Subsoiling increases soil carbon and wheat yields by altering the deep soil and the hydrolase to oxidase ratio under saline water irrigation

Carbon pool management index (CPMI), which combines carbon pool capacity and carbon activity, is crucial for understanding carbon flow in soil. It is essential to determine whether changes in soil carbon components due to saline irrigation diminish the CPMI, which could negatively impact soil stability. A study conducted over two winter wheat and two spring wheat seasons in the arid northwest region investigated how soil enzyme activity and carbon storage in both surface and deep soils respond to saline irrigation under rotary and subsoiling management. During the vegetative growth stage, subsoiling promoted tiller differentiation. In the reproductive growth stage, saline irrigation enhanced the tiller success rate but reduced the ratio of spikes to dry matter (DM). Specifically, in the 0–20 cm soil layer, subsoiling increased the levels of clay, silt, and SOC. This enhancement resulted in improved soil hydrolase and oxidase activity, raising CPMI for winter and spring wheat by 12.09 % and 8.00 %, respectively. Additionally, the ratio of spikes to DM improved by 13.90 % and 9.38 %, resulting in overall yield increases of 15.88 % and 15.77 %. Under saline irrigation, subsoiling for winter and spring wheat effectively utilized high-quality substrates in the 20–40 cm soil layer to construct a stable C pool. This was achieved by enhancing overall enzyme activity and the hydrolase to oxidase ratio, thereby attenuating the adverse effects of reduced labile organic carbon components caused by decreased clay and silt proportions from saline irrigation. These results support the use of subsoiling as a resilient tillage strategy under saline irrigation.