Qun Hu1, Qiuyuan Liu1,2, Weiqin Jiang1, Shi Qiu3, Haiyan Wei1, Hongcheng Zhang1, Guodong Liu1, Zhipeng Xing1, Yajie Hu1, Baowei Guo1, Hui Gao1. 1. Jiangsu Key Laboratory of Crop Genetics and Physiology/Jiangsu Co-Innovation Center for Modern Production Technology of Grain Crops/Agricultural College, Yangzhou University, Yangzhou, China. 2. Agricultural College, Xinyang Agriculture and Forestry University, Xinyang, China. 3. Provincial Key Laboratory of Agrobiology/Institute of Crop Germplasm and Biotechnology/Jiangsu Academy of Agricultural Sciences, Nanjing, China.
Abstract
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.
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.