Effects of earthworm casts on water and salt movement in typical Loess Plateau soils under brackish water irrigation

Soil salinization severely degrades agricultural land and significantly impacts agricultural productivity. Earthworm casts, as a pollution-free improver, can effectively enhance the structure and properties of soil; however, their effects on water and salt movement in soil, under brackish water irrigation, remain unclear. In this study, we conducted laboratory experiments to investigate the effects of earthworm cast treatments under four application rates (untreated, 1%, 3%, and 5% of soil weight) on water and salt movement in anthrosols (CS) and cambisols (AS) from the Loess Plateau. The application of earthworm casts was found to inhibit soil infiltration and evaporation, except for the 1% treatment in CS; inhibition also increased with more concentrated treatments. Compared to that in untreated soil, the infiltration rate and cumulative evaporation in cast-treated CS decreased by 23.9-32.2% and 5.1-9.8%, whereas in AS, they decreased by 17.6-28.5% and 8.6-20.7%. The application of earthworm casts significantly reduced the electrical conductivity of the upper 20 cm of soil, and the reduction increased with more concentrated treatments. Compared with untreated soil, the application of earthworm casts significantly reduced the sodium absorption ratio in the upper 0-20 cm by 15.6-31.1% in CS and 12.2-28.1% in AS. Applying earthworm casts significantly reduced the exchangeable sodium percentage of soil at 0-20 cm by 16.5-25.9% in CS and 13.5-22.5% in AS. Therefore, the application of earthworm casts effectively alleviated soil salinity and sodicity in both soil types by reducing the salt content in the upper 0-20 cm under brackish water irrigation.

Automated summary

The application of earthworm casts can effectively reduce soil salinity and sodicity by decreasing the salt content in the upper soil layers under brackish water irrigation. Additionally, earthworm casts improve soil structure and properties, inhibiting soil infiltration and evaporation, with effects increasing at higher application rates.