Effects Of Soil Moisture And Nitrogen Nutrient On Grain Yield And Quality Of Rice And Their Physiological Mechanism

Soil moisture and nitrogen (N) nutrient are the principal factors affecting rice production. Elucidation of their influences and coupling effects on grain yield of rice (Oryza saliva L.) would have great significance in conducting the cultivation for high yielding, good quality and high efficiency. In this study, typical Japonica and Indica rice cultivars, currently planted in local rice production in Jiangsu, were used as materials, and water culture, pot and field experiments were conducted. Treatments of different soil water potentials (ψsoil) and N levels at different growth stages (seedling stage, whole growing period, early and mid growing period, and grain-filling period) were designed for each experiment. Effects of soil moisture and N levels on the grain yield, quality, and their physiological mechanism were investigated. The main results are as follows:1. There were visible interactions or coupling effects between soil moisture and N levels on grain yield of rice. The strength of the effects depended on the degree of soil water deficit, N levels, and growing stages. Mathematical models were established to analyze the coupling effects of N levels (X|) and Ψsoil (X2) on the grain yield (Y) when soil water deficit imposedduring the whole growing period (transplanting-maturity), early and mid growing period (transplanting-heading) and grain-filling period (heading-maturity).Y = 41.04 + 10.67X, + 0.0034X2 -0.99 X2, -0.005X22 - 0.018 X,X2 (whole growingperiod)Y = 43.13 + 8.98X, + 0.0223X2 -0.819 X2! -0.004X22 - 0.0124 X,X2 (early and midgrowing period)Y = 88.36 + 15.42Xi + 0.504X2 -2.89 X2, -0.014X22 - 0.0241 X|X2 (grain-fillingperiod)The optimum amount of N applied or the optimum ^oii could be obtained based on these models when soil moisture or amount of N applied was kept at a certain level. The models show that the optimum amount of N applied would not be increased, instead, it should be reduced, with the decrease of Ψsoil.2. The effects of moderate water deficit (Ψsoil at -20 kPa) and medium water deficit (Ψsoil at -40kPa) on milling quality of rice were insignificant when the water deficit imposed during the whole growing period or during the early and mid growing period. The milling quality was improved when a moderate water deficit ('Psoii ^ -25kPa) was imposed during the grain-filling period. The effect of water deficit on head-milled rice was positive for Wuyujing 3, but negative for Shanyou 63.When the treatments of soil water deficits and N levels were conducted during the whole growing period or during early and mid growing period, the percentage of chalky grains was LN (low amount of N)