UC Riverside

Use of organic amendments in lieu of more expensive inorganic amendments is increasingly seen as a sustainable alternative for reclaiming salt-affected soils. Moreover, due to the scarcity of fresh waters for agricultural irrigation, alternatives such as use of low quality reclaimed waters and drainage waters are encouraged. The main objectives of this dissertation were (1) to evaluate whether composts and/or biochars can be used to reclaim a saline sodic soil in conjunction with reclaimed water, (2) to understand and quantify the relative contribution of physiochemical and biological factors that aid in saline-sodic soil reclamation, and (3) to evaluate the specific effects of temperature on soil respiration, aggregate stability, hydraulic conductivity and other chemical properties of a saline-sodic soil amended with composts and biochar.

Laboratory incubation and column leaching experiments were used in this research. Organic amendments included, a biosolids co-compost, a greenwaste compost, a woodchip biochar and a dairy manure biochar. Soil properties including wet aggregate stability and saturated hydraulic conductivity were analyzed in relation to cumulative leachate losses of Na+, Ca2+ and Mg2+. Chemical properties such as CEC, ECe, pH, SAR, ESP and exchangeable cations were quantified for soils before and after leaching. Results showed that soil aggregate stability and hydraulic conductivity improvements were greatest with composts. Biochars did not significantly affect soil aggregate stability but increased soil hydraulic conductivity relative to untreated soils. Organic amendments significantly increased Na+ leaching with corresponding decreases in leaching times. Cumulative losses of Ca2+ and Mg2+ were greatest from composts followed by biochars, indicating their potential to contribute divalent cations. Only composts significantly affected soil pH and CEC. Mode of action by biochars was determined to be physiochemical. Composts offer a comprehensive advantage since physiochemical and biological factors act synergistically in those materials. Temperature only significantly affected the soil physical but not chemical properties and these effects were associated only with compost treated soils. Finally, this work showed that simultaneous use of reclaimed water and organic amendments can successfully leach and reclaim a saline-sodic soil.