Long-term stubble return and subsoiling enhance cotton yields in coastal saline-alkali soils by improving soil conditions and photosynthetic characteristics

Stubble returning and subsoiling are agronomic practices used to ameliorate saline-alkali soils, while photosynthesis is a fundamental physiological process underpinning crop yield formation. Long-term implementation of stubble returning and subsoiling can improve soil fertility in coastal saline-alkali cotton fields, thereby promoting cotton growth and yield. However, the photosynthetic response of cotton to long-term conservation tillage under saline-alkali conditions remains insufficiently understood. To investigate the effects of long-term conservation tillage on soil physicochemical properties, cotton photosynthetic performance, dry matter accumulation, nutrient uptake, and lint yield in coastal saline-alkali fields, four treatments were established: conventional tillage (CK), subsoiling (S), stubble returning (R), and the combination of stubble returning and subsoiling (RS). The results showed that, compared with CK, the RS treatment significantly reduced soil pH by 6.6%-7.7% and soil salt content by 21.2%-26.1% (<italic>P</italic> &lt; 0.01). At full bloom and boll-setting stages, net photosynthetic rate (<italic>P</italic>_n), stomatal conductance (<italic>G</italic>_s), and relative chlorophyll content (SPAD value) increased by 15.9%, 42.9%, and 12.7%, respectively (<italic>P</italic> &lt; 0.05). During the boll-opening period, canopy photosynthetically active radiation (PAR), dry matter accumulation, and nitrogen uptake increased by 11.8%, 59.8%, and 72.0%, respectively (<italic>P</italic> &lt; 0.05). Moreover, lint yield increased by 56.2% (<italic>P</italic> &lt; 0.01). Lint yield was significantly positively correlated with transpiration rate (<italic>T</italic>_r), stomatal conductance (<italic>G</italic>_s), and PAR (<italic>r &gt;</italic> 0.5, <italic>P</italic> &lt; 0.05). In conclusion, long-term stubble returning and subsoiling effectively improve the soil environment in saline-alkali fields, enhance cotton photosynthetic capacity, and significantly increase lint yield. This integrated conservation tillage strategy offers a practical and effective approach to promoting cotton growth and improving productivity in coastal saline-alkali regions.