Abstract:

Through field experiments, five treatments were set up: no nitrogen fertilizer (PK), conventional fertilization (NPK), a single base application of slow/controlled release urea (T1), 80% slow/controlled release urea + 20% urea as a single base application (T2), and 80% slow/controlled release urea as base fertilizer + 20% urea as top dressing (T3). These treatments were used to study the impact of different nitrogen applications on the grain yield and its components, nitrogen fertilizer efficiency, and soil nitrogen supplying capacity in double-cropping rice. The results showed that compared with conventional fertilization, the application of slow/controlled release fertilizer significantly increased rice yield, especially the T2 treatment. T2 had the highest effective panicle count for both early and late rice, followed by T1, T3, and NPK, with PK being the lowest. The nitrogen uptake of grain in the early rice from slow-release fertilizer treatments was significantly higher than that of NPK treatment by 18.5% to 26.0%, and the nitrogen uptake of straw was significantly increased by 12.7% to 20.9%; In the late rice, the nitrogen uptake of grain was also significantly higher than that of NPK treatment by 24.4% to 28.8%, and the nitrogen uptake of straw was significantly increased by 18.4% to 39.1%. The nitrogen uptake of straw in the T3 late rice was significantly higher than that in T1 treatment and T2 treatment by 17.5% and 16.1%, respectively. Nitrogen fertilization caused nitrogen accumulation in the soil, especially in the NPK treatment, where the nitrogen surplus was much higher than that in the treatments using slow/controlled release fertilizers. Whether in early or late rice, the apparent nitrogen use efficiency of the T3 treatment was the highest, followed by T2 treatment, T1 treatment, and the lowest in NPK treatment. Compared with NPK treatment, the soil hydrolyzable nitrogen content in the slow/controlled release fertilizer treatments increased significantly by 12.8% to 25.4%, ammonium nitrogen content increased by 177.7% to 217.8%, and nitrate nitrogen content increased by 94.2% to 120.0%. The hydrolyzable nitrogen content and nitrate nitrogen contents in the T1 treatment were significantly higher than those in T3 by 11.1% and 13.3%, respectively, and the ammonium nitrogen content was higher than those in T2 and T3 by 10.0% and 14.5%, respectively. In summary, based on straw return, under the same amount of nitrogen applied, the fertilization method using 80% controlled-release urea combined with 20% urea as a single base application can significantly enhance soil nitrogen supplying capacity while ensuring that the rice grain yield does not decrease, compared with the conventional method of one base and two top dressing applications.

Key words: double-cropping rice, controlled-release urea, nitrogen fertilizer, efficiency, nitrogen supplying capacity