Effect of biochar and attapulgite amendment on saline soil hydraulic parameters and shrinkage

Saline soil reduces soil productivity and exacerbates food security problem. Therefore, it is increasingly necessary to find sustainable farming practices for soil and water conservation. In this regard, conditioning the soil with biochar (BC) or attapulgite (ATP) has been proved as a feasible method of improving water conservation and soil hydraulic characteristics. However, the interactive effect of BC and ATP on saline soil is still unclear. The objective of this study was to investigate the effect of BC and/or ATP on water retention, pore size distribution, hydraulic characteristic parameter, and shrinkage strain of saline soil through laboratory trials. For this purpose, BC and/or ATP were added to the loam soil at three levels of 0%, 2%, and 4% by weight, and saturated in the sodium chloride solution with a concentration of 5 g L−1. Results showed that the Van Genuchten model accurately fitted the obtained soil water characteristic curve (R2 > 0.99). BC and/or ATP amendments increased saline soil water retention capacity compared to the unamended soil. Soil water retention capacity increased as the ATP application rate increased. The saturated water content, field water holding capacity, soil microporosity, and soil retention effect of 2%BC combined with 4%ATP were higher than other treatments. BC facilitated the reduction of soil shrinkage, and ATP increased soil shrinkage. Axial shrinkage strain was negatively correlated with the application rate of BC, and positively correlated with ATP. 4%BC combined with 2%ATP had the least shrinkage strain. The present results could serve as a theoretical foundation for soil amendments to improve soil quality.