Compensation effects of nitrogen fertilizer on yield and quality of cotton under insufficient irrigation

Objectives Insufficient irrigation might cause adverse effect on cotton growth, yield and quality. This paper studied the suitable nitrogen fertilizer rate to alleviate the adverse impact of insufficient irrigation.

Methods Using cotton cultivar of ‘Xin Lu Zhong No.54’ as tested material, a split plot experiment was conducted. The main factor was total irrigation amount of 2800 m³/hm² (insufficient irrigation) and 3800 m³/hm² (sufficient irrigation); the deputy area was nitrogen levels of 0, 150, 300 and 450 kg/hm². The cotton growth and lint quality were determined, and water use efficiency was calculated at harvest stage.

Results Under the same treatment levels of nitrogen, the maximum accumulation rate of dry matter and nitrogen and the inflexion point in insufficient irrigation arrived earlier than those in conventional irrigation; the dry matter and nitrogen accumulation amount and the maximum accumulation rate, the allocation ratio of dry matter and nitrogen in reproductive organ, the transfer efficiency of nitrogen to reproductive organ, the seed cotton yield and quality were lower; but the seed cotton yield increase rate, the nitrogen agronomic use efficiency, the water and nitrogen use efficiency were higher. Under both the irrigation treatments, with the increase of nitrogen fertilizer rate, the maximum accumulation rate and the inflexion point of dry matter and nitrogen arrived the earliest in N450, followed by N300, N150, N0 in turn; the dry matter and maximum N accumulation amount and accumulation rate, the maximum growth characteristic value, the allocation ratio of dry matter and nitrogen to the reproductive organ, the transfer efficiency of nitrogen to reproductive organ, the seed cotton yield and quality and water use efficiency were in order of N300 > N450 > N150 > N0; the seed cotton yield increase rate, the nitrogen agronomic use efficiency and nitrogen use efficiency were in order of N300 > N450 > N150. The compensation effect of N fertilizer showed the trend of firstly increase and then decrease with the increase of the nitrogen rate under insufficient irrigation, the compensation effect of N300 treatment was the most significant. Compared with sufficient irrigation treatment, the compensation effect mainly showed that the maximum accumulation rates of dry matter and nitrogen were increased by 1.9% and 3.1%, the allocation ratio of dry matter to the reproductive organ and the transfer efficiency of nitrogen to reproductive organ were raised by 24.0% and 5.1%, water and nitrogen use efficiencies were enhanced by 6.1%–8.8% and 17.3%–17.9%, the seed cotton yield increase rate was increased by 6.1%–8.8%, the fiber length, the fiber uniformity and fiber strength were increased by 4.3%–20.1% and 5.7%–7.3% and 2.2%–12.5%, respectively. The effect of nitrogen fertilizer on cotton growth was greater than that of water.

Conclusions At N rate of 300 kg/hm², there is no significance difference in the cotton yield and fiber quality between the insufficient irrigation and sufficient irrigation. With this N rate under insufficient irrigation condition, cotton plants can keep normal growth, the dry matter and N accumulation are suitable, and their distribution rates are high, so the water and nitrogen use efficiencies are high. Considering the water shortage in the south of Xinjiang, applying nitrogen of 300 kg/hm² could compensate the adverse impact of insufficient irrigation and increase cotton fiber quality, water and nitrogen use efficiency is the highest, and cotton fiber quality is increased, water and nitrogen use efficiency is the highest, and water saving is 26.3%.