Coupling effects of water and nitrogen on dry matter accumulation, nitrogen uptake and water-nitrogen use efficiency of cotton under mulched drip irrigation

Field trials were conducted to study the coupling effects of water and nitrogen on nitrogen uptake and dry matter accumulation of cotton at different growth stages, lint yield and water-nitrogen use efficiency. Cottons were grown under three nitrogen application levels and two irrigation levels making six combination treatments. The results show that during the flowering and boll-setting stage, water and nitrogen supply can promote root and shoot growth of cotton. At the boll opening stage, nitrogen supply has no effects on above-ground biomass, while root dry weight is maximum at the 276 kg/ha nitrogen application level under water stress. Root dry weight is reduced with the nitrogen supply, and the above-ground dry weight and nutrient uptake are maximum at the 276 kg/ha nitrogen level under sufficient water supply. From the flowering and boll setting stage to the boll opening stage, too much nitrogen supply can inhibit root and shoot dry matter accumulation. The highest points of lint yield and water-nitrogen use efficiency are different. The lint yield and nitrogen use efficiency are increased, water use efficiency is decreased under the increase of irrigation amount. Under water stress, nitrogen supply has no effects on lint yield, but nitrogen use efficiency is decreased and water use efficiency is increased when the nitrogen level is increased. Under sufficient water supply, the lint yield is maximum at the 276 kg/ha nitrogen level. The water-nitrogen coupling N276W600 obtains maximum lint yield, and relatively high water-nitrogen use efficiency.