Effect of soil salinity and nitrogen fertilizers on net photosynthetic productivity of cotton crop

This study investigates the net photosynthetic productivity (NPP) of cotton (Gossypium hirsutum L.) under varying levels of soil salinity and nitrogen fertilization across key phenological stages: budding, flowering, and boll formation. Experimental data demonstrate that NPP significantly increased with the application of phosphorus-potassium base fertilizers (P175K125) and nitrogen at rates of 100–350 kg/ha compared to control plots across all salinity levels. On non-saline soils, NPP reached a maximum of 14.4 g/m²/day during boll formation at 350 kg/ha nitrogen, representing a 282% increase over the control. Under weakly saline conditions, peak NPP was 13.9 g/m²/day, while moderately and strongly saline soils showed reduced productivity, peaking at 10.6 and 9.7 g/m²/day respectively. Salinity negatively influenced photosynthetic efficiency, particularly under control conditions, where NPP in the budding phase was as low as 2.9 g/m²/day on strongly saline soils. Nonetheless, even under salinity stress, nitrogen supplementation significantly mitigated adverse effects, enhancing photosynthetic performance. The flowering phase consistently exhibited higher NPP compared to budding, underscoring its physiological importance in cotton development. The application of 250–350 kg/ha nitrogen provided optimal results across all salinity conditions, indicating its effectiveness in improving photosynthetic activity and plant growth. The findings emphasize the critical role of balanced mineral nutrition, particularly nitrogen, in sustaining cotton productivity under saline conditions, and contribute to developing efficient agronomic strategies for managing salinity stress in arid and semi-arid regions.