The Presence of the Biochar Interlayer Effectively Inhibits Soil Water Evaporation and Salt Migration to the Soil Surface

To reveal the mechanisms of water conservation and soil salinity control in the biochar interlayer, the effects of biochar addition as an interlayer on soil water infiltration, evaporation, and salt transport were studied. Through the indoor soil-column simulation test, soil columns were set up by packing homogeneous soil (CK) and biochar spacers into columns at different burial depths of 10, 20, and 30 cm. The biochar interlayer decreased the infiltration capacity of the soil, with the average infiltration rate decreasing from 0.72 cm·h−1 to the ranges of 0.39–0.48 cm·h−1 in the CK soil column, and salt leaching efficiency was improved. The salt content in the bottom layer of soil in the CK column was reduced to within the range of 19.96–47.46% compared with that in the barrier soil column. The presence of the biochar interlayer improved the distribution of soil water and salt. The soil water content in the upper layer above the interlayer was around 7.79–13.68% higher than that in CK, whereas the average salt content was 6.44–60.40% lower than that in CK. The biochar interlayer inhibited soil water evaporation, and cumulative evaporation in this layer decreased by 32.34–42.10% compared with that in CK. The salt accumulation in the interlayer in the soil column decreased within the range of 16.36–51.36% compared with that in the CK soil column. The biochar interlayer could not only retain water for a long time, but also adsorb the salt leached from the upper layer, and thus, inhibit the reverse salt flux from the lower layer. The creation of the biochar interlayer of 30 cm could play a role in soil salinity control and water conservation, and can also provide a basis and reference for the improvement of saline-alkali farmland in arid and semi-arid areas.