Buried layers change soil water flow and solute transport from the Yellow River Delta, China

Abstract

For the limitation of techniques on the saline soil improvement, the effect of a new method with some effective materials on saline soil improvement was studied by soil column experiment. Biochar and wood fibre were used as a buried layer to identify their effects on the saline soil reclamation. Soil samples were packed in each column (height, 130 cm; diameter, 20 cm). A tape measure (length, 100 cm) was fixed vertically to the outer wall of each soil column; it was used to record the location of the wetting front during infiltration. Biochar and wood fibre were inserted at depths of either 30 cm or 50 cm (thickness in each treatment, 2 cm). Soil columns were irrigated once with 15 L of brackish water (2 g/L). Soil water content and salt content were measured with a TRIME-PICO sensor at the 25, 60 and 100 cm layers, and Mariotte’s bottle was used at the 100-cm layer to measure the underground water level. Wood fibre and biochar used as the buried layer was found that they caused a breakdown in the continuity of capillary movement and salt reduction. Wood fibre and biochar were able to retard the rate of water infiltration at 0–30-cm depth, for high water potential created when the buried layer contained sufficient water; it improved the more water infiltration than evaporation. Thus, it could serve to increase the salt leaching efficiency during the longer time scales of soil water infiltration; results showed that the buried layer was at 30-cm depth; the desalting rates were 3.69% (biochar) and 29.38% (wood fibre); the desalting rates were 4.76% (biochar) and 17.07% (wood fibre) when buried layer at 50 cm. And, the better performance in soil water infiltration and salt reduction was caused by a higher pore width, abundant fibrous tissue and saturation moisture content (Ɵs). The buried layer can improve the soil water infiltration process, especially when the wood fibre layer was at 30 cm. Both biochar and wood fibre layers could limit salt accumulation in surface soil, indicating that the continuity of capillary movement was broken after embedding the interlayer; wood fibre was superior to biochar in this regard. This study provides a new method on the saline soil improvement that could improve the mulching development, and the effect of the evaporation could be further considered by the buried layer.