: (1) vegetation with high-diversity (7 species) and low-diversity plant mixes (2 species); (2) proprietary SorbtiveMediaTM (SM) containing iron and aluminum oxide granules to enhance sorption capacity for phosphorus; and (3) enhanced rainfall and runoff (RR) to certain cells (including one with SM treatment) at three levels (15%, 20%, 60% more than their control counterparts), mimicking anticipated precipitation increases from climate change. Bioretention water quality parameters monitored include total suspended solids (TSS), nitrate/nitrite-nitrogen (NOx), ortho-phosphorus (Ortho-P), total nitrogen (TN) and total phosphorus (TP), which were compared among bioretention cells’ inflows and outflows across 121 storms. Simultaneous measurements of flow rates and volumes allowed for evaluation of the cells’ hydraulic performances and estimation of pollutant load and event mean concentration (EMC) removal. We also monitored soil CO2 and N2O fluxes, as they represent a potential nutrient loss pathway from the bioretention cells. We determined C and N stocks in the soil media and vegetation, which are critical design elements of any bioretention, to determine the overall C and N balances in these systems. Significant average reductions in effluent stormwater volumes and peak flows were reported, with 31% of the storms events completely captured. Influent TSS loads and EMCs were well retained by all cells irrespective of treatments, storm characteristics, or seasonality. Nutrient removal was treatment-dependent, where the SM treatments consistently removed P loads and EMCs, and sometimes N as well. The vegetation and RR treatments mostly exported nutrients to the effluent. We attribute observed nutrient exports to the presence of excess compost in the soil filter media. Rainfall depth and peak inflow rate undermined bioretention performance, likely by increasing pollutant mobilization through the filter media. While the bioretention cells were a source of CO2, they varied between being a sink and source of N2O. CO2 fluxes were orders of magnitude higher than N2O fluxes. However, soil C and N, and plant C and N in biomass was seen to largely offset respiratory CO2-C and biochemical N2O-N losses from bioretention soil. The use of compost in bioretention soil media should be reduced or eliminated. If necessary, compost with low P content and high C: N ratio should be considered to minimize nutrients losses via leaching or gas fluxes. In order to understand trade-offs stemming from compost amendments, we conducted a laboratory pot study utilizing switchgrass and various organic soil amendments (e.g., different compost types and coir fiber) to a sandy loam soil contaminated with heavy metals and studied potential nutrient leaching and pollutant uptake. Addition of organic amendments significantly reduced metal bioavailability, and improved switchgrass growth and metal uptake potential. While no differences in soil or plant metal uptake were observed among the amendments, significant differences in nutrient leaching were observed.

The rapid expansion of oil palm cultivation in Southeast Asia raises environmental concerns. Oil palm growers in Indonesia are faced with the challenge of sustaining high yields to keep pace with the growing global demand for oil and fats, while reducing the environmental impacts of oil palm cultivation. Environmental impacts associated with the deforestation at the initial phase of an oil palm plantation establishment are well documented, however the impacts of mature oil palm plantation on water quality remain poorly investigated. Oil palm is a perennial crop cultivated predominantly on weathered tropical soils, so high fertilizer input is necessary to sustain high yields, which is expected to endanger neighboring aquatic ecosystems. In Indonesia, 39 % of oil palm planted area is owned by smallholder farmers, who rely on mineral fertilizers to support oil palm production, and 52 % are large private plantations operated by private industries. In addition to mineral fertilizers, industrial plantations also apply mill byproducts as organic fertilizers. Soil characteristics and fertilizer management in oil palm plantations were expected to alter the soil fertility status and nutrient loads to waterways. Oil palm plantations generally extend over thousands of contiguous hectares, so the effect of fertilizer management on the soil response and nutrient loads to waterways requires landscape-scale studies accounting for soil variability and long-term fertilization sequences across the plantation. The first objective of the thesis was to (i) perform a literature review that provides an overview of the agricultural practices in oil palm plantations as well as hydrological processes involved in the nutrient transfers to waterways. Then I aimed to (ii) assess the effect of long term mineral and organic fertilizer sequences on the soil response, considering different soil types, (iii) characterize the dominant hydrological processes involved in the nutrient fluxes to waterways, and (iv) assess the effect of fertilizer management and soil characteristics on groundwater quality and nutrient fluxes to streams. The study area was located in Central Sumatra, Indonesia, which has a tropical humid climate and weathered soils (Ferralsols). The study area was a landscape including a 4000 ha industrial plantation and a 1500 ha smallholder plantation using rational fertilizer programs. Low-fertility Ferralsols responded significantly to continuous applications of organic fertilizers, with greater improvement on coarser-textured soils, compared to repeated applications of mineral fertilizers. I proposed that spatial fertilizer management at the landscape-scale should complement the current plot-scale fertilizer management to get higher nutrient use efficiency and improve soil fertility in an oil palm plantation. One year multi-site monitoring of stream water quality showed nutrient concentrations below Indonesian standards for water quality. In this case study, mature oil palm cultivation did not contribute to the eutrophication of aquatic ecosystems. This was ascribed to nutrient dilution in streams from the high rainfall as well as high nutrient demand by oil palm that was met with a rational fertilizer program. Assessment of nutrient fluxes from baseflow showed that loamy-sand uplands were more sensitive to nutrient losses than loamy lowlands, and organic fertilization helped to reduce nutrient losses to streams. The study also showed high dissolved organic matter content in streams, likely from natural sources. Oil palm agroecosystems in the study area are characterized by fast groundwater renewal indicating the potential for inputs to be quickly transported from soils to the streams. This may be of concern when unbalanced fertilizer management leads to over-application of nutrients or persistent agrochemicals like pesticides bind to dissolved organic matter, since they will be susceptible to contribute to nonpoint source pollution in streams.
La rapide expansion de la culture du palmier à huile en Asie du Sud-Est soulève maintes interrogations sur ses impacts environnementaux. Les planteurs doivent désormais assurer de hauts rendements tout en minimisant leurs impacts. Les impacts environnementaux associés à la déforestation lors de la phase initiale d'établissement d'une plantation sont déjà bien documentés. En revanche, les impacts d'une plantation mature sur la qualité de l'eau a été très peu étudiée. Le palmier à huile est généralement cultivée sur des sols tropicaux peu fertiles d'où la nécessité de forts apports de fertilisants, apports susceptibles de menacer les écosystèmes aquatiques. En Indonésie, les petits planteurs n'utilisent que des fertilisants minéraux tandis que les industriels appliquent, en plus des fertilisants minéraux, des fertilisants organiques issus de leurs usines. Les caractéristiques du sol et la gestion de la fertilisation des palmeraies sont susceptibles d'influer sur la fertilité du sol et sur les transferts de nutriments vers les rivières. Etant donné que les plantations s'étendent généralement sur plusieurs milliers d'hectares, l'effet de la gestion de la fertilisation sur la réponse du sol et les transferts de nutriments vers les rivières nécessite des études à l'échelle du paysage. Celles-ci doivent tenir compte tant de la variabilité du sol au sein de la plantation que de la variabilité des séquences de fertilisation pluriannuelles. Le premier objectif de cette étude est (i) de réaliser une revue de littérature sur les pratiques agricoles utilisées dans les palmeraies ainsi que sur les processus hydrologiques impliqués dans les transferts de nutriments vers les rivières, (ii) d'évaluer l'effet de séquences pluriannuelles de fertilisation minérale et organique sur la réponse du sol, tenant compte de la variabilité des sols, (iii) de caractériser et quantifier les processus hydrologiques dominants impliqués dans le transfert de nutriments, (iv) et enfin d'évaluer l'effet de la gestion de la fertilisation et des caractéristiques du sol sur la qualité des eaux souterraines et sur les flux de nutriments vers les rivières. La zone d'étude est située dans le centre de Sumatra, en Indonésie. Le climat y est tropical humide et les sols peu fertiles (Ferralsols). Il s'agit d'un paysage de 100 km² incluant une plantation villageoise de 1500 ha et une plantation industrielle de 4 000 ha, pratiquant une gestion raisonnée de la fertilisation. Cette étude a montré une amélioration significative des propriétés chimiques des sols suite à des applications continues de fertilisants organiques, avec une amélioration encore plus sensible sur les sols sablo-limoneux que sur les sols limoneux. Une gestion spatiale de la fertilisation à l'échelle de la plantation devrait compléter la gestion à la parcelle pour une meilleure stratégie d'application des fertilisants adaptée à la variabilité des sols au sein de la plantation. Le suivi multi-site sur un an de la qualité des eaux de surface dans le paysage a montré des niveaux de concentrations de nutriments en deçà des limites maximales recommandées par les standards indonésiens. Dans cette étude de cas, la culture d'une palmeraie mature ne semble pas avoir contribué à l'eutrophisation des cours d'eaux. Les raisons en seraient la dilution du système par la forte pluviosité locale, et la pratique d'une fertilisation raisonnée. L'évaluation des flux de nutriments a montré que les sols sablo-limoneux étaient plus sensibles que les sols limoneux aux pertes de nutriments et que la fertilisation organique pouvait réduire significativement ces pertes. Le renouvellement rapide des eaux souterraines induit une grande réactivité du système aux intrants qui peuvent être rapidement drainés vers les cours d'eau. Des apports massifs de nutriments (fertilisation non raisonnée) ou des pesticides liés à la matière organique dissoute pourraient donc entraîner un risque de pollution en aval de l'agrosystème.

The objectives of this research were to develop and evaluate a field method for in situ measurement of soil properties using visible near-infrared reflectance spectroscopy (Vis-NIRS). A probe with an independent light source for acquiring soil reflectance spectra from soil cores was developed around an existing portable field spectrometer (ASD FieldSpecPro, Boulder, CO, USA; 350-2500 nm). Initial experiments tested the ability of the acquired spectra to predict plant root density, an important property in soil carbon dynamics. Reflectance spectra were acquired from soil containing ryegrass roots (Lolium multiflorum) grown in Allophanic and Fluvial Recent soils in a glasshouse pot trial. Differences in root density were created by differential nitrogen and phosphorus fertilization. Partial least squares regression (PLSR) was used to calibrate spectral data (pre-processed by smoothing and transforming spectra to the first derivative) against laboratory-measured root density data (wet-sieve technique). The calibration model successfully predicted root densities (r2 = 0.85, RPD = 2.63, RMSECV = 0.47 mg cm-3) observed in the pots to a moderate level of accuracy. This soil reflectance probe was then tested using a soil coring system to acquire reflectance spectra from two soils under pasture (0-60 mm soil depths) that had contrasting root densities. The PLSR calibration models for predicting root density were more accurate when soil samples from the two soils were separated rather than grouped. A more accurate prediction was found in Allophanic soils (r2 = 0.83, RPD = 2.44, RMSECV = 1.96 mg g-1) than in Fluvial Recent soils (r2 = 0.75, RPD = 1.98, RMSECV = 5.11 mg g-1). The Vis-NIRS technique was then modified slightly to work on a soil corer that could be used to measure root contents from deeper soil profiles (15- 600 mm depth) in arable land (90-day-old maize crop grown in Fluvial Recent soils). PLSR calibration models were constructed to predict the full range of maize root densities (r2 = 0.83, RPD = 2.42, RMSECV = 1.21 mg cm-3) and also soil carbon (C) and nitrogen (N) concentrations that had been determined in the laboratory (LECO FP- 2000 CNS Analyser; Leco Corp., St Joseph, MI, USA). Further studies concentrated on improving the Vis-NIRS technique for prediction of total C and N concentrations in differing soil types within different soil orders in the field. The soil coring method used in the maize studies was evaluated in permanent and recent pastoral soils (Pumice, Allophanic and Tephric Recent in the Taupo-Rotorua Volcanic Zone, North Island) with a wide range of soil organic matter contents resulting from different times (1-5 years) since conversion from forest soils. Without any sample preparation, other than the soil surface left after coring, it was possible to predict soil C and N concentrations with moderate success (C prediction r2 = 0.75, RMSEP = 1.23%, RPD = 1.97; N prediction r2 = 0.80, RMSEP = 0.10%, RPD = 2.15) using a technique of acquiring soil reflectance spectra from the horizontal cross-section of a soil core (H method). The soil probe was then modified to acquire spectra from the curved vertical wall of a soil core (V method), allowing the spectrometer’s field of view to increase to record the reflectance features of the whole soil sample taken for laboratory analysis. Improved predictions of soil C and N concentrations were achieved with the V method of spectral acquisition (C prediction r2 = 0.97, RMSECV = 0.21%, RPD = 5.80; N prediction r2 = 0.96, RMSECV = 0.02%, RPD = 5.17) compared to the H method (C prediction r2 = 0.95, RMSECV = 0.27%, RPD = 4.45; N prediction r2 = 0.94, RMSECV = 0.03%, RPD = 4.25). The V method was tested for temporal robustness by assessing its ability to predict soil C and N concentrations of Fluvial Recent soils under permanent pasture in different seasons. When principal component analysis (PCA) was used to ensure that the spectral dimensions (which were responsive to water content) of the data set used for developing the PLSR calibration model embraced those of the “unknown” soil samples, it was possible to predict soil C and N concentrations in “unknown” samples of widely different water contents (in May and November), with a high level of accuracy (C prediction r2 = 0.97, RMSEP = 0.36%, RPD = 3.43; N prediction r2 = 0.95, RMSEP = 0.03%, RPD = 3.44). This study indicates that Vis-NIRS has considerable potential for rapid in situ assessment of soil C, N and root density. The results demonstrate that field root densities in pastoral and arable soil can be predicted independently from total soil C, which will allow researchers to predict C sequestration from root production. The recommended “V” technique can be used to assess spatial and temporal variability of soil carbon and nitrogen within soil profiles and across the landscape. It can also be used to assess the rate of C sequestration and organic matter synthesis via root density prediction. It reduces the time, labour and cost of conventional soil analysis and root density measurement.