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In order to optimize N application and understand how the different combinations of water and N management affect grain filling characteristics and yield, we designed three irrigation regimes (W1 submerged irrigation, W2 alternate irrigation, W3 dry cultivation), and different N application strategies at 180 kg ha−1 in 2010 and 2011. The relationship between grain filling characteristics and grain yield formation were respectively investigated. The results revealed that there were obvious interacting effects of irrigation regime and N application strategies on grain yield and grain-filling characteristics as well. Compared with W1 and W3 treatments, under W2, the N-fertilizer should account for 30% base, 30% tillering, and 40% panicle fertilizer with the last being applied equally at 4th and 2nd leaves emerged from the top. Correlation analysis revealed that grain filling rate during middle grain-filling stage was the largest and contribute more than 50% to grain-filling. Grain yield was significantly related to grain filling rate (Gmax or Gmean), final weight of a kernel (A), and mean grain filling rate (MGR) of the early, mid and late stages during grain filling in inferior spikelets, which is the important reason for water and N coupling effect further to increase yield and fertilizer use efficiency. [ABSTRACT FROM AUTHOR]

Abstract: The water and nitrogen (N) managements play a vital role in hybrid rice production aimed at high yield, high nitrogen use efficiency (NUE), and water-saving irrigation. In order to optimize N application and understand how the different combinations of water and N management affect yield and the relative physiological parameters, we designed three irrigation regimes, standing irrigation (W1), alternation irrigation (W2), and dry cultivation (W3), combined with different N application managements at 180kgha−1 of total N condition in our study. The relationship between yield or NUE and ammonia assimilation enzyme activities, photosynthetic rate and root activity were respectively investigated. Our data revealed that there were obvious interacting effects of irrigation regime and N application strategies on grain yield and NUE as well. Our correlation analysis revealed that the grain yield or NUE was significantly related to ammonium assimilation enzyme activities, photosynthetic rate, and root activity, respectively, at several rice growth stages. Our correlation analysis also revealed that the grain yield was significantly related to the N uptake and utilization, and that the root activity was significantly related to the ammonium assimilation enzymes and photosynthetic rate. Further more, we found that the ammonium assimilation enzyme activities and the photosynthetic rate in flag leaves, or root activity at heading stage was able to be used as indicators for grain yield, total N accumulation, and NUE as well. These results suggest that the N application strategy should be adjusted according to different irrigation regimes in order to obtain the highest yield and the best NUE. Under standing irrigation, on the basis of 40–60% base-tiller N fertilizer, panicle N-fertilizer should account for 40–60% applied equally at 4th and 2nd leaves emerged or 3rd and 1st leaves emerged from the top. Under alternation irrigation, the N application ratio should be split into 30% base, 30% tillering, and 40% panicle fertilizer with the last being applied equally at 4th and 2nd leaves emerged from the top. Under dry cultivation, however, panicle N-fertilizer should account for 20–40% applied equally at 5th and 3rd leaves emerged from the top. [Copyright &y& Elsevier]

BACKGROUND: Chalkiness in rice reduces its market value and affects consumer acceptance. Research on the mechanism of chalkiness formation has focused primarily on the activity of key enzymes of carbon metabolism and starch accumulation. The relationship between the formation of chalkiness induced by N fertilizer and rice starch's multi‐level structure and thermal properties still needs to be fully elucidated. RESULTS: In this study, the rates of chalky grains and degree of chalkiness decreased with the increase in N fertilizer dosage. This was attributed to an increased proportion of short chains, ordered structure carbon chains, small starch granules, and branched starches, and a higher degree of crystallinity and ΔHg in protein, and a decreased proportion of amylose, large starch granules, and weighted average diameter of starch granule surface area and volume. Application of N fertilizer promoted an increased proportion of short‐branched chain amylopectin to develop a more ordered carbohydrate structure and crystalline lamella. These effects enhanced the normal development and compactness of starch granules in grains, and improved their arrangement morphology, thereby reducing the chalkiness in rice. CONCLUSION: These changes in starch multi‐level structure and protein improve the physicochemical characteristics of starch and enhance the fullness, crystallinity and compactness of starch granules, while synergistically increasing the regularity and homogeneity of starch granules and thus optimizing the stacking pattern of starch granules, leading to a reduction in rice chalkiness under nitrogen fertilization and thus improving the appearance of rice. © 2023 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Rice yields have stabilized in the Chengdu Plain, and the implementation of integrated paddy field farming has shown potential for enhancing resource utilization. However, further investigation is required to clarify its impact on production sustainability. Accordingly, this study compared grain yields, energy use, greenhouse gas emissions, and economic benefits of single cropping rice (SCR), rice-duck symbiosis (RDS), and rice-fish symbiosis (RFS) over a three-year period (2018–2020). The grain yields were 16.24%–23.96 % higher in SCR than in RDS and RFS, but nitrogen fertilizer use was reduced by 31.93%–32.15 % in RDS and RFS, and the partial factor productivity of nitrogen was increased by 21.96–23.82 %. RDS and RFS required 1.87–2.00 times more energy than SCR and were only 55.36%–57.80 % as efficient as SCR. They also had higher CO 2 (36.10%–42.20 %) and CH 4 (8.01%–28.88 %) emissions but lower N 2 O (0.02%–21.18 %) emissions than SCR. Economically, RDS and RFS produced 1.30–1.48 times higher net benefits with 1.44–1.47 times higher costs than SCR. The benefit-cost ratio of RFS was comparable to SCR and 11.38%–11.87 % higher than RDS. In summary, RDS and RFS consume more energy (feed accounts for more than half) but provide higher yields and better-quality proteins, which are crucial to improving farmer motivation and ensuring protein availability. [Display omitted] • A 3-year field experiment was conducted to assess integrated paddy field farming. • Yields, energy use, greenhouse gas emissions, and economic benefits are assessed. • Rice-fish symbiosis is a low-pollution, high-yield farming mode. [ABSTRACT FROM AUTHOR]