Effects Of Nitrogen Levels And Soil Moisture During Grain Filling On Grain Quality Of Rice

Soil moisture and nitrogen (N) nutrient are the principal factors affecting rice quality. Elucidation of their influences and coupling effects on the quality would have great significance in conducting the cultivation for high yielding, good quality and high efficiency. In this study, a typical indica hybrid Shanyou 63 and a japonica cultivar Wuyujing 3 were used as materials, and were field-, pot- or tank-grown. The effects of N levels and soil moisture during grain filling and their coupling effects on rice qualities were investigated. The main results are as follows:1. The plants were field-grown. The amount of N, ranged fron 0 to 40 g/m~2, showed no significant effect on brown rice percentage, milled rice percentage, kernel length/kernel width, and amylose content. The protein content was increased with the increase in the amount of N application. The head rice percentage, peak viscosity, and values of breakdown in rapid viscosity analyzer (RVA) profiles were increased, whereas chalky grain percentage, chalkiness, setback values were reduced, when the amount of N application was from 0 to 16g/m~2 for Shanyou 63 and from 0 to 24 g/m~2 for Wuyujing 3. The head rice percentage, peak viscosity, and values of breakdown decreased, whereas chalky percentage, chalkiness, setback values were increased, when the amount of N application was from 16 to 40g/m~2 for Shanyou 63 and from 24 to 40 g/m~2 for Wuyujing 3. The results indicate that the amount of N at 160 kg/hm~2 and 240 kg/hm~2 could be as an index of N application for Shanyou 63 and Wuyujing 3, respectively, in the production for the good quality of rice. 2.Under the pot experiments, soil water potentials, ranged from 0 to -60 kPa, had no significant effect on brown rice percentage, milled rice percentage, kernel length/kernel width, amylose content, and protein content. There was no significant difference in the head rice percentage between treatments of the keeping flooded (control) and soil water potentials at -15 and -30 kPa for Shanyou 63 or at -15 kPa for Wuyujing 3. The head rice percentage, gel consistency, and alkali spreading values significantly decreased when soil water potentials at -45 and -60 kPa for Shanyou 63 or at -30, -45, and -60 kPa for Wuyujing 3. The chalky grain percentage, chalkiness, and setback values significantly decreased, while peak viscosity and values of breakdown were significantly increased, when soil water potentials at -15 and -30 kPa for Shanyou 63 or at -15 kPa for Wuyujing 3. The chalky grain percentage, chalkiness, and setback values were significantly grater, whereas peak viscosity and values of breakdown were significantly smaller, than those of the control when soil water potential at -45 and -60 kPa for both cultivars. The results suggest that soil water potential at -15 ~ -30 kPa and -15 kPa could be as low-limit indexes for Shanyou 63 and Wuyujing 3, respectively, in water-saving irrigation during the grain filling period of rice.3. The coupling effects of soil moistures and N levels on rice quality were studied A tank experiment was conducted. Under all the N levels (grain fertilizer at the rate of 0, 4.5, and 9.0 g N/m~2), the brown rice percentage, milled rice percentage and head rice percentage were the greatest, while chalky grain percentage and chalkiness were the lowest, for the moderate soil-drying treatment (soil water potential at -25 kPa). At the low level of N (0 g/m~2), the severe soil-drying treatment (soil water potential at -50 kPa) significantly degraded the milling quality, appearance quality, and eating quality. At the mid (4.5 g/m~2) and high (9.0 g/m~2) N levels, the differences in milling quality, appearance quality, and eating quality between the severe soil-drying and the keeping flooded wee not significant, or those in the former were benter than those in the latter. It could be concluded that the ineraction between soil moisture and N levels affects rice qualities, and that soil water potential at -25 kPa during grain filling and the amount of N at 45 kg/hm~2 as the grain fertilizer benefit the formation of good quality.