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BACKGROUND Nitrogen management of crops, especially when mid‐stage nitrogen is applied, is a key factor affecting the yield and grain quality of rice (Oryza sativa). Here, the timing of mid‐stage nitrogen application was evaluated for its effect on rice grain quality by assessing the morphological structure and physicochemical properties of starch from two japonica rice cultivars growing in fields (Nangeng 9108 and Nangeng 5055). RESULTS The experiment was arranged in a split‐plot design, with the two rice cultivars as the main plot factor and three timings of mid‐stage nitrogen application as the within‐plot factor. Briefly, three applications were made: at the emergence of the top‐sixth‐leaf (ahead), the top‐fourth‐leaf (normal), and the top‐second‐leaf (delayed) of the main stem. Delaying mid‐stage nitrogen application caused the starch granule surface to become uneven and significantly reduced its particle size, whereas it increased the polished rice rate, chalkiness degree, and protein content. Furthermore, the apparent amylose content decreased with a delay in mid‐stage nitrogen application, thereby resulting in higher relative crystallinity, swelling power, water solubility, gelatinization enthalpy, and low retrogradation. Finally, we also found that delaying this nitrogen application lowered the characteristic values of rice flour viscosities, leading to cooking quality deterioration. CONCLUSION These results therefore suggest that delaying mid‐stage nitrogen application enhances the processing and nutritional qualities of japonica rice but evidently has an adverse effect upon its appearance and cooking qualities. © 2020 Society of Chemical Industry

Background and objectives In rice, amylose and protein are the main factors that influence eating quality. The aim of this study was to determine the influence of the ranges in amylose and protein variation on rice eating quality and to explore the characteristics of amylose and protein in high eating‐quality rice varieties. A total of 105 japonica rice varieties (lines) from the middle and lower reaches of Yangtze River were studied. Findings When amylose content (AC) ranged from 7.35% to 19.98% and protein content (PC) ranged from 6.04% to 9.32%, amylose and protein were significantly (p < .01) negatively correlated with rice appearance, adhesiveness, balance degree, and taste value, and significantly (p < .01) positively correlated with hardness. However, when AC varied between 7.35% and 12.50% or between 14.11% and 19.98%, the eating characteristics had no significant correlation with AC; instead, they were significantly correlated with protein content (PC). PC had no significant influence on eating characteristics when it ranged from 7.86% to 9.32%. To improve eating quality (i.e., taste value > 60), PC in varieties with high AC (14.11%–19.98%) should be < 6.98%, and AC in varieties with high PC (7.86%–9.32%) should be < 12.67%. Conclusions The results showed that the relationships among AC, PC, and eating quality were affected by the ranges of AC and PC variation. Rice varieties of the low amylose and low protein (LALP) combination should be the best choice for the high eating‐quality variety in the middle and lower reaches of Yangtze River. Significance and novelty Amylose and protein should be considered as the primary and secondary screening indices, respectively, in the selection and breeding of good eating‐quality rice varieties.

A mixture of controlled-release nitrogen (N) fertilizers (CRNFs) and conventional urea (CU) as a single application of basal fertilizer could simplify fertilization in rice cultivation from the traditional and more labor-intensive fertilization strategy of multiple applications of nitrogen. However, the reported benefits of this combined approach in increasing rice yield have varied substantially for various reasons, including that various types of rice are characterized by different N requirements to obtain high yield. In this study, two late japonica rice cultivars, Jia58 (J58) and Jia67(J67), were used to determine the best combination of one of two short-acting CRNFs (release periods were 40 and 60 days) and one of three long-acting CRNFs (release periods were 80, 100 and 120 days) to apply with the CU as a one-time application of basal fertilizer. Six combinations of CRNFs were established based on their release periods: A1, 40 + 80 days; A2, 40 + 100 days; A3, 40 + 120 days; B1, 60 + 80 days; B2, 60 + 100 days; and B3, 60 + 120 days. CU applied split at basal, tillering and panicle differentiation stages, respectively as control (CK). The effects of the different treatment combinations of CRNFs on late-rice grain yield, N accumulation and N-use efficiency in a two-year field experiment were determined. Results showed that, the A2 treatment achieved the same yield as that of CK, and yield of the B2 treatment exceeded the yield of CK. Yield of J58 applied with B2 was 7.35% higher in 2018 and 7.40% higher in 2019 than that of the corresponding yield of CK; yield of J67 applied with B2 was 6.05% higher in 2018 and 6.87% higher in 2019 than that of CK. Compared with other CRNF treatments, the release of N from A2 and B2 was most synchronized with nitrogen uptake by the two cultivars, which indicates that fertilizer combination completely met the nitrogen demands during each growth stage of rice. Rice of the A2 and B2 treatments had higher N accumulation, higher aboveground biomass accumulation and LAI (leaf area index) at the heading and maturity stages and higher photosynthetic activity than those of other CRNF treatments. In conclusion, for late japonica rice in China, the application of the A2 and B2 treatments as optimal type of CRNF can achieve labor saving and yield increasing simultaneously in rice production.

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