Effects of Nitrogen Fertilizer Rate and Plant Density on Short-Season Cotton Yield, Nitrogen Use Efficiency and Soil Fertility Using 15n Tracing Technique

Straw returning has been widely used as nitrogen (N) reduction measure in the North China Plain in recent years. But, little is known of the optimal plant density and N application rate of cotton under straw returning by now. In the present study, a short season cotton SCRC66 was used to study the plant density and N application rate on yeild, nitrogen use efficiency (NUE), and N balance and soil fertility of cotton under straw returning. A split-plot design in randomized complete blocks were used in the experiment. The main plots assigned to plant densities (4.50×10 4 , 6.75×10 4 and 9.00×10 4 plants hm -2 ) and the subplots assigned to N application rates (0, 180, 225 and 270 kg N hm -2 ). The results showed that the biological yield increased with increased plant and N application rates, but the harvest index decreased with the increase of plant and N application rates. Therefore, the highest biological yield was found under D 9.00 N 270 , but the highest cotton yield was found under D 6.75 N 225 . The percentage of N absorbed by cotton from 15 N-labeled urea was reduced with the increase of plant density. Excessive N (N 270 ) application rate was not conducive to the improvement of the agronomic nitrogen use efficiency (ANUE) and nitrogen recovery efficiency (NRE) of the 15 N-labeled urea. But, decrease N application rates (N 180 ) consumed soil N because the the difference of N input and output was a negative value at N 180 . The smallest difference of N input and output was found at D 6.75 N 225 . Consequently, the yield, NUE and the stability of soil nutrients considered, the optimal combination of plant density and N application rate in the North China plain was D 6.75 N 225 , because this treatment had the highest cotton yield, but most importantly, it maintained the sustainable production of cotton in the field