Long-term cotton stubble return and subsoiling increases cotton yield through improving root growth and properties of coastal saline soil

Short-term cotton stubble return increased cotton yield in coastal saline soil. Due to high groundwater level, salt return from deep soil would affect the sustainability of long-term cotton stubble return on the improvement of soil properties and yield in coastal saline soil. However, subsoiling can cut off the capillary and inhibit the seasonal salt return. Here we quantified the effects of long-term cotton stubble management (removal or return) and tillage (non-subsoiling or subsoiling) on soil properties, root growth and cotton yield. Cotton yield increased 36.3.% after stubble return than after stubble removal, and enhanced 22.8% after subsoiling compared to nonsubsoiling. Structural equation model showed that stubble return increased cotton yield by reducing salt content, pH and bulk density, increasing total porosity, small macro-aggregates, root weight density (RWD) in the topsoil, total organic carbon (TOC), nitrogen (N), and their fractions in both layers, while subsoiling increased yield by reducing salt content, pH and bulk density, and increasing total porosity, small macro-aggregates, RWD in the subsoil. Compared to stubble removal, TOC, dissolved OC (DOC) and microbial biomass C (MBC) increased 54.3%, 33.2% and 24.8% in the topsoil, 37.4%, 18.8% and 39.1% in the subsoil after stubble return. Stubble return increased TN and its fractions in the topsoil, and DON, MBN, ammonium nitrogen in the subsoil compared to stubble removal. Maximum root shoot ratio can be obtained only when two measures are combined. Combination of stubble return and subsoling increased yield by optimizing soil properties and root growth in two layers, which is much better than only stubble return or subsoiling. Our analyses demonstrate combination of cotton stubble return and subsoiling can increase cotton yield and be widely applied as an effective measure in coastal saline fields.