Effects of nitrogen application rate on nitrogen absorption and utilization, and fate of nitrogen in soil-cotton system

Objectives In order to clarify the effect of nitrogen application on high-yield cotton fields in this region. It provides a theoretical basis for scientific nitrogen application.

Methods The ¹⁵N tracer method was used in the pot experiment. It was conducted with Liaomian 6 as material, five nitrogen rates of 0, 2, 4, 6 and 8 g/pot were designed, and recorded as N0, N2, N4, N6 and N8, respectively. The experiment was conducted to study the effects of nitrogen application rate on nitrogen absorption and utilization, and fate of nitrogen in soil-cotton system.

Results At harvest stage, with the increase of nitrogen application, the yield of seed cotton increased first and then decreased. The seed cotton yield and harvest index of N2 and N4 were significantly higher than those of other treatments. The accumulation of dry matter and nitrogen increased, and they all reached the maximum in N8. At the same time, the N agricultural efficiency decreased significantly, and the N recovery efficiency increased first and then decreased. It achieved the maximum value in N4, but there was no significant difference with taht in N2. The uptake of fertilizer ¹⁵N increased significantly, and ¹⁵N recovery rate showed a downward trend in cotton plant. Positive excitation effect was produced in all nitrogen application treatments. With the increase of nitrogen application, ¹⁵N residue and ¹⁵N loss of fertilizer increased significantly. After topdressing, ¹⁵N residue and ¹⁵N loss increased while ¹⁵N residue rate and loss rate decreased. This indicated that the absorption and utilization of ¹⁵N increased after anthesis, and the recovery rate of ¹⁵N of cotton plant increased, resulting in the decrease of residue rate and loss rate. The proportion of cotton nitrogen from soil was 66.35%–81.87%, and the priming effect of soil nitrogen was 114.44%–125.86%.

Conclusions The recovery rate of ¹⁵N was 58.65% , the residual rate of ¹⁵N was 23.67% and the loss rate of ¹⁵N was 17.68% when nitrogen application rate was N2. N2 can guarantee high cotton yield, reduce the input of nitrogen fertilizer, reduce losses and improve the absorption and utilization of nitrogen fertilizer. In N2 treatment, soil nitrogen pool reaches a balanced state, which could not only achieve high yield but also meet the needs of environmental friendliness.