Teses / dissertações sobre o tema "Temperate pastures"

This thesis describes the research undertaken for the degree of Doctor of Philosophy, testing the hypothesis that spectrometer data can be used to establish usable relationships for prediction of pasture quality attributes. The research data consisted of reflectance measurements of various temperate pasture types recorded at four different times (years 2000 to 2002), recorded by three hyperspectral sensors, the in situ ASD, the airborne HyMap and the satellite-borne Hyperion. Corresponding ground-based pasture samples were analysed for content of chlorophyll, water, crude protein, digestibility, lignin and cellulose at three study sites in rural Victoria, Australia. This context was used to evaluate effects of sensor differences, data processing and enhancement, analytical methods and sample variability on the predictive capacity of derived prediction models. Although hyperspectral data analysis is being applied in many areas very few studies on temperate pastures have been conducted and hardly any encompass the variability and heterogeneity of these southern Australian examples. The research into the relationship between the spectrometer data and pasture quality attribute assays was designed using knowledge gained from assessment of other hyperspectral remote sensing and near-infrared spectroscopy research, including bio-chemical and physical properties of pastures, as well as practical issues of the grazing industries and carbon cycling/modelling. Processing and enhancement of the spectral data followed methods used by other hyperspectral researchers with modifications deemed essential to produce better relationships with pasture assay data. As many different methods are in use for the analysis of hyperspectral data several alternative approaches were investigated and evaluated to determine reliability, robustness and suitability for retrieval of temperate pasture quality attributes. The analyses employed included stepwise multiple linear regression (SMLR) and partial least squares regression (PLSR). The research showed that the spectral research data had a higher potential to be used for prediction of crude protein and digestibility than for the plant fibres lignin and cellulose. Spectral transformation such as continuum removal and derivatives enhanced the results. By using a modified approach based on sample subsets identified by a matrix of subjective bio-physical and ancillary data parameters, the performance of the models were enhanced. Prediction models from PLSR developed on ASD in situ spectral data, HyMap airborne imagery and Hyperion and corresponding pasture assays showed potential for predicting the two important pasture quality attributes crude protein and digestibility in hyperspectral imagery at a few quantised levels corresponding to levels currently used in commercial feed testing. It was concluded that imaging spectrometry has potential to offer synoptic, simultaneous and spatially continuous information valuable to feed based enterprises in temperate Victoria. The thesis provide a significant contribution to the field of hyperspectral remote sensing and good guidance for future hyperspectral researchers embarking on similar tasks. As the research is based on temperate pastures in Victoria, Australia, which are dominated by northern hemisphere species, the findings should be applicable to analysis of temperate pastures elsewhere, for example in Western Australia, New Zealand, South Africa, North America, Europe and northern Asia (China).

This thesis examines the hypothesis that, in southern New South Wales and northeast Victoria, Australia, palatable taxa of E. curvula offer advantages that complement those of the species that are traditionally sown in temperate pastures in a landscape context.This hypothesis was based on a review of literature showing that, prior to European settlement, the vegetation, the landscape and the climate were broadly in balance, and the wateruse pattern of the vegetation of southeastern Australia resulted in water being used more-or-less completely by the end of summer. This maximised the capacity of the soil to take up and store water during autumn and winter.Three grazing experiments and one spaced-plant species evaluation study were used to assess the role of summer-growing, C4 Eragrostis curvula in pastures in the temperate zone of southeastern Australia.Issues relating to pasture production and the productivity of wool-growing sheep were investigated. Factors affecting the sustainability of the pastures and their potential on and off site impacts were emphasised.Modelling was used to explore issues of water use, arising from the grazing experiments. It is concluded that the persistence, production, water use patterns, and the adaptability of palatable varieties of E. curvula make it a useful and complementary addition to the range of species that are currently available for use as sown pastures in southern Australia.
Doctor of Philosophy (PhD)

The goal of this work was to quantify the effects of eucalypt woodland blocks on the productivity of native pastures. This research was conducted on the Southern Tablelands of New South Wales. Tree planting or retention is seen by many as an important tool in addressing the problems of soil degradation resulting from clearing and pasture improvement that threaten the sustainability of pasture systems. In particular these are dry land salinity and erosion, both of which affect large areas of agricultural lands in the south east of Australia. Whilst native tree cover remains over substantial portions of Australian pasture lands, mainly on steeper slopes and poorer soils, little has been done to measure the effects of trees on pasture productivity and soil fertility on the Southern Tablelands. Previous studies in other areas have shown a range of effects�from facilitation to inhibition�of pasture growth in the presence of trees. Soil fertility beneath trees has been shown by a number of workers to be elevated in comparison with situations in the open. Given that the range of effects may be highly site dependent, application of results from one area to another may not be valid. Thus it is necessary to measure tree effects on a regional scale if results are to be reliable. Pasture productivity was assessed over a two year period on four sites in the vicinity of Bungendore, New South Wales. A pair of plots was selected on each site, one plot in a block of eucalypt woodland, and the other nearby in an exposed, open situation. Plots were chosen to be as similar to each other as possible with the exception of tree cover. Treed plots had a tree basal area of between 10 and 20 m2 ha-1 and plots had an area of 900 m2. Two of the sites were on granitic soils and had a tree cover consisting predominantly of Eucalyptus pauciflora. The remaining two sites were on soil derived from sedimentary rocks with tree cover consisting mainly of E. mannifera, E. dives and E. melliodora. Perennial native pasture species present were similar across all sites, although their relative contributions to standing biomass varied between sites. As the plots were grazed during the period of measurement, productivity and offtake were measured seasonally using exclosure cages on each plot. Pasture standing biomass was assessed using the comparative yield technique. Microclimate was monitored in each plot by automatic weather stations. Soil moisture to a depth of 45 cm was measured by time domain reflectometry using permanent probes in each plot. Ten additional survey plots on each site, covering the range of tree basal area from 0 - 30 m2 ha-1, were assessed each season in the second year for standing biomass, soil fertility and pasture quality; expressed by nitrogen content and dry matter digestibility. Pasture floristics were measured using the dry-weight-rank method. These additional plots were chosen to be as representative of the paddocks as possible. Over the two years that productivity was measured, it was found to be higher under trees than in the open. This was predominantly due to higher winter and spring growth within treed plots. Grazing offtake was also found to be higher under trees, partly accounting for lower standing biomass found in the treed plots. Wind run, evapotranspiration and photosynthetically active radiation were all reduced by the presence of trees. Beneficial effects of shelter from winds may largely explain the higher productivity observed in the treed plots, and could outweigh negative effects of below ground competition and radiation interception by tree canopies at low to moderate tree densities. Soil moisture was not affected by the presence of trees. Soil fertility also did not differ between treed and open plots nor was there any difference in pasture nitrogen content or dry matter digestibility. On the sites where soils were derived from sedimentary rocks, pasture floristics were found to be related to tree basal area. Themeda ausfralis biomass was negatively related to tree basal area, and was partially replaced by large tussock species such as Poa sieberiana and Chionochloa pallida. A reduction of pasture quality resulted, particularly as the latter species is not grazed to any significant extent. Given the desirability of having deep rooted perennial components in grazing lands, the results of this study indicate that it may be possible to utilise trees to assist in preventing or reducing a range of adverse environmental consequences arising from agricultural activities, without unduly compromising pasture productivity. Additionally, the wide range of environmental conditions provided by a mix of treed and open pasture promotes a higher degree of heterogeneity of the herbaceous layer. This may assist in maintaining productivity over a greater range of climatic conditions than would be the case with a more homogeneous pasture.

Climate change is likely to alter plant species composition and interactions between plants and soil microbes that together dictate the quantity and quality of forage produced in pastures, the base of animal production in central Kentucky. This study assessed the seasonal dynamics of soil microbes and their response to increased temperature (+3oC) and growing season precipitation (+30% of the mean annual). Total soil microbial biomass, community composition, enzyme activities, potential carbon mineralization, and catabolic responses to selected substrates were measured seasonally in the different climate treatments. In this system, seasonal variability was a dominant driving factor for all the soil microbial characteristics that I investigated. Summer maxima and winter minima were identified in the active microbial biomass, while soil microbial community structure differed between each season. Extracellular enzyme activities were generally highest in either the spring or summer, while seasonal patterns for each substrate were unique across catabolic response profiles. Climate treatments produced few significant main or interactive effects on the soil microbial biomass and function. This resiliency, coupled with evidence of functional redundancy, suggests that central Kentucky pasture ecosystems may be well-equipped to handle future environmental stress associated with climate change and to maintain critical ecosystem services.

This thesis is about the dynamics of eastern grey kangaroo (Macropus giganteus) populations and their food supplies in temperate grasslands of south-eastern Australia. It is based on the study of three populations of eastern grey kangaroos inhabiting �warm dry�, �cold dry�, and �warm wet� sites within the Southern Tablelands climatic region. After a pilot survey and methods trial in early 2001, the main period of study was from August 2001 to July 2003. The study populations were found to have the highest densities of any kangaroo populations, 450 to 510 km-2. Their density was the same at the end of the two year study period as at the beginning, in spite of a strong decline in herbage availability due to drought. The eastern grey kangaroo populations were limited according to the predation-sensitive food hypothesis. Fecundity, as the observed proportion of females with late pouch young in spring, was high, in spite of the high kangaroo density and restricted food availability. Age-specific fecundity of a kangaroo sample shot on one of the sites in 1997 to avert starvation was the highest reported for kangaroos. Thus, limitation acted through mortality rather than fecundity. Population growth rate was most sensitive to adult survival but the demographic rate that had the greatest effect in practice was mortality of juveniles, most likely sub-adults. The combination of high fecundity with high mortality of immatures would provide resilience to low levels of imposed mortality and to fertility control. The normal pattern of spring pasture growth was not observed in the drought conditions and few of the recorded increments of growth were of the magnitude considered typical for sites on the southern and central tablelands. Temperature was necessary to predict pasture growth, as well as rainfall, over the previous two months. The best model of pasture growth (lowest AICc) included negative terms for herbage mass, rainfall over the previous two months, and temperature, and a positive term for the interaction between rainfall and temperature. It accounted for 13% more of the variation in the data than did the simpler model of the type used by Robertson (1987a), Caughley (1987) and Choquenot et al. (1998). However this was only 63% of total variation. Re-evaluation of the model based on measurements of pasture growth in more typical (non-drought) conditions is recommended. Grazing had a powerful influence on the biomass of pasture due to the high density of kangaroos. This is a marked difference to many other studies of the type which have been conducted in semi-arid environments where rainfall dominates. The offtake of pasture by kangaroos, as estimated on the research sites by the cage method, was linear on herbage mass. It was of greater magnitude than the more exact estimate of the (curved) functional response from grazedowns in high�quality and low�quality pastures. The widespread recognition of three forms of functional response is inadequate. Both the theoretical basis, and supporting data, have been published for domed, inaccessible residue, and power forms as well (Holling 1966; Noy-Meir 1975; Hassell et al. 1976, 1977; Short 1986; Sabelis 1992). Eastern grey kangaroos had approximately the same Type 2 functional response when consuming either a high quality artificial pasture (Phalaris aquatica), or dry native pasture (Themeda australis) in autumn. Their functional response rose more gradually than those published for red kangaroos and western grey kangaroos in the semi-arid rangelands, and did not satiate at the levels of pasture available. This gradual behaviour of the functional response contributes to continuous stability of the consumer-resource system, as opposed to discontinuous stability. The numerical response was estimated using the ratio equation, assuming an intrinsic rate of increase for eastern grey kangaroos in temperate grasslands of 0.55. There is indirect evidence of effects of predation in the dynamics of the kangaroo populations. This is demonstrated by the positive relationship between r and kangaroo density. Such a relationship can be generated by predation. A desirable future task is to compile estimates of population growth rate and simultaneous estimates of pasture, in the absence of predation, where kangaroo population density is changing, so that the numerical response can be estimated empirically. The management implications arising from this study are numerous and a full account would require a separate report. As one example, kangaroos in these temperate grasslands are on average smaller, eat less, are more numerous, and are more fecund, than would be predicted from other studies (e.g. Caughley et al. 1987). Thus the benefit of shooting each kangaroo, in terms of grass production, is less, or, in other words, more kangaroos have to be shot to achieve a certain level of impact reduction, and the population will recover more quickly, than would have been predicted prior to this study. Secondly, of much importance to managers, the interactive model which can readily be assembled from the products of Chapters 4, 5 and 8, can be used to test a range of management options, and the effect of variation in weather conditions, such as increased or decreased rainfall. For example, the model indicates that commercial harvesting (currently under trial in the region), at the maximum level allowed, results in a sustainable harvest of kangaroos, but does not increase the herbage mass, and only slightly reduces the frequency of crashes when herbage mass falls to low levels. (To demonstrate this with an ecological experiment would require an extremely large investment of research effort.) However, an alternative �national park damage mitigation� formula, which holds kangaroo density to about 1 ha-1, is predicted to increase herbage mass considerably and to reduce the frequency of crashes in herbage mass, but these effects would be achieved at the cost of having to shoot large numbers of kangaroos. Thus, aside from many specific details of kangaroo ecology, the knowledge gained in this study appears to have useful potential to illustrate to managers the dynamic properties of a resource-consumer system, the probabilistic nature of management outcomes, and the consequences of particular kangaroo management proposals.

Current research looked into the effects of supplementing essential amino acids L-lysine and DL-methionine to lactating dairy cows, grazing annual ryegrass and receiving a low protein concentrate meal. Twenty Holstein cows were managed in a 2x2 crossover experimental design, with two treatments and two periods. Cows received the same diet in both treatments, except for the inclusion of 20g lysine and 60g methionine in one treatment. This aimed at supplying 6.92% and 2.34% of the metabolizable protein in lysine and methionine, respectively, as suggested by the Cornell Net Carbohydrate and Protein System (CNCPS). No significant differences were found in milk (36,19 vs. 35,97kg), total crude protein (1,14 vs. 1,15kg) and lactose (1,62 vs. 1,66kg) yields, casein content (2,55 vs. 2,55%), somatic cell count (309 vs. 363cél.mL-1), milk urea nitrogen (12,40 vs. 12,15mg.dL-1), and blood urea (25,01 vs. 25,09mg.dL-1) for the control and the amino acid supplemented treatments, respectively. The amino acid supplemented treatment presented a lower milk fat content (3,58 vs. 3,39%), but no differences yield (1,29 vs. 1,21kg), which led to the same 4% milk fat corrected milk yield (33,8 vs. 32,6kg). The lower milk fat content resulted in a lower total milk solids content (12,56 vs. 12,26%) in the amino acid supplemented treatment, in spite of this treatment presenting similar crude protein (3,17 vs. 3,20%) and lactose (4,48 vs. 4,61%) contents. Animals receiving the amino acid supplementation also presented lower creatinine blood (0,74 vs. 0,89mg.dL-1) suggesting a lower muscle tissue mobilization, in spite of their similar urine urea nitrogen test (264,15 vs. 351,30 mg.dL-1) and urine creatinine (42,46 vs. 38,04mg.dL-1). Rumen-protected lysine and methionine supplementation did not affect milk yield but did affect milk composition and reduced serum creatinine.
Neste trabalho, avaliou-se os efeitos da adição dos aminoácidos essenciais L-lisina e DL-metionina na dieta de vacas em lactação, mantidas em pastagens de azevém anual e suplementadas com concentrado de baixo teor proteico. Foram utilizadas 20 vacas da raça holandesa em um delineamento experimental crossover (2x2), submetidas a dois tratamentos e dois períodos. Ambos tratamentos receberam dietas iguais, com exceção da inclusão ou não de 20 e 60g dos aminoácidos lisina e metionina, respectivamente, buscando atingir os níveis de 6,92% de lisina e 2,34% de metionina na proteína metabolizável, sugeridos pelo Cornell Net Carbohydrate and Protein System (CNCPS). Não foram encontradas diferenças significativas para produção de leite (36,19 vs. 35,97kg), produção total de proteína bruta (1,14 vs. 1,15kg) e de lactose (1,62 vs. 1,66kg), teor de caseína (2,55 vs. 2,55%), contagem de células somáticas (309 vs. 363cél.mL-1), nitrogênio ureico no leite (12,40 vs. 12,15mg.dL-1) e ureia no sangue (25,01 vs. 25,09mg.dL-1) para os grupos controle e com adição de lisina e metionina, respectivamente. O grupo que recebeu a suplementação apresentou menor teor de gordura no leite (3,58 vs. 3,39%), mas igual volume de gordura produzido (1,29 vs. 1,21kg), não interferindo na produção de leite quando esta variável foi corrigida para 4% de gordura (33,8 vs. 32,6kg). O teor menor de gordura fez com que o teor de sólidos totais fosse menor no grupo que recebeu os aminoácidos (12,56 vs. 12,26%), embora este tenha apresentado teor igual de proteína (3,17 vs. 3,20%) e superior de lactose (4,48 vs. 4,61%). Os animais que receberam os aminoácidos também apresentaram teores inferiores de creatinina no sangue (0,74 vs. 0,89mg.dL-1) sugerindo uma mobilização menor de tecidos musculares, embora tenham apresentado níveis semelhantes de ureia na urina (264,15 vs. 351,30 mg.dL-1) e creatinina na urina (42,46 vs. 38,04mg.dL-1). O fornecimento dos aminoácidos lisina e metionina protegidos na degradação ruminal, não influenciou a produção total de leite, mas sim sua composição, além de reduzir os níveis de creatinina sérica.

This research examined the mechanisms by which temperature, water availability and nitrogen (N) affect the dry matter (DM) yield potential of cocksfoot (Dactylis glomerata L.) dominant pastures. The experiment was a split plot design with main plots of fully irrigated (I) or dryland (D), sub-plots of N fertiliser at 800 kg N/ha in 2003/04; and 1600 kg N/ha in 2004/05 (+N) or 0 kg N/ha (-N). The potential environmental yield of an established 8 year old cocksfoot dominant pasture was 21.9 t DM/ha/y from I+N pastures compared with 9.8 t DM/ha by I-N pastures and 15.1 t DM/ha/y by D+N pastures. The lowest yields were from dryland pastures with no N which produced 7.5 t DM/ha/y in 2003/03 and 5.0 t DM/ha/y in 2004/05. The effect of seasonal temperatures on the DM production, when periods of water stress were excluded, was quantified using thermal time accumulated above a base temperature of 3°C as 7.0 kg DM/°Cd/ha for N fertilised pastures and 3.3 kg DM/°Cd/ha for pastures with no N. The 2.5 t DM/ha difference in yields of D-N pastures in 2003/04 and 2004/05 was the result of the duration, extent and timing of the water stress period. In both years the critical limiting deficit (DL) was calculated as 78 mm from the soil moisture deficit in the 0-0.8 m soil layers. Beyond DL yield decreased at a rate of 1.45%/mm in +N and –N pastures, relative to fully irrigated control pastures. Yields of D+N and D-N pastures were similar during periods of water stress with 0.4±0.1 t/DM/ha produced during the rotation ending 30/12/2003. This was less than from either the I-N (1.2 t DM/ha) or I+N (3.5 t DM/ha) pastures due to the reduction in the amount of photosynthetically active radiation intercepted by the canopies of the dryland pastures. However, in the rotation ending 2/5/2004, after autumn rain alleviated drought conditions, yield of the D+N pasture was 2.1 t DM/ha compared with 1.7 t DM/ha by I+N pastures. The effect of N on yield was described using a nutrition index which showed that as DM yield increased N% in the herbage declined. This is a function of the ratio between metabolic and structural N requirements rather than caused by ontogeny alone. Specific leaf N was determined at two harvests and appeared constant at a given point in time (1.0-1.6 g N/m² leaf). In contrast, specific pseudostem N increased from 0.8-1.0 g N/m² pseudostem at an NNI of 0.4 in –N pastures to 2.6-3.0 g N/m² pseudostem at an NNI of 1.2 in the +N pastures. Differences between the yields of +N and –N pastures were caused by differences in radiation use efficiency (RUE) as determined by the linear relationship (R²=0.76) between RUE and the nitrogen nutrition index (NNI). In this thesis, empirical relationships for the effects of temperature, water availability and N were derived and the physiological mechanisms which underlie these descriptions were identified. These relationships provide clear and simple explanations of the effects of environmental variables on the productivity of cocksfoot based pastures which will enhance understanding of the benefits and limitations of cocksfoot, particularly in dryland farming systems.

New Zealand is dominated by its agricultural industry with one of the most intensive farming practices being that of intensive dairying. New Zealand currently has approximately 5.3 million dairy cows that excrete up to 2.2 L of urine, per urination event, up to 12 times per day. This equates to 5.1 x10¹⁰ L per year or enough urine to fill over 1.2 million milk tankers. This sheer volume of urine and its associated N content has implications for the cycling of N within the pasture soils utilised, and New Zealand’s greenhouse gas budget due to the emission of N₂O from urine affected areas. The emission of nitric oxide (NO) from agricultural systems is also receiving increasing attention due to concerns about alterations in the balance of atmospheric trace gases and sinks. Worldwide there is a dearth of information with respect to the emissions of NO from urine-N deposition onto soils with only two in situ studies and no studies on the effects of soil pH, environmental variables or urine-N rate on NO fluxes. This present study has provided some fundamental information on the factors and processes affecting the emission of NO from bovine urine applied to pasture soils. Five experiments were performed in total; three laboratory experiments and two field experiments. The first laboratory experiment (chapter 4) examined the effect of the initial soil pH on NOx emissions from urine-N applied at 500 kg N ha⁻¹. Soil was treated to alter the initial soil pH over the range of 4.4 to 7.6. Initial soil pH affected rates of nitrification which in turn affected the decline in soil pH. Emissions of NO increased with increasing soil pH. However, a strong positive linear relationship was established between the NO-N flux, expressed as a percentage of the net NH4⁺-N depletion rate, and the level of soil acidity. The NO-N fluxes were higher under the more acidic soil conditions where N turnover was lower. The fluxes of N₂O did not follow the same pattern and were attributed to biological mechanisms. In experiment two (chapter 5) the objectives were to concurrently examine the effects of varying the soil temperature and the water-filled pore space (WFPS) on NOx emissions from urine-N. In this experiment increasing the soil temperature enhanced both the rate of nitrification and the rate of decrease in soil pH. The relationship between the net NO-N flux, expressed as a percentage of the net NH4⁺-N depletion rate, and the level of soil acidity was again demonstrated at the warmest soil temperature (22°C) where soil acidification had progressed sufficiently to enable abiotic NO formation. The NO-N fluxes increased with decreasing soil moisture and increasing soil acidity indicating abiotic factors were responsible for NO production. The Q10 response of the NO flux between 5 to 15°C decreased from 4.3 to 1.5 as WFPS increased from 11% to 87% respectively. Fluxes of N₂O increased with increasing WFPS and temperature indicating that denitrification was the dominant process. Results from experiments 2 and 3 indicated that the rate of nitrification had a direct bearing on the ensuing soil acidity and that it was this in conjunction with the available inorganic-N pools that affected NOx production. Therefore the third experiment examined the effect of urine-N rate on NOx emissions, with urine-N rate varied over 5 levels from 0 to 1000 kg N ha⁻¹, the highest rate being that found under maximal urine-N inputs to pasture. Rates of nitrification were diminished at the highest rates of urine-N applied and decreases in soil acidity were not as rapid due to this. Again significant but separate linear relationships were developed, for each urine-N rate used, between the NO-N flux, expressed as a percentage of the net NH4⁺-N depletion rate, and the level of soil acidity. The slope of these relationships increased with increasing urine-N rate. The NO-N flux, expressed as a percentage of the net NH4⁺-N depletion rate, versus soil acidity was higher under 1000 kg N ha⁻¹, despite the lower soil acidity in this treatment. This indicated that the enhanced inorganic-N pool was also playing a role in increasing the NO flux. The N₂O fluxes were of limited duration in this experiment possibly due to conditions being disadvantageous for denitrification. In the field experiments two urine-N rates were examined under both summer and winter conditions at two urine-N rates. The emission factors after 71 days for NO-N in the summer were 0.15 and 0.20% of the urine-N applied for the 500 and 1000 kg N ha⁻¹ rates respectively while the respective N₂O-N fluxes were 0.14 and 0.16%. Under winter conditions the emission factors after 42 days for NO-N were <0.001% of the urine-N applied regardless of urine-N rate while the N₂O-N fluxes were 0.05 and 0.09% for the 500 and 1000 kg N ha⁻¹ urine-N rates respectively. The relationships and predictors of NO-N flux determined in the laboratory studies did not serve as strong indicators of the NO-N flux under summer conditions. Low emissions from urine-N over winter were due to the low soil temperatures and high WFPS. These studies have demonstrated that soil chemical and environmental variables influence the production of NOx and N₂O emissions from urine-N applied to soil and that seasonal effects have a significant impact on the relative amounts of NO-N and N₂O-N emitted from urine patches. Suggestions for future work are also made.

Thesis (MSc. (Pasture Science)) -- University of Limpopo, 2016
South Africa is regarded as a semi-arid area; only 28% of the country receives more than 600 mm rainfall recorded annually. Sustainable utilization of cool season fodder grasses in summer rainfall areas to produce winter animal feed remains a major problem. Farmers are affected by a shortage of adequate, good quality herbage for livestock during winter and dry periods on commercial farms. The study aimed to evaluate and compare the production potential of six Festulolium hybrids, three Dactylis species, and five Lolium hybrids and three grass-legume mixtures in the summer rainfall area. A total of 17 cultivars were evaluated for their DM production under the treatment of different fertilizer levels on three planting dates (16 March 2011, 21 April 2011 and 4 April 2012). The study was carried out at Hygrotech Seed Company (Experimental site), Dewagensdrift in Moloto Village outside Pretoria in the Gauteng Province. Data was collected on a monthly basis from sub-plots of 1 m x 1 m (m2) in 51 plots of 1.5 m x 6 m (9 m2), with nine rows that were 10 cm apart arranged under RCBD with three replicates per cultivar. Harvested fresh samples were taken, weighed, dried at 60ºC until they reached a constant dry weight and weighed to determine DM content. A Fischer’s protected LSD at the 5 % level was performed to compare the treatment means. Over a period of three years of study, it shows that the low fertilizer level resulted in the lowest DM production, with no significant difference occurring between medium and high fertilizer levels. To achieve optimum DM production with minimum cost medium fertilizer is recommended. The cultivars responded differently to the three different planting dates. The time of planting had an effect on DM production in winter. It is recommended that Festulolium hybrids and Lolium hybrids be planted earlier (March) for better DM production in winter.
National Research Foundation (NRF)

In New Zealand, native shrubs are considered an important potential carbon-sink in disturbed or abandoned land (e.g., pastoral land that is unsustainable for long-term pastoral agriculture). However, the impact of varying environmental drivers on carbon uptake from photosynthesis and carbon loss from respiration of a developing shrubland remains uncertain. In this study, the effects of both temperature and soil water content (θ) on photosynthesis and respiration were examined under controlled growth cabinet and field conditions in a pasture grass and the native shrub, kānuka (Kunzea ericoides var. ericoides). The purpose of the investigation was to assess the combined impacts of varying temperature and θ on canopy processes and to disentangle the effects of θ on photosynthesis and respiration for the two different plant types. A controlled growth cabinet study (Chapter 2) showed that θ had a greater effect on the short-term temperature response of photosynthesis than the temperature response of respiration. The optimum value of θ for net photosynthesis was around 30 % for both kānuka and the grass. Statistical analysis showed that the temperature sensitivity of photosynthetic parameters was similar for both plant types, but the sensitivity of respiratory parameters was different. Reduction in θ induced an inhibition of photosynthetic capacity in both plant types. The response of respiratory parameters to θ was not related to substrate limitations, however available evidence suggests that it is likely to be a species dependent plant mechanism in regulating the cost of maintenance due to reduced photosynthate assimilation and decreasing energy supply to support the activity of respiratory enzymes. Results obtained from a field study (Chapter 3) showed that photosynthesis and respiration in the grass and kānuka were sensitive to seasonal changes in temperature and θ. Photosynthetic parameters showed little acclimation following changes in seasonal growth conditions. In contrast, respiratory parameters tended to acclimate more strongly. Respiratory acclimation to multiple environmental conditions was characterised by changes in temperature sensitivity and a shift in the response of respiration to temperature, demonstrating the involvement of both ‘Type I’ and ‘Type II’ acclimation in both plant types. The results from controlled growth cabinet and field studies were used to drive a leaf level model that integrates the responses of photosynthesis and respiration to changes in temperature and θ and incorporates acclimation using variable photosynthetic and respiratory parameters (Chapter 4). This model was used to estimate the annual canopy carbon exchange of the grass and kānuka in response to seasonal changes and to predict changes in canopy carbon exchange under varying future climate change scenarios. The model highlighted the importance of considering seasonally-acclimated parameters in estimating canopy carbon exchange of both plant types to concurrent changes in multiple environmental variables. The overall results support the conclusion that understanding the combined effects of environmental variables on canopy processes is essential for predicting canopy net carbon exchange of a pasture-shrub system in a changing global environment. It has been shown here that the rate of increase in photosynthesis with increasing θ is greater than that of respiration which results in a progressively greater apparent carbon gain at moderate values of θ. Moreover, the impact of lower values of θ, which reduced the apparent sensitivity of respiration to temperature, may effectively decrease the rate of respiration during warmer summer months and enhance thermal acclimation via downregulation of respiration. Therefore, considering the influence of soil water conditions on the temperature sensitivity of photosynthetic and respiratory model parameters has important implications for precisely predicting the net carbon exchange of a pasture-shrub system.

The vegetative and reproductive development of balansa clover (Trifolium michelianum Savi.) were quantified in relation to the environmental drivers of each phenophase in field and controlled environments. In a grazed experiment over 6 years, balansa clover sown with cocksfoot (Dactylis glomerata) contributed 1.6 t DM/ha/year, or ~20% of the total DM production. However, grazing management for increased seed production during flowering in the establishment year strongly influenced balansa clover regeneration. The earliest closed plot (September) averaged between 2.2 and 4.3 t DM/ha/year of balansa clover across all six years. In an incubator, balansa clover required 29°Cd for germination with an optimum temperature of 14°C and a maximum of 40°C. The base temperature for germination was 0°C. A field experiment determined that 38°Cd were required for emergence with an optimum soil temperature (Topt) of 8.5°C. The time from emergence until the first leaf appeared, the phyllochron and timing of axillary leaf appearance were compared with perennial ryegrass (Lolium perenne) and white clover (Trifolium repens L.). The rate of each was found to increase linearly with temperature. The balansa clover cultivar ‘Frontier’ required 97°Cd from sowing for the first leaf to appear, had a phyllochron of 47°Cd and secondary leaves appeared after 490°Cd. For each vegetative stage, the base temperature was 2.5°C. The timing of flower appearance depended on the quantity and direction of change of the photoperiod at emergence. A balansa clover plant, cv. ‘Bolta’, which emerged on 1 December into an increasing photoperiod of 15.6 hours flowered after 574°Cd (Tbase = 2.5°Cd) or 58 days after emergence. In contrast, if the plant emerged on 16 January into a similar but decreasing photoperiod it took 1503°Cd or 227 days to flower. This length of time became progressively shorter until remaining constant after the shortest day. In contrast, ‘Frontier’ took a constant 390 and 690 °Cd in increasing and decreasing photoperiods, respectively. The time which an individual inflorescence took from pollination until seeds were physiologically mature was 250 °Cd for both ‘Bolta’ and ‘Frontier’. The re-establishment of balansa clover each year relied on a large seed set (>1000 kg/ha) in the establishment year. The continued survival of balansa clover would then depend on a similar seeding event within a 4-5 year period to maintain the seed bank. Management considerations for balansa clover persistence and survival are discussed.

Este estudo teve como objetivo avaliar e quantificar o efeito do sombreamento artificial proporcionado por diferentes tipos de materiais de cobertura sobre a fisiologia, o comportamento e o desenvolvimento de novilhas leiteiras, em ambiente de pastagens. A pesquisa foi realizada no período de 08/01/2007 à 30/04/2007. A área experimental foi dividida em 16 parcelas adjacentes e iguais com 84 m² cada. Foram comparados a testemunha (sem sombra) com três tipos de cobertura: telhas de fibrocimento sem cimento amianto, telhas galvanizadas e tela de polipropileno 80% As dimensões dos abrigos foram 2m x 4m e 4m de altura (4m² de sombra.animal-1), sem paredes laterais. Foram utilizadas 16 novilhas Holandesas e 16 Hol x Jersey com idade e peso iniciais de 17,2 ± 5,6 meses e 265,3 ± 66,9kg, respectivamente, pareadas em função da uniformidade de peso e idade. As novilhas permaneciam em piquetes de capim elefante (Penissetum purpureum) durante a noite e após as 9:00h eram conduzidas para as parcelas. A tgn foi registrada por minidatalogger conectado a globo negro para cálculo de CTR e ITGU em cada parcela. As variáveis meteorológicas foram obtidas no posto agrometeorológico da ESALQ/USP. Semanalmente foram registradas FR, TR e TP. As observações comportamentais foram realizadas em dias não consecutivos por 24 horas pelo método focal. As pesagens dos animais foram realizadas mensalmente. As condições ambientais durante o período da pesquisa foram caracterizadas como estressantes para novilhas. A análise física dos materiais (tgn, CTR e ITGU) indicou diferença entre os materiais de cobertura (P<0,05) sendo a telhas de fibrocimento sem amianto a mais confortável termicamente, seguida da telha galvanizada e da tela. Os valores de FR foram menores sob as telhas de fibrocimento (P<0,05) e semelhantes entre telha galvanizada e tela (P>0,05), os valores de TR não apresentaram diferença entre tratamentos somente entre horários e para a TP houve diferença (P<0,05) entre o tratamento fibrocimento e a testemunha, porém não houve entre os demais (P>0,05). A FR apresentou as respostas mais imediatas às alterações ambientais. Houve correlação da TR com a FR e a TP. Não foram observadas alterações comportamentais entre os tratamentos, os animais ficaram sob as sombras nas horas mais quentes do dia, preferencialmente em pé, o comportamento diário seguiu os padrões conhecidos para bovinos. O ganho de peso não foi alterado pelos tratamentos. A análise de custo indicou a cobertura de fibrocimento como a mais indicada para a construção de abrigos considerando-se os resultados encontrados. A pesquisa indicou haver melhora no bem estar térmico das novilhas, porém, não conseguiu determinar ganhos efetivos na utilização da sombra.
The objective of the present study was to evaluate and quantify the effect of artificial shade given by different types of roofing materials on the physiology, behavior and development of dairy heifers in a pasture environment. The present study took place from January 8, 2007 to April 30, 2007. The experimental area was divided into 16 equal, adjacent plots with 84 m2. Three roofing treatments (fiber-cement roofing tiles without amianthus, galvanized roofing tiles and 80% polypropylene screen) were compared to a control (no shade). Shelter structures had no lateral walls and measured 2m x 4m x 4m height (4m² shaded per animal). Animals consisted of 16 Holstein heifers and 16 Holstein x Jersey heifers with initial age and weight being 17.2 ± 5.6 months and 265.3 ± 66.9 kg, respectively. Animals were equally distributed among the treatments according to weight and age. At night, heifers were kept in fields with Pennisetum purpureum, also known as elephant grass. After 9:00 am, animals were taken to the experimental plots. Black globe thermometer temperature (tbg) was measured using a mini-datalogger connected to a black globe. Values were then used to calculate Radiant Thermic Load (RTL) and Black Globe Humidity Index (BGHI) of each plot. Meteorological variables were obtained from the agricultural-meteorological post at the ESALQ/USP. Respiration rate (RR), rectal temperature (RT) and skin temperature (ST) were registered weekly. Behavioral observations were recorded every other day using the focal method. Animals were weighed monthly. Environmental conditions during the research period were characterized as stressful for the heifers. Physical analysis of the material (tbg, RTL and BGHI) indicated the roofing treatments to be significantly different (P<0.05), with the fiber-cement roofing tiles without amianthus to be the most comfortable regarding temperature, followed by the galvanized roofing tiles and the 80% polypropylene screens. Respiration rate was lower under the fiber-cement roofing tiles (P<0.05) and similar under the galvanized tiles and polypropylene screen (P>0.05). RR values were lower under the fiber-cement tiles (P<0.05) and similar under the galvanized roofing tiles and polypropylene screen (P>0.05). There were no significant differences in RT values among treatments; however, a difference was found among data collection times. Concerning ST, fiber-cement tiles were significantly different from the control (P<0.05). On the other hand, there were no significant differences regarding ST among the other treatments (P>0.05). RR presented the most immediate response to environmental alterations. RT presented correlation with RR and ST. No behavioral alterations were observed among the treatments. Daily behavior followed known bovine patterns. Weight gain was not altered by the treatments. A cost analysis indicated fibercement roofing tiles to be better for shelter construction. The present study also indicated improved heifer thermal well-being; however, no effective gains could be determined from shade use.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
This work was divided in two experiments. In first the objective was to evaluate the carcass, meat, carcass no integrants components and fatty acids profile of intramuscular fat of Devon steers finished in: feedlot (CONF), or winter pasture (pasture of ryegrass - Lolium multiflorum Lam -PTEM), or tropical pasture (association of millet pasture - Pennisetum americanum (L.) Leeke and alexander grass Brachiaria plantaginea - PTRO). At the beginning of finishing the average weight of steers was 320 kg and age was 15 months. The roughage:concentrate ratio from CONF was 60:40. The finishing in feedlot and winter pasture showed lower slaughter age in relation to finishing in tropical pasture, resulting in carcass of better quality. The animals finished in winter pasture showed meat more black and lower tenderness in relation to CONF or PTRO. However, the PTRO animals showed lower palatability. The feeding system affect the carcass no integrants components, principally the absolute and relative of liver, total weight of all internal organs, rumen-reticulum, heart fat and intestines fat that were higher from PTEM. The absolute and relative weight of blood and omasum were higher from CONF. The tract gastrointestinal content weight was higher from PTRO. Theses differences must be taken into account when calculating nutrition requirements for animals in finishing. The finishing in winter pasture show meat with intramuscular fat more beneficial in comparison to finishing in feedlot, principally by higher contents of CLA, ω-3 total and lower ω-6/ω-3 ratio. The finishing in tropical pasture resulted in meat with nutritional values intermediaries to PTEM and CONF. In the second experiment the objective was to evaluate the changes of fatty acids profile intake and duodenal digest of steers fed with diets different: Conventional = diet typical of feedlot (60% of maize silage and 40% of concentrate); winter pasture silage (pasture of ryegrass - Lolium multiflorum Lam), or tropical pasture silage (association of millet pasture - Pennisetum americanum (L.) Leeke and alexander grass Brachiaria plantaginea). Six steers crossbreds Charolais x Nellore with cannulas in duodenum were used, in a 3 x 3 double Latin square design. The conventional diet show higher changes of fatty acids profile intake to fatty acids profile duodenal digest, principally in saturated and polyunsaturated fatty acids. The presence de concentrated in diet stimulated production of vacenic acid in duodenal digest, however inhibited the production of CLA
O trabalho foi dividido em dois experimentos. No primeiro experimento o objetivo foi avaliar as características da carcaça, da carne, dos componentes não-integrantes da carcaça e o perfil de ácidos graxos da gordura intramuscular de novilhos Devon terminados em confinamento (CONF) ou em pastagem temperada (pastagem de azevém - Lolium multiflorum Lam -PTEM) ou em pastagem tropical (associação de pastagem de milheto - Pennisetum americanum (L.) Leeke e capim papuã Bracharia plantaginea - PTRO). No início da terminação os novilhos apresentaram em média 320 kg e 15 meses de idade. Os animais confinados foram alimentados com relação volumoso:concentrado de 60:40. A terminação em confinamento e em pastagem temperada possibilitou a redução da idade de abate em comparação a terminação em pastagem tropical, proporcionando carcaças de melhor qualidade. Animais terminados em pastagem temperada apresentaram carne mais escura e com menor maciez em relação aos terminados em confinamento ou em pastagem tropical. No entanto, estes últimos apresentaram carne de menor palatabilidade do que os outros sistemas de terminação. O sistema de alimentação influenciou os componentes não integrantes da carcaça, principalmente os pesos absolutos e relativos do fígado, do conjunto de órgãos internos, do rúmen-retículo, da gordura do coração e da gordura dos intestinos que foram maiores em animais terminados em pastagem temperada. Os pesos absolutos e relativos de sangue e omaso foram maiores nos animais terminados em confinamento. O peso do conteúdo do trato gastrintestinal foi maior em novilhos terminados em pastagem tropical. A terminação em pastagem temperada proporcionou carne com gordura intramuscular mais benéfica que a terminação em confinamento, principalmente pelos maiores teores de CLA, de ácidos graxos ω-3 e menor relação ω-6/ ω-3. A terminação em pastagem tropical resultou em carne com valores nutricionais intermediários entre a pastagem temperada e o confinamento. No segundo experimento o objetivo foi avaliar as modificações do perfil de ácidos graxos pela fermentação ruminal em novilhos recebendo diferentes dietas: Convencional = dieta típica de confinamento, representada por 60% de silagem de milho e 40% de concentrado; STEM = silagem de forrageira temperada - azevém (Lolium multiflorum Lam) e STRO = silagem de forrageira tropical associação de milheto (Pennisetum americanum (L.)) + papuã (Brachiaria plantaginea). Foram utilizados seis novilhos mestiços Charolês x Nelore canulados no duodeno, em um duplo quadrado latino 3 x 3. A dieta convencional apresentou as maiores modificações do perfil de ácidos graxos do alimento em relação ao perfil apresentado na digesta duodenal. A presença de concentrado estimulou a presença de ácido vacênico na digesta duodenal, no entanto reduziu a formação de CLA.

Bien que les champignons mycorhiziens arbusculaires (AMF) soient présents des habitats collinaires aux habitats alpins, les recherches sur leur rôle dans l’écosystème montagnard sont encore incomplètes. Les objectifs de cette thèse sont d’analyser l’écologie et le fonctionnement des AMF ainsi que leur réponse au changement global dans les écosystèmes montagnards. Nous tentons de répondre aux questions de recherche suivantes : quels sont les effets de l’altitude sur les AMF indépendamment des effets des autres gradients et de la relation AMF-plante hôte ? Quelles relations de facilitation se développent dans les écosystèmes montagnards et quels bénéfices les plantes tirent-elles des AMF ?Avec l’augmentation d’un stress environnemental la symbiose AMF-plante doit théoriquement devenir plus mutualiste. Nous émettons l’hypothèse d’une modification du fonctionnement des interactions AMF-plante selon un gradient altitudinal dans les conditions environnementales actuelles, puis dans les conditions futures. Afin de vérifier ces hypothèses, une expérimentation in situ a été mise en place dans les Alpes Centrales d’Italie pour évaluer les variations des taux de mycorhization et leur abondance dans la communauté microbienne du sol, étudier la nature des relations entre plantes et mycorhizes ainsi que la productivité végétale le long d’un gradient altitudinal. De plus, les influences d’une augmentation de la température et d’une réduction des précipitations sont analysées séparément dans une chambre de croissance sous conditions contrôlées, ce qui permet de distinguer leurs effets respectifs sur la productivité des plantes et sur les interactions plantes – mycorhizes.Cette thèse montre que les AMF sont omniprésents dans les écosystèmes de montagne et qu’une diminution de leur abondance avec l'altitude dépend du contexte climatique global. D'autre part, la relation des AMF avec les plantes est fortement dépendante de la plante-hôte, ainsi que du contexte biotique et abiotique. Troisièmement, un changement des interactions AMF-plante avec l'altitude est suggéré par des indices indirects, mais est également très probablement dépendant de l'identité de la plante hôte. Cette thèse propose aussi une nouvelle orientation de recherche pour bien évaluer les hypothèses présentées. Il est nécessaire de réaliser des études sur le terrain où la présence des AMF est contrôlée et les interactions AMF-plante peuvent être évaluées. Afin de généraliser les résultats, ces expérimentations doivent être menées à différentes échelles spatiales et représenter différentes aires géographiques.Il est particulièrement important de comprendre et de qualifier ces processus en zone montagnarde pour prévoir leur évolution possible dans un contexte de changement global. Nos expérimentations montrent en effet que le réchauffement est un facteur important car il aggrave les conditions de sécheresse en basse altitude et entraine une baisse de la productivité des plantes. Nous démontrons que la présence de mycorhizes atténue l’impact du changement climatique sur la productivité des plantes mais que le niveau de cette atténuation varie selon les espèces de plantes.Les connaissances actuelles concernant les AMF en milieu montagnard sont peu développées sur les processus en jeu dans les interactions AMF-plantes. Grâce aux hypothèses présentées et à leur approche expérimentale cette thèse offre de nouvelles perspectives sur l’analyse de ces processus
Even though arbuscular mycorrhizal fungi (AMF) are present from foothills to all alpine habitats, research on their role in mountain ecosystems remains incomplete. The main objective of this dissertation was to investigate interactions between AMF and plants along altitudinal gradients under both, natural conditions and simulated future climate change conditions.A novel framework is suggested for the functioning of the AMF-plant relationship along altitudinal gradients based on the stress gradient hypothesis. The first hypothesis expects the AMF-relationship to shift along the mutualism–parasitism continuum following changing environmental stress along the altitudinal gradient. The relationship might be most mutualistic at the subalpine zone. In a second hypothesis, this shift along the mutualism-parasitism continuum is predicted to be different under climate change conditions, and the most mutualistic expression of the AMF-plant relationship expected in the montane and alpine zone. Studies to validate the presented hypotheses will help to identify important mechanisms underlying plant-AMF interaction and with that the mediation of plant-plant interactions by AMF. In the scope of this thesis, the framework was addressed in field experiment as well as under controlled conditions in a climate chamber experiment.From a literature review and from a field experiment along a dry inner-alpine altitudinal gradient this thesis proposes the following conclusions: First, AMF are also ubiquitous in mountain ecosystems, but a decrease in their abundance with increasing altitude is dependent on the overall climatic context. Second, their relationship to plants is however strongly dependent on the host plant species as well as the biotic and abiotic context. Third, a shift of the AMF-relationship along with altitude is expected but will quite possibly also depend on the plant species identity. Fourth, to fully assess the suggested working hypotheses for AMF-plant interactions field studies must be conducted at different spatial scales and covering different mountain systems.It is particularly important to understand and investigate the drivers of AMF plant relationship in mountain ecosystems to be able to make sound predictions for AMF-plant interactions under future climate change conditions. The presented field and climate chamber experiments on climate change show that temperature is an important factor because it aggravates the conditions of drought in lowland and a threshold is surpassed. It becomes also clear that whether AMF mitigate climate change effects for plants or not is dependent on the plant species. Altogether this thesis contributes to current research questions in ecology, climate change mitigation and plant–soil interactions, because it addresses the role of AMF in mountain grassland ecosystem, investigates the effects of climate change and provides a new framework concerning the functioning of the AMF-plant relationship ranging from parasitism to mutualism

The conversion of native forest to agricultural land has been an on-going issue threatening the health of New Zealand’s freshwater systems. However, despite the fact that this has been occurring since early European settlement, our understanding of the mechanistic relationships between riparian vegetation and stream condition are poorly developed. This research investigated: (i) how forests affect downstream benthic macroinvertebrate communities in pasture and the environmental factors driving community change; (ii) how upstream forest size impacted the rate of change in downstream environmental drivers and associated macroinvertebrate community structure; and (iii) whether the addition of coarse particulate organic matter (a single potential driver of forest community structure) can reset community structure to that of a forested state. Physico-chemical conditions, basal energy resources, and macroinvertebrates were surveyed in several New Zealand headwater streams. At Mount Egmont National Park, 10-12 sites were surveyed across a longitudinal forest-pasture gradient in each of five streams flowing from continuous forest to dairy farmland. My results showed that forests can have marked effects downstream. From the forest edge, water temperatures increased consistently, with a rise of approximately 0.2ºC per 100 m of downstream distance. By contrast, coarse particulate organic matter (CPOM) decreased rapidly downstream of the forest, however, low levels of “forest-derived” CPOM were still present 300m downstream from the forest edge. These environmental changes drove significant shifts in macroinvertebrate community structure. Moreover, pasture communities were markedly different from those in forest, despite being only 100 m from the forest edge. In particular, total macroinvertebrate and EPT richness and densities decreased, and communities shifted from evenly distributed allochthonous-based communities to autochthonous-based communities, highly dominated by molluscs (e.g., Potamopyrgus spp.) Subsequent surveys of 6-8 sites across a longitudinal forest-pasture gradient in each of eleven streams flowing from forest fragments of different sizes into grazed pastures throughout the Canterbury region, indicated that stream temperature increased more rapidly downstream of small- and medium-sized fragments, than larger fragments. A Berger-Parker dominance index also indicated that macroinvertebrates responded principally to water temperature, with communities being more highly dominated by temperature-tolerant molluscs in streams flowing from small-sized forest fragments. Several headwater streams in Canterbury were also highly retentive, with marked CPOM rarely exported beyond 50 m downstream of the forest. Experimental additions of leaf litter to the pasture reaches of the same streams dramatically increased amounts of stored benthic CPOM. Although non-significant, trends indicated that EPT and shredder densities increased at litter addition sites, providing promise that CPOM can function as a mechanism directly enhancing healthy stream communities. My findings support the contention that when the replanting of entire stream reaches is infeasible, the use of riparian management strategies which focus on the planting of intermittent patches along stream banks can potentially improve stream habitat and community health downstream.

There is a desire to source novel legume species to combat the threat of dryland salinity to agriculture and the environment. There are already many legume weeds in temperate Australia and the potential negative impact of new species has created a justifiable impasse. Weed risk assessment presents a potential solution, but deficiencies in the current Australian system have hampered progress thus far. A greater emphasis on the impact of the weed species may be a means of solving this conflict. Therefore, this project attempted to predict the level of impact that a legume species would have upon temperate natural ecosystems. The weed impact of exotic legume species in natural ecosystems was determined by distributing a questionnaire to experts. Respondents reported that woody perennial legumes were more important than herbaceous legumes. Field measurements demonstrated that the abundance of legumes was correlated with their perceived impact in natural ecosystems. Thus, two test species lists were compiled, one of woody species and the other herbs. The woody species comprised three impact levels: major, moderate and no impact. The herbaceous species also comprised three lower impact levels: consequential, inconsequential and no impact. The identification of legume species with differing levels of impact subsequently allowed them to be compared with respect to a number of biological traits, with the aim of distinguishing impact groups based on these traits. Seedling growth was examined in the glasshouse under both high and low soil moisture. With high soil moisture, major and moderate impact legumes were distinguished by having a higher specific root length than no impact legumes. Consequential impact herbaceous legumes had lower specific leaf area than the lower impact groups. Moisture stress did not alter the comparisons between impact groups. Five reproductive traits were explored through a mixture of experimental, field sampling and literature research. Major and moderate impact legumes had a shorter juvenile period, higher seed dormancy, a smaller seed mass and higher seed production than no impact legumes. Major and moderate impact legumes could be differentiated by their seed mass and seed production. Consequential and inconsequential impact herbaceous species had higher seed production and seed dormancy than no impact species. To allow for important interactions with the environment, the ability of the test legumes to establish in temperate natural ecosystems with and without physical disturbance was studied. This provided some test of the conclusions reached from individual trait studies. The highest impact legumes were the most successful at establishing in the natural ecosystems studied. Disturbance had a positive effect on establishment, except for the major impact group where disturbance was not important. This study was able to highlight that for a legume to successfully naturalise in temperate Australia it must possess certain biological traits. Less success was achieved in distinguishing naturalised legumes of differing impact. However, growth form is important and seed mass appears a significant trait in regard to woody species. Both are easily measured traits and could be incorporated in weed risk assessment of legumes in the future.
http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1284153
Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine 2007

There is a desire to source novel legume species to combat the threat of dryland salinity to agriculture and the environment. There are already many legume weeds in temperate Australia and the potential negative impact of new species has created a justifiable impasse. Weed risk assessment presents a potential solution, but deficiencies in the current Australian system have hampered progress thus far. A greater emphasis on the impact of the weed species may be a means of solving this conflict. Therefore, this project attempted to predict the level of impact that a legume species would have upon temperate natural ecosystems. The weed impact of exotic legume species in natural ecosystems was determined by distributing a questionnaire to experts. Respondents reported that woody perennial legumes were more important than herbaceous legumes. Field measurements demonstrated that the abundance of legumes was correlated with their perceived impact in natural ecosystems. Thus, two test species lists were compiled, one of woody species and the other herbs. The woody species comprised three impact levels: major, moderate and no impact. The herbaceous species also comprised three lower impact levels: consequential, inconsequential and no impact. The identification of legume species with differing levels of impact subsequently allowed them to be compared with respect to a number of biological traits, with the aim of distinguishing impact groups based on these traits. Seedling growth was examined in the glasshouse under both high and low soil moisture. With high soil moisture, major and moderate impact legumes were distinguished by having a higher specific root length than no impact legumes. Consequential impact herbaceous legumes had lower specific leaf area than the lower impact groups. Moisture stress did not alter the comparisons between impact groups. Five reproductive traits were explored through a mixture of experimental, field sampling and literature research. Major and moderate impact legumes had a shorter juvenile period, higher seed dormancy, a smaller seed mass and higher seed production than no impact legumes. Major and moderate impact legumes could be differentiated by their seed mass and seed production. Consequential and inconsequential impact herbaceous species had higher seed production and seed dormancy than no impact species. To allow for important interactions with the environment, the ability of the test legumes to establish in temperate natural ecosystems with and without physical disturbance was studied. This provided some test of the conclusions reached from individual trait studies. The highest impact legumes were the most successful at establishing in the natural ecosystems studied. Disturbance had a positive effect on establishment, except for the major impact group where disturbance was not important. This study was able to highlight that for a legume to successfully naturalise in temperate Australia it must possess certain biological traits. Less success was achieved in distinguishing naturalised legumes of differing impact. However, growth form is important and seed mass appears a significant trait in regard to woody species. Both are easily measured traits and could be incorporated in weed risk assessment of legumes in the future.
Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine 2007

This thesis examines the hypothesis that, in southern New South Wales and northeast Victoria, Australia, palatable taxa of E. curvula offer advantages that complement those of the species that are traditionally sown in temperate pastures in a landscape context.This hypothesis was based on a review of literature showing that, prior to European settlement, the vegetation, the landscape and the climate were broadly in balance, and the wateruse pattern of the vegetation of southeastern Australia resulted in water being used more-or-less completely by the end of summer. This maximised the capacity of the soil to take up and store water during autumn and winter.Three grazing experiments and one spaced-plant species evaluation study were used to assess the role of summer-growing, C4 Eragrostis curvula in pastures in the temperate zone of southeastern Australia.Issues relating to pasture production and the productivity of wool-growing sheep were investigated. Factors affecting the sustainability of the pastures and their potential on and off site impacts were emphasised.Modelling was used to explore issues of water use, arising from the grazing experiments. It is concluded that the persistence, production, water use patterns, and the adaptability of palatable varieties of E. curvula make it a useful and complementary addition to the range of species that are currently available for use as sown pastures in southern Australia.

Three studies were undertaken from 2006 to 2007 to examine litter (dead plant material) in southwestern Manitoba pastures. First, the relationship between litter and soil microclimate was tested across five pasture sites. The amount of litter biomass was not strongly related to soil moisture, though near-surface soil temperatures were reduced when litter was present. Second, the effect of four simulated grazing strategies on the litter layer was measured in six pastures. It was found that after three years of simulated grazing, litter was present in largest quantities in the least-frequently grazed treatments. Finally, a field survey was conducted assessing the quantity of litter present in native pastures across Manitoba. Litter was quite variable and averaged 1902 kg/ha over two years. This research confirmed the value of litter as an indicator of sustainable pasture management, though it remains unclear whether litter is important to pastures from the perspective of soil microclimate.
October 2008

Global surface temperatures have been rising since the pre-industrial era and are predicted to continue rising due to the positive radiative forcing of greenhouse gases in the atmosphere. The atmospheric concentration of carbon dioxide (CO\(_2\)), the gas responsible for most of this warming, has increased since the industrial revolution due to the burning of fossil fuels and land use change. The concentration of nitrous oxide (N\(_2\)O), a potent greenhouse gas with substantially higher global warming potential than CO\(_2\) over a 100-y horizon, has similarly increased due to agriculture and nitrogenous fertiliser use. In addition to warming the earth’s surface, elevated CO\(_2\) (eCO\(_2\)) may change terrestrial carbon (C) and nitrogen (N) cycling due to plant responses to increased C availability. Plants respond to eCO\(_2\) in two ways: through increased biomass production and increased water-use efficiency. These responses may alter the availability of C, N and water in soils, which could affect microbial activity through shifts in substrate availability and soil aerobic status. As many processes mediated by microbes release CO\(_2\) and N\(_2\)O, it is likely that both plant responses to eCO\(_2\) could alter these gas fluxes. Soils are the largest source of CO\(_2\) and N\(_2\)O, making it essential that accurate predictions of future greenhouse gas emissions include the response of these processes to eCO\(_2\). Using a temperate pasture dominated by Lolium perenne, this study measured the impact of three levels of CO\(_2\) concentration (400, 475 and 550 μmol CO\(_2\) mol\(^{-1}\)) on the emission of CO\(_2\) and N\(_2\)O. Additionally, water supply was independently controlled via irrigation treatments (adequate, excess = +20% and limit = -40%) to determine if CO\(_2\)-effects on soil processes were driven by plant production, soil water content or both. Plant biomass was increased under 550 μmol CO\(_2\) mol\(^{-1}\) relative to ambient due entirely to greater root growth but no similar change in production was present under 475 μmol CO\(_2\) mol\(^{-1}\). Plant N requirements were increased under eCO\(_2\) relative to ambient, resulting in additional N immobilised in plantbiomass under eCO\(_2\) and substantially lower soil mineral N availability. Consequently, N\(_2\)O emissions were never higher under eCO\(_2\) than ambient and were often lower. This effect dramatically reduced N\(_2\)O emissions from this pasture with the strongest effect in the week following fertiliser application when emissions were highest. Under eCO\(_2\), soil CO\(_2\) emissions were higher than at 400 μmol CO\(_2\) mol\(^{-1}\), though mean emissions were similar between 475 and 550 μmol CO\(_2\) mol\(^{-1}\). Similarly, the rate of root decomposition in soils under eCO\(_2\) was higher than in control plots as was the loss of soil C. The CO\(_2\)-effect on both CO\(_2\) and N\(_2\)O emissions was independent of soil water content, demonstrating that the CO\(_2\)-effect on plant production and organic matter inputs drove the processes underlying these fluxes. Therefore, eCO\(_2\) had a strong effect on the emission of CO\(_2\) and N\(_2\)O from this temperate pasture. In particular, N\(_2\)O emissions were suppressed by the CO\(_2\)-effect on plant N immobilisation and CO\(_2\) emissions were accelerated due to increased belowground C input. Importantly, the effects of soil water content on these emissions were absent in this system entirely, suggesting that the CO\(_2\)-effect on plant production can have a substantial impact on greenhouse gas emissions from temperate pastures.

Climate change-induced increases in global air temperature and concurrent modulations in the hydrological cycle have led to higher levels of drought stress globally. Grassland ecosystems such as pastures are particularly sensitive to climate change as they lack the deep roots and carbohydrate reserves that partially dampen the negative impact of abiotic stress in woody plant systems. Pastures have significant economic and ecological value, and it is important to assess the current and future impact of climate change on these systems. While many studies have investigated the response of pasture species to warming and drought separately, few studies have focused on their interactions. Furthermore, the mechanistic basis for the response of pasture species to abiotic stress, especially drought and heat stress, is not well understood. While the mechanisms underlying drought-induced impacts on hydraulic processes are well studied in woody species, there are currently few assessments in pasture grasses. In this thesis, I examined leaf gas exchange and hydraulic traits across a range of widely cultivated pasture species from different plant functional groups and investigated the response of these traits to warming and drought stress. My research sought to understand how these traits determine plant function under normal and abiotic stress conditions and how that will determine the response of pasture systems in a warmer, drier future. The primary objective was to identify more resilient pasture species and investigate the mechanistic basis for their resilience, aiding the development of species selection and management strategies that may mitigate the effects of climatic change. Findings show that increases in global air temperature may not have a positive impact on the productivity of pasture species in eastern Australia, even during the cool season and warming will have a more negative impact on C3 pasture species than C4 species during warmer periods. We found that the ability to resist xylem embolism and hydraulic dysfunction, rather than recovery, underpins pasture species resilience to drought, with early stomatal closure being crucial to species’ survival under water limiting conditions. Collectively, climate change induced increases in air temperature and drought are likely to have negative impacts on growth and productivity of temperate C3 pasture species and physiological adjustment may not be sufficient to alleviate the impacts of rapid global change. Therefore, an overall decline in temperate C3 species performance and an increase in C4 dominance are expected in pastures in a warmer, drier future.