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The demand for the use of marginal‐quality water as an irrigation resource is increasing in arid and semiarid region lands due to the freshwater shortage. Marginal waters usually have high salinity and high alkalinity and may contain high proportions of ions such as sodium. This study investigated the impact of irrigation water pH on saturated hydraulic conductivity (Ks), cation exchange capacity, net particle charge, and dispersivity of soils. Nine soils with differing pH, alkalinity, clay content, and mineralogy were used in leaching column experiments, with solutions of varying sodium adsorption ratio (20 and 40), electrical conductivity (0.8, 1.5, 2.5, 5, 10, 25, and 50 dS m−1), and pH (6, 7, 8, and 9). The desired pH was achieved by adjusting the HCO3−/Cl− ratio and CO2 partial pressure using CO2 gas with 99.9% purity. Results showed that the increase of solution pH causes an increase in net negative charges on clay particles, resulting in higher exchangeable cations, negative ζ‐potential, and clay dispersion and movement of dislodged particles into pore spaces, resulting in Ks reduction. This effect was more evident for acidic and low‐clay‐content soils. The Ks reduction in relation to pH was less for smectitic and high clay content soil than for kaolinite dominant soils for all concentrations, suggesting resiliency of the smectitic soils under irrigation water with high pH. Results reinforce that it is essential to consider the original pH, clay content, and mineral of the soil and the pH, electrical conductivity, and sodium adsorption ratio of the irrigation water to accurately predict the Ks reduction of the soil.

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Dispersive spoil/soil management is a major environmental and economic challenge for active coal mines as well as sustainable mine closure across the globe. To explore and design a framework for managing dispersive spoil, considering the complexities as well as data availability, this paper has developed a Bayesian Belief Network (BBN)-a probabilistic predictive framework to support practical and cost-effective decisions for the management of dispersive spoil. This approach enabled incorporation of expert knowledge where data were insufficient for modelling purposes. The performance of the model was validated using field data from actively managed mine sites and found to be consistent in the prediction of soil erosion and ground cover. Agreement between predicted soil erosion probability and field observations was greater than 74%, and greater than 70% for ground cover protection. The model performance was further noticeably improved by calibration of Conditional Probability Tables (CPTs). This demonstrates the value of the BBN modelling approach, whereby the use of currently best-available data can provide a practical result, with the capacity for significant model improvement over time as more (targeted) data come to hand.

The concentration of cationic monomeric aluminium (A13+) was determined in streams draining areas in different land use. Relationships between the concentrations of A13+ and companion ions were examined both for streams and for eluates from soil leached in the laboratory with simulated rainwater that ranged in pH and salt concentration.The concentrations of Ali+ were consistently greater in streams draining Sitka spruce woodland than in streams in adjacent catchments draining rough grazing. In no case was the A13+ concentration governed by the solubility product of gibbsite. The concentrations of A13+ were very closely correlated with excess anions (total inorganic anions minus basic cations) both for stream water and for eluates from soil leached with simulated rainwater at a constant pH equal to that of the soil (3.8).Exchangeable A1 was the source of A13+ in leachates from soil in the laboratory and the displacement of exchangeable Al was the dominant process accounting for the levels of A13+ in acidic streams. Hydrogen ions were much more important than basic cations in displacing exchangeable Al from the acidic soil used in the laboratory experiments and probably from soils in the field. The greater excess of inorganic anions in streams from Sitka spruce woodland probably resulted from a greater anion excess in the input water (acid rain) together with a greater NO, production in the soil. All three major anions, CI, SO, and NO, contributed to the greater anion excess.

Soil‐specific pedotransfer functions can be incorporated into the HYDRUS model. Electrolyte concentration reduces the adverse effect of pH and Na on soil structural stability. Clay content is important in governing soil hydraulic reduction dynamics due to pH. Hydraulic conductivity is a key soil property governing agricultural production and is thus an important parameter in hydrologic modeling. The pH scaling factor for saturated hydraulic conductivity (Ks) reduction in the HYDRUS model was reviewed and evaluated for its ability to simulate Ks reduction. A limitation of the model is the generalization of Ks reduction at various levels of electrolyte concentration for different soil types, i.e., it is not soil specific. In this study, a new generalized linear regression model was developed to estimate Ks reduction for a larger set of Australian soils compared with three American soils. A nonlinear pedotransfer function was also produced, using the Levenberg–Marquardt optimization algorithm, by considering the pH and electrolyte concentration of the applied solution as well as the soil clay content. This approach improved the estimation of the pH scaling factor relating to Ks reduction for individual soils. The functions were based on Ks reduction in nine contrasting Australian soils using two sets of treatment solutions with Na adsorption ratios of 20 and 40; total electrolyte concentrations of 8, 15, 25, 50, 100, 250, and 500 mmolc L−1; and pH values of 6, 7, 8, and 9. A comparison of the experimental data and model outputs indicates that the models performed objectively well and successfully described the Ks reduction due to the pH. Further, a nonlinear function provided greater accuracy than the generalized function for the individual soils of Australia and California. This indicates that the nonlinear model provides an improved estimation of the pH scaling factor for Ks reduction in specific soils in the HYDRUS model and should therefore be considered in future HYDRUS developments and applications.

Land amendment irrigation was effective at reducing structural decline under rapid dilution. Threshold electrolyte concentration analysis and initial Ksat are crucial management factors. High‐frequency rainfall events may cause concern for marginal quality water use in irrigation. Land amendment irrigation (LAI) has become an increasingly useful practice in addressing sodic and alkaline coal seam methane gas (CSG) water for irrigation purposes. However, there is a paucity of information pertaining to rapid dilution of soil solution under LAI management. This study investigated the ability of land amendment to buffer soils against structure degradation under sequential irrigation with CSG water (electrical conductivity [EC], 3 dS cm–1; sodium adsorption ratio [SAR], 100 mmolc L–1; pH 8.4) and rainwater in a highly smectitic black Vertisol (BV) and kaolinitic Oxisol (OX) soil. Stoichiometric quantities of gypsum and sulfur amendments were applied for the LAI process to reduce sodicity and alkalinity to a target of SAR ≤20 and HCO3− alkalinity ≤100 mg L–1. Soils were irrigated with 10 ML ha–1 CSG water and 9 ML ha–1 rainwater in the sequence of 1 ML ha–1 and 0.9 ML ha–1 CSG water and rainwater events, respectively, using a 7.5 mm h–1 rainfall intensity. Saturated hydraulic conductivity was determined and reported as a reduction from initial conductivity. The collected leachates were used for subsequent measurements of pH, EC, SAR, and alkalinity at each event. Results suggested that LAI was inadequate to protect soil structure from more than three of the intensity–frequency–duration events but sufficient for up to three events. This was considered positive evidence for LAI given the annual recurrence of such an event was one for the region. Additional gypsum application had no significant effect on protecting soil from further hydraulic reduction compared with LAI alone. The OX and BV behaved differently in terms of the observed hydraulic reduction, which was determined to be both a function of iron oxides (OX) and the effect of dilution, in contrast to the threshold electrolyte concentration. This highlighted that both the initial hydraulic conductivity and threshold electrolyte conditions are important in implementing LAI.

Incorporating cover crops into the rotation is a practice applied across many parts of the globe to enhance soil biological activities. In dryland farming, where crop production is highly dependent on rainfall and soil water storage, cover cropping can affect soil water, yet its effects on soil hydrological and biological health require further investigation. The objective of this study was to evaluate the effect of different timing of summer sorghum cover crop termination on soil water, total and labile organic carbon, arbuscular mycorrhizal fungi and their mediating effects on wheat yield. Through on-farm trial, soil characteristics along with wheat biomass, yield and grain quality were monitored. In comparison with the control (fallow), the early terminated cover crop was the most effective at retaining greater soil water at wheat sowing by 1~4% in 0–45cm soil profile. An increase in water use efficiency, yield and grain protein by 10%, 12% and 5% was observed under early termination. Under late terminated summer cover crop, there was 7% soil water depletion at wheat planting which resulted in 61% decline in yield. However, late-terminated cover crop achieved the greatest gain in soil total and particulate organic carbon by 17% and 72% and arbuscular mycorrhizal fungal Group A and B concentration by 356% and 251%. Summer cover crop incorporation resulted in a rapid gain in labile organic carbon, which constituted hotspots for arbuscular mycorrhizal fungi growth, conversely, fungal activities increased labile organic carbon availability. The combined effect of increased soil water at sowing and over the growing season, organic carbon, and microbial activities contributed to greater yield. The findings suggest that summer cover cropping with timely termination can have implications in managing soil water at sowing time and enhancing soil water storage during the season, soil carbon, and facilitating microbial activities while enhancing productivity in the dryland cropping system.