Influence of optimized nitrogen management on the quality of medium hybrid rice under different ecological conditions

The effects of different nitrogen (N) treatments on rice quality were studied at two different ecological sites (Wenjiang and Shehong), using single-factor experiment with a randomized block design and 'F You 498' as the test material. The results showed that the milling quality, appearance, and grain crude protein content were better in the Wenjiang rice. In the Shehong rice, the peak viscosity and breakdown viscosity were higher and the setback viscosity was lower; the cooking and eating qualities were better and the amylose content was higher. With N fertilizer applied, the rice milling quality and amylose and grain crude protein contents were significantly increased, and the breakdown viscosity was significantly decreased. At the same time, N fertilization increased the peak viscosity and reduced the setback viscosity of Shehong rice, whereas it improved the appearance, decreased the peak viscosity, and increased the reduction value of Wenjiang rice. Compared with the fertilization practices of farmers, the optimal N fertilizer treatments (ONM1:optimized N management; ONM-_N1:optimized N management with 15% N reduction; and ONM+_N1:optimized N management with 15% N increase) and optimized N management of polyaspartic acid-urea (PASP-urea) treatment increased the amylose and grain crude protein contents. Optimal N fertilizer treatment reduced the chalky rice rate and chalkiness ratio, and improved the appearance of Wenjiang rice. At both ecological sites, the optimal N fertilizer treatment reduced the peak viscosity and breakdown viscosity, increased the setback viscosity, and worsened the cooking and eating qualities of the rice. At the same time, it increased the milled rice rate of Shehong rice and the head rice rate of Wenjiang rice. In comparison with the ONM1 treatment, PASP-urea treatment reduced the milled rice ratios and head rice rates of the two types of rice and the chalky rice rate of Wenjiang rice, whereas it increased the chalky rice rate and chalkiness ratio of Shehong rice, worsening its appearance. At the same time, PASP-urea applied at the basal stage only and spilt-applied at the basal stage and at panicle initiation reduced the amylose and grain crude protein contents. Optimized N management of PASP-urea treatment reduced the peak viscosity and breakdown viscosity of the two rice types and the amylose content of Wenjiang rice, whereas it increased the grain crude protein contents of the two rice types and the amylase content of Shehong rice. Compared with the OMN1 treatment, the ONM-_N1 and ONM+_N1 treatments reduced the amylose contents and the head rice rates of the two rice types and the chalky rice rate of Wenjiang rice, whereas they increased the chalky rice rate and chalkiness ratio of Shehong rice. Compared with that of PASP-urea applied at the basal stage alone and spilt-applied at the basal stage and at panicle initiation, optimized N management of PASP-urea treatment significantly decreased the chalkiness ratio, peak viscosity, and breakdown viscosity, and increased the setback viscosity and grain crude protein contents. At the same time, it reduced the head rice rate and increased the chalky rice rate and amylose content in Wenjiang rice, whereas it reduced the chalky rice rate and increased the head rice rate in Shehong rice. Overall, in terms of the milling quality, appearance, starch RVA, amylose content, and grain crude protein content, the two applications of PASP-urea fertilizer treatment resulted in better comprehensive qualities in Shehong rice, whereas optimized N fertilization treatment gave better comprehensive qualities in Wenjiang rice.