Long-term mulched drip irrigation enhances cotton yield by improving soil quality, microbial community structure, and N conversion

Long-term mulched drip irrigation can improve cotton yield, but its effectiveness depends on how long the land has been cultivated, and the mechanisms behind this relationship are not yet fully understood. In this study, the uncultivated wasteland was used as a control to systematically assess how varying lengths of cotton cultivation influence soil physicochemical properties, microbial community dynamics, and nitrogen (N) transformation pathways. The results revealed that: (1) converting wasteland into cotton fields significantly improved soil quality, with survival rate and yield increasing by 10.04 % and 13.60 %, respectively, in fields cultivated for 22 years compared to those cultivated for 8 years; (2) long-term cultivation markedly enhanced microbial diversity and the relative abundance of beneficial taxa associated with crop growth; (3) genes related to fungal glutamate synthesis and ammonification, as well as bacterial nitrogen fixation and nitrification, were significantly upregulated, while those involved in bacterial glutamate synthesis, nitrite reduction, denitrification, and ammonification were downregulated; (4) core microbial taxa exhibited significant positive correlations with nitrogen cycle–related functional genes; (5) fungal diversity showed a strong positive correlation with cotton yield, whereas bacterial diversity did not. In summary, long-term cultivation can regulate microbial community structure by improving soil quality, thereby enhancing cotton yield by promoting fungal-driven nitrogen cycling and suppressing bacterial denitrification.