Academic literature on the topic 'Cation ratio of soil structural stability (CROSS)'

Sodium salts tend to dominate salt-affected soils and groundwater in Australia; therefore, sodium adsorption ratio (SAR) is used to parameterise soil sodicity and the effects of sodium on soil structure. However, some natural soils in Australia, and others irrigated with recycled water, have elevated concentrations of potassium and/or magnesium. Therefore, there is a need to derive and define a new ratio including these cations in place of SAR, which will indicate the dispersive effects of Na and K on clay dispersion, and Ca and Mg on flocculation. Based on the differential dispersive effects Na and K and the differential flocculation powers of Ca and Mg, we propose the concept of ‘cation ratio of soil structural stability’ (CROSS), analogous to SAR. This paper also gives the results of a preliminary experiment conducted on three soils varying in soil texture on hydraulic conductivity using percolating waters containing different proportions of the cations Ca, Mg, K, and Na. The relative changes in hydraulic conductivity of these soils, compared with the control treatment using CaCl2 solution, was highly correlated with CROSS. Clay dispersion in 29 soils treated with irrigation waters of varying cationic composition was highly correlated with CROSS rather than SAR. It was also found that CROSS measured in 1 : 5 soil/water extracts was strongly related to the ratio of exchangeable cations. These results encourage further study to investigate the use of CROSS as an index of soil structural stability in soils with different electrolytes, organic matter, mineralogy, and pH.

Non-destructive X-ray computed tomography (µCT) scanning was used to characterise changes in pore architecture as influenced by the proportion of cations (Na, K, Mg, or Ca) bonded to soil particles. These observed changes were correlated with measured saturated hydraulic conductivity, clay dispersion, and zeta potential, as well as cation ratio of structural stability (CROSS) and exchangeable cation ratio. Pore architectural parameters such as total porosity, closed porosity, and pore connectivity, as characterised from µCT scans, were influenced by the valence of the cation and the extent it dominated in the soil. Soils with a dominance of Ca or Mg exhibited a well-developed pore structure and pore interconnectedness, whereas in soil dominated by Na or K there were a large number of isolated pore clusters surrounded by solid matrix where the pores were filled with dispersed clay particles. Saturated hydraulic conductivities of cationic soils dominated by a single cation were dependent on the observed pore structural parameters, and were significantly correlated with active porosity (R2 = 0.76) and pore connectivity (R2 = 0.97). Hydraulic conductivity of cation-treated soils decreased in the order Ca > Mg > K > Na, while clay dispersion, as measured by turbidity and the negative charge of the dispersed clays from these soils, measured as zeta potential, decreased in the order Na > K > Mg > Ca. The results of the study confirm that structural changes during soil–water interaction depend on the ionicity of clay–cation bonding. All of the structural parameters studied were highly correlated with the ionicity indices of dominant cations. The degree of ionicity of an individual cation also explains the different effects caused by cations within a monovalent or divalent category. While sodium adsorption ratio as a measure of soil structural stability is only applicable to sodium-dominant soils, CROSS derived from the ionicity of clay–cation bonds is better suited to soils containing multiple cations in various proportions.

We have used the newly developed concept of CROSS (cation ratio of soil structural stability) instead of SAR (sodium adsorption ratio) in our study on dispersive soils. CROSS incorporates the differential dispersive powers of Na and K and the differences in the flocculating effects of Ca and Mg. The CROSS of the dispersed soil solutions, from the differently treated soils of three soil types varying in clay content, mineralogy, and organic matter, was highly correlated with the amount of clay dispersed. The relation between CROSS and exchangeable cation ratio depended on soil type, and particularly organic matter and the content and mineralogy of clay. Threshold electrolyte concentration of the flocculated suspensions was significantly correlated with CROSS of the dispersed suspensions. The cationic flocculating charge of the flocculated suspensions, which incorporates the individual flocculating powers of the cations, was significantly correlated with CROSS. However, these types of relations will depend on several soil factors even within a given soil class. Therefore, we have derived the dispersive potential of an individual soil from which we calculated the required cationic amendments to maintain flocculated soils and their structural integrity.

Effects of soil solution cation concentrations and ratios on hydraulic properties must be understood in order to model soil water flow in reactive soils or develop guidelines for sustainable land application of wastewater. We examined effects of different ratios and concentrations of the cations Ca2+, Mg2+, Na+, and K+, using hydraulic conductivity measurements in repacked soil cores, as an indicator of soil structural stability. We examined widely used indices—sodium, potassium, and monovalent cation absorption ratios (SAR, PAR, MCAR)—which assume that the flocculating effects of Ca2+ and Mg2+ are the same, and the dispersive effects of Na+ and K+ are the same. Our laboratory measurements indicate that at any given values of MCAR, the reductions in soil hydraulic conductivity with decrease in electrolyte concentration are not identical for different cation combinations in solution. The hydraulic conductivity curves showed a marked lateral shifting for both the surface and subsurface soils from a winery wastewater application site. This indicates that MCAR is inadequate as a soil stability parameter in soil solutions containing a mixture of Na+, K+, Ca2+, and Mg2+. We employed an unpublished equation that was proposed by P. Rengasamy as a modified index of soil stability for mixed cation combinations, using calculated relative flocculating powers of different cations (‘CROSS’, cation ratio of structural stability). Our observation of lateral shift in hydraulic conductivity measurements at any value of MCAR appears to relate to changes in CROSS values for all cation combinations tested, except for K–Mg solutions, for which a more generalised CROSS equation with modified parameters seems more suitable for calculating the CROSS value. Appropriate modified parameters for use in this generalised CROSS equation were determined empirically, using the experimental data. We derived a combination of threshold electrolyte concentration and CROSS values required to maintain high hydraulic conductivity for the soils at a winery wastewater application site. The potential use of this relationship in developing management practices for sustainable wastewater management at the site is discussed. Further research on the applicability of CROSS and generalised CROSS equations for other soils in the presence of different mixed cation combinations is needed.

The high proportion of adsorbed monovalent cations in soils in relation to divalent cations affects soil structural stability in salt-affected soils. Cationic effects on soil structure depend on the ionic strength of the soil solution. The relationships between CROSS (cation ratio of soil structural stability) and the threshold electrolyte concentration (TEC) required for the prevention of soil structural problems vary widely for individual soils even within a soil class, usually attributed to variations in clay mineralogy, organic matter, and pH. The objective of the present study was to test the hypothesis that clay dispersion influenced by CROSS values depends on the unique association of soil components, including clay and organic matter, in each soil affecting the net charge available for clay–water interactions. Experiments using four soils differing in clay mineralogy and organic carbon showed that clay dispersion at comparable CROSS values depended on the net charge (measured as negative zeta potential) of dispersed clays rather than the charge attributed to the clay mineralogy and/or organic matter. The effect of pH on clay dispersion was also dependent on its influence on the net charge. Treating the soils with NaOH dissolved the organic carbon and increased the pH, thereby increasing the negative zeta potential and, hence, clay dispersion. Treatment with calgon (sodium hexametaphosphate) did not dissolve organic carbon significantly or increase the pH. However, the attachment of hexametaphosphate with six charges on each molecule greatly increased the negative zeta potential and clay dispersion. A high correlation (R2 = 0.72) was obtained between the relative clay content and relative zeta potential of all soils with different treatments, confirming the hypothesis that clay dispersion due to adsorbed cations depends on the net charge available for clay–water interactions. The distinctive way in which clay minerals and organic matter are associated and the changes in soil chemistry affecting the net charge cause the CROSS–TEC relationship to be unique for each soil.

Treated wastewater (TWW) is considered as an alternative for agricultural irrigation. The aim of this study was to understand the medium- and long-term effects of TWW on soil physicochemical parameters. Two perimeters (P1 and P2)receiving TWW for 38 and 20 years, respectively, in Tunisiawere selected for study. In each perimeter, two water types were adopted: TWW and groundwater (GW). Soil physicochemical traits (pH, EC, and concentrations of Na+, K+, Ca2+, and Mg2+) were measured up to 100 cm, and three indexes were calculated: sodium adsorption ratio (SAR), cation ratio of structural stability (CROSS), and cation exchange capacity (CEC). Overall, all soil parameters were significantly affected in the irrigation area using GW. However, in the case of TWW, only the pH was found to be affected, increasing by 4.7% from P1 to P2. Moreover, compared to GW, TWW enhanced the soil salinity by 127%, particularly at deeper subsoils. More interestingly, the results revealed an accumulation of Mg2+, Ca2+, and K+ and a depletion of Na+ at the soil surface. Notably, TWW showed the lowest CROSS and SAR indexes, indicating the benefits of applying TWW even after long-term use in improving soil physicochemical parameters such as sodicity and structural stability. Our results provide valuable information for decision-makers to use wastewater in irrigated marginal soils.

The biochar application can improve the physiochemical properties of both sandy and clayey loam soils and is considered a potential adaptation tool toward climate change. Therefore, the current study is novel in combining water-hyacinth-derived biochar with organic manures as a suggested effective way of treating the soil with biochar under arid and semiarid conditions. Water hyacinth weeds were slow pyrolyzed at a temperature of 300 °C, which resulted in nonalkaline biochar with a pH value of 6.31, which is suitable for alkaline soils. A pot experiment was established to study the impact of the solo application of nonalkaline water-hyacinth-derived biochar (WHB) and its combined application with farmyard (WHB/FM) and poultry manure (WHB/PM) at a rate of 1.5 and 3%, respectively, on some chemical and physical properties of sandy and clay loam soils and some barley’s growth parameters. WHB, WHB/FM, and WHB/PM significantly affected the soil pH at different application rates (1.5 and 3%) in sandy soil. A considerable alteration in water-stable aggregates (WSA), dispersion ratio (DR), available water content (AWC), and cation ratio of soil structural stability (CROSS) index resulted from combining manures (FM and PM) with biochar better than the solo application of biochar. WHB/PM treatments had a superior effect in improving barley’s growth. Relative increases were by 37.3 and 11.0% in plant height and by 61.6 and 28.5% in the dry matter in sandy and clayey loam soils, respectively. Under the conditions of this study, we can conclude that treating the soil with WHB/PM at a rate of 1.5 and 3% is the most effective application. The current study may have a vital role in Egyptian agriculture sustainability by enhancing the soil characteristics of the old agricultural and the newly reclaimed lands.

Water is a prime natural resource and precious national asset and one of the chief constituents of the environment. The chemical characteristics play a key role in terms of ecological and economic perspectives in the river water. The characterization and evaluation of river water quality in the Karmanasha River is necessary due to its immense importance in the livelihood of the people in the core urban areas of Kathmandu valley, Nepal. In this study, the surface water samples were collected from 16 sites with a 0.5 km interval to characterize and evaluate the water quality mainly from the perspective of its irrigational usage. The assessment was carried out by applying electrical conductivity (EC), sodium percentage (Na%), sodium adsorption ratio (SAR), permeability index (PI), Kelly’s ratio (KR), magnesium adsorption ratio (MAR), cation ratio of soil structural stability (CROSS), Wilcox diagram and water quality index (WQI) including the general hydrochemistry. The general hydrochemistry of river water indicates slightly alkaline in nature with mean pH value 8.07, and the dominance order of major ions follows the pattern of Ca2+>Mg2+>Na+>K+ for cations, and HCO3->Cl->NO3- for anions. Furthermore, the results revealed that the water is safe for irrigation purposes based on EC, Na%, SAR, KR, MAR, CROSS, and Wilcox diagram. The results also specified that no severe degradation in water, however, the low DO, and high BOD and COD values than that of the standard value prescribed by Nepal Drinking Water Quality Standard, signify the anthropogenic signature in the river water. This study provides the baseline information about the WQI and suitability of irrigation water quality, and further in-depth studies are required at spatiotemporal levels to get in-depth insights about the ecological health of the river.

AbstractIn this study, we investigated the impact of adding solutions with different potassium and sodium concentrations on dispersible clay, water retention characteristics, air permeability, and soil shrinkage behaviour using two agricultural soils from Switzerland with different clay content but similar organic carbon to clay ratio. Three different solutions (including only Na, only K, and the combination of both) were added to soil samples at three different cation ratio of soil structural stability levels, and the soil samples were incubated for one month. Our findings showed that the amount of readily dispersible clay increased with increasing Na concentrations and with increasing cation ratio of soil structural stability. The treatment with the maximum Na concentration resulted in the highest water retention and in the lowest shrinkage capacity. This was was associated with high amounts of readily dispersible clay. Air permeability generally increased during incubation due to moderate wetting and drying cycles, but the increase was negatively correlated with readily dispersible clay. Readily dispersible clay decreased with increasing K, while readily dispersible clay increased with increasing K in Iranian soil (Part I of our study). This can be attributed to the different clay mineralogy of the studied soils (muscovite in Part I and illite in Part II).

About 35% of the total land area in Australia is affected by different categories of salt-affected soils. Apart from natural salinity, a significant proportion of the cultivated land has become saline due to irrigation, particularly where groundwater or recycled waters were used. Sodium salts tend to dominate salt affected soils and groundwater in Australia, therefore sodium adsorption ratio (SAR) and exchangeable sodium percentage (ESP) are currently used to assess the effects of sodium on soil structure. However, the literature review has identified that the solutions of salt–affected and fresh water or wastewater irrigated soils may contain elevated concentrations of potassium and/or magnesium, which may affect the levels of soluble and exchangeable cations, and lead to soil structural deterioration due to clay dispersion and swelling. Traditional indices SAR and ESP, used for assessing soil structure, do not take into account the effects of K on soil clay dispersion and swelling. Furthermore, although exchangeable Mg has not been included within the common definition of sodicity, there has been disagreement concerning its influence on the behaviour of sodic soils. In addition, in the SAR model Ca²⁺ is equated to Mg²⁺ in flocculating power. Consequently the use of SAR and ESP, as the indices of soil structural stability, can be misleading when soil structure is negatively affected by the high amount of monovalent K⁺, and the concentration of Mg in soil solution and exchange sites is higher than that of Ca. In the research reported in this thesis, a newly developed concept of CROSS (cation ratio of soil structural stability) has been used, instead of SAR, as an index for assessing soil structural changes affected by different cations in soils. Traditional index SAR is defined as SAR = Na / √(Ca+Mg)/2 & New index, CROSS is defined as : CROSS = Na+0.56K / √(Ca+0.6Mg)/2 where the concentrations of these ions (Na, K, Ca and Mg) are expressed in milli moles of charge/L. While SAR as a measure of soil structural stability is only applicable to sodium dominant soils, CROSS derived from the ionicity of clay-cation bond is better suited to soils containing multiple cations in various proportions. In contrast to SAR, the differential effects of Na and K in dispersing soil clays and the differential effects of Mg and Ca in flocculating soil clays are considered in the CROSS model. The main objectives of this thesis were to investigate the effects of elevated concentration of K and Mg on soil structure in combination with the other cations, and to assess the applicability of CROSS as an index of structural stability for salt-affected soils by using soils of different clay mineralogy, texture, electrolyte concentration, pH and organic matter. Further, to identify potential ways to manage structural stability of these soils and to improve their physical condition. Studies on pure clay systems have been included to understand the fundamental processes involved in dispersion in soil clays. The primary outcomes of this research were a series of peer reviewed scientific papers, which centred on the following key findings: 1. The deleterious effects of increasing concentration of K on clay dispersion and hydraulic conductivity were confirmed for three soil types of different clay mineralogy, pH EC and organic matter. Non- destructive X-ray CT scanning provided a means of measuring changes in soil porosity and pore connectivity. 2. The ionicity indices of the cations Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺ were theoretically derived using their ionisation potentials and charge. The behaviour of two pure clays (illite and bentonite) and two soil clays in aqueous suspension was investigated. As the ionicity index decreased in the following order Li⁺ > Na⁺ > K⁺ > Mg²⁺ >Ca²⁺ > Sr²⁺ > Ba²⁺ the tendency to covalency increased and, hence, the predisposition to break the clay-cation bonds in water decreased. Strong and significant relationships between ionicity indices of cations in clay–cation bonds and clay behaviour such as dispersivity (r²=0.93) and zeta potential (r²=0.84) confirm that the degree of ionicity in these bonds dictates the water interaction with clay particles, leading to their separation from the clay aggregates. The strong relationships between zeta potential and the degree of dispersivity (r²=0.78) suggests that surface charge on clays is responsible for the variations in correlations between ionicity indices and clay behaviour among the four types of clays. 3. Effects of clay-cation bonding on soil structure were further validated by non destructive X-ray computed tomography (μCT) scanning of the cation treated soil samples. Changes in pore architecture as influenced by the proportion of cations (Na⁺, K⁺, Mg²⁺ and Ca²⁺) bonded to soil particles were characterised. All the structural parameters, studied by μCT scanning, were highly correlated with the ionicity indices of dominant cations, confirming that the structural changes during soil-water interaction depend on the ionicity of clay cation bonding. Saturated hydraulic conductivity of cation treated soils dominated by a single cation were dependant on the observed structural parameters, and were significantly correlated with active porosity (r²=0.76) and pore connectivity (r²=0.97) characterised by μCT scan. 4. Applicability of CROSS as a new index of soil structural stability was methodically validated and confirmed in series of studies for a range of soils containing varying quantities of Na, K, Mg, and Ca. The effects of CROSS were highly dependent on the total electrolyte, soil texture, clay mineralogy, pH and organic matter content. 5. Useful threshold values of the electrolyte concentration required to flocculate the dispersed suspension were derived. Threshold electrolyte concentration (TEC) of the flocculated suspensions of three soils were significantly correlated with CROSS of the dispersed suspensions (r²=0.93). Again, when the individual soil type was considered, smectitic clay with high negative charge had lower TEC than the illitic or kaolinitic clay. The cationic flocculating charge of the flocculated suspensions (CFC), which incorporate the individual flocculating power of the cations, was significantly correlated with CROSS. However, these types of relationships will depend on several factors even within the given soil class. Therefore, the dispersive potential (Pdis) of the individual soil was derived, from which the required amount of the cationic amendments can be calculated to maintain flocculated soils and their structural integrity. 6. The research results presented within this thesis clearly demonstrate that clay dispersion influenced by CROSS values depends on the unique association of soil components affecting the net charge (measured as negative zeta potential) available for clay-water interaction, rather than the charge attributed to the clay mineralogy and/or organic matter. Soil with smectitic mineralogy and high cation exchange capacity dispersed less than soils dominant in illitic and kaolinitic clays. In successive experiments, soils differing in clay mineralogy, organic carbon and pH were treated with solutions of varying CROSS, NaOH and sodium hexa- meta phosphate (calgon) respectively. Where the high organic carbon of the soil was bonding with clay surface, the charge was reduced considerably. Treating this soil with NaOH led to the dissolution of organic carbon and increased the pH, thereby increasing the net charge and clay dispersion. The treatment with calgon did not dissolve the organic carbon or increase the pH. Nevertheless, the attachment of hexa-meta phosphate with six negative charges on each molecule greatly increased the negative zeta potential and clay dispersion. A high correlation (r²=72) was obtained between the dispersed clay content and zeta potential of all soils with different treatments confirming that the net charge on the soil surface available for water interaction controls the dispersion-flocculation phenomena. The research outcomes presented in this thesis have significantly contributed to theoretical and practical knowledge concerning the effects of cations in soils and irrigation waters on soil structure. The new structural stability index, CROSS, validated in this thesis, provides a far more comprehensive assessment of the structural stability of soils affected by salinity, naturally or due to different quality of irrigation waters, than the traditionally used indices such as sodium adsorption ration (SAR), monovalent cation ratio (MCAR) or potassium adsorption ratio (PAR). Furthermore, CROSS provides an accurate and more suitable guideline for the use of irrigation water of different cation composition (e.g. recycled water), which enables management decisions on the suitability and the rate of irrigation water. The dispersive potential for individual soils, derived in this research, will facilitate calculation of the required cationic amendments to maintain flocculated soils and their structural integrity.
Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2013