Effects Of Water-Nitrogen Interaction On Yield Formation And Characteristics Of Nitrogen Utilization In Rice And Its Physiological Basis

The water and fertilizer are two factors with mutual interaction and restriction in the process of rice growth and development. Elucidation of their influences and coupling effects on different irrigation regime and nitrogen fertilizer management, optimization water and nitrogen interaction management technology on grain yield and growing development of rice would have great significance in reducing irrigation water and fertilizer efficient utilization for high and stable yields. In this study, hybrid rice Gangyou 527 was used to investigate the effects of three irrigation regimes (submerged irrigation, W1; dry cultivation, W3; and damp irrigation before booting stage plus shallow irrigation at booting stage plus wetting-drying alternation irrigation from heading stage to mature stage, W2) and different nitrogen rate, and different nitrogen application on yield formation and characteristics of nitrogen utilization in rice and its physiological mechanism. The main results are as follows:1. Effects of water-nitrogen interaction on yield and yield componentsThe result indicated that the grain yield was influenced by different water-nitrogen treatment regimes in past years experiments, and there was an obvious interaction between irrigation regime and nitrogen management mode. The regime for highest yield was W2 and suitable nitrogen application amount (180 kg ha-1) in 2008. Under this condition, water- nitrogen interaction had significant positive effect on grain yield. Reasonable amount of nitrogen was established in 2009 through the experiment for previous one year. W2 irrigation regime and "Stable application at early stage, large application timely at middle stage" pattern of N3 nitrogen application regime (the ratio of base fertilizer to tillering fertilizer and to panicle fertilizer was 3:3:4, and split panicle fertilizer were applicated at 3.5 and 1.5 leaf age from top) gave full play to water-nitrogen interaction advantage, and was beneficial to absorb and utilize water and nitrogen fertilizer at different growth period of rice, and on the premise of a certain amount of effective panicle and seed-setting rate, this condition of W2 and N3 nitrogen application regime had significantly increased grain number per spike and 1000-kernel weight, then to promoted yield. Optimum amount of nitrogen was 180 kg ha-1 under submerged irrigation, and the ratio of postponing nitrogen application to the total amount of nitrogen was suitable for 40%-60%. However, the treatment of dry cultivation with the proper decrement of nitrogen application amount at 90-180 kg ha-1, nitrogen rate of panicle fertilizer should be properly reduced in nitrogen application, and the ratio of postponing nitrogen application to the total amount of nitrogen was suitable for 20%-40%, could ease the negative effect of water- nitrogen interaction.2. The effect of water-nitrogen interaction on rice population qualityThe result indicated that the rice population quality was also influenced by different water-nitrogen treatment regimes, and there was an obvious interaction between irrigation regime and nitrogen management mode on some index of population quality. W2 and suitable nitrogen application amount (180 kg ha-1) with N3 nitrogen application regime could control the number of rice tillering in time; improve the rate of tiller panicle; guarantee the rice of heading to reach the appropriate leaf area index (LAI) and grain-leaf ratio; reduce the inclination of the top three leaves suitably; increase leaf area ratio and group efficient light transmission rate; promote leaf photosynthesis of the lower population, and it would improve plant photosynthetic capacity of grain-filling stage and the accumulation of photosynthetic products.3. Relationship of activities of key enzymes involved in nitrogen metabolism with nitrogen utilization in rice under water-nitrogen interactionThe results showed that there was an obvious interaction between irrigation regime and nitrogen management mode on activities of key enzyme and nitrogen utilization. Compared with other irrigation treatments, the treatment W2 promoted the nitrogen uptake from tillering to heading, nitrogen dry matter production efficiency (NMPE) and nitrogen production efficiency (NPE). W2 and suitable nitrogen application amount (180 kg ha-1) in 2008, and W2 and suitable N3 application regime in 2009 enhanced activities of nitrogen metabolism enzymes, yield, and nitrogen use efficiency, being the best model in this paper referred as the water-nitrogen coupling management model. N4 nitrogen application regime (the ratio of base fertilizer to tillering fertilizer and to panicle fertilizer was 2:2:6, and split panicle fertilizer were applicated at 3.5 and 1.5 leaf age from top) and applying nitrogen 270 kg ha-1 resulted in negative effect of water-nitrogen interaction, slowing down the increase of activities of nitrate reductase (NR), glutamine synthetase (GS), and glutamate synthase (GOGAT), decreasing nitrogen agronomy efficiency (NAE), nitrogen recovery efficiency (NRE), and yield. Correlation analysis indicated that there existed significantly or highly significantly positive correlations of activities of nitrogen metabolism enzymes with indices of nitrogen uptake and utilization and yield, with different correlation coefficients of different growth stages. According to the conditions above, GS activity in function leaves might be a candidate indicator for nitrogen uptake and accumulation at different growth stages, and activities of NR, GS, GOGAT and endopeptidase (EP) in flag leaves at heading stage for rice yield and NMPE, NPE, NAE, NRE.4. Effects of water-nitrogen interaction on rice senescence physiology during grain-filling periodThe results showed that W2 and suitable nitrogen application amount (180 kg ha-1) in 2008, and W2 and suitable N3 application regime in 2009 gave full play to water-nitrogen interaction advantage. Compare with other treatments, this condition of W2 and the best nitrogen application regime in different water-nitrogen interaction experiments from the past years delayed the increase of reactive oxygen species and malondialdehyde (MDA), had high photosynthetic rate (Pn) and promoted the accumulation of soluble protein content, etc., and enhanced the superoxide (SOD), catalase (CAT) and peroxidase (POD) activities, consequently, promoted material accumulation and promote yield. Applying nitrogen (270 kg ha-1) and nitrogen rate of panicle fertilizer account for too large proportion (N4) would result in a negative effect of water-nitrogen interaction and influence the normal physiological function of rice during grain-filling period. In addition, there was significant correlation between the physiological index, in which significant positive correlations was observed between O2, H2O2 and MDA, and a significant negative correlation between them with antioxidant enzyme activities, Pn and soluble protein content. Furthermore, in the process of leave senescence, underground was closely related to aboveground, and root vigor had high significant positive correlation with antioxidant enzyme activities, Pn and soluble protein, but it had high significant negative correlation with O2, H2O2 and MDA.5. Effects of water-nitrogen interaction on rice material transport during grain-filling periodEffects of water-nitrogen interaction on rice material transport in stem-sheath also have a significantly or very significantly interaction effect from heading to maturity period. Under this condition, W2 and suitable nitrogen application amount (180 kg ha-1), and W2 and suitable N3 application regime enhanced activities of the rice roots to absorb water and nitrogen coordination, promoted the grain-filling stage of material transport, and corresponding with the best way of water-nitrogen logistics conclusion that was obtained anti-aging water-nitrogen control measures; while the other water-nitrogen treatment interaction advantage decreased or even generated negative effects. Correlation analysis indicated that there existed significantly or highly significantly positive correlations between the material transport in stem-sheath and nonstructural carbohydrate transformation(NSC), and between each of them and yield under water-nitrogen interaction from heading to maturity period. According to water-nitrogen interaction effects can be showed that applying nitrogen (270 kg ha-1), W3 treatment and nitrogen rate of panicle fertilizer account for too large proportion (N4) would result in a negative effect of water-nitrogen interaction and influence the normal physiological function of rice during grain-filling period, meanwhile, material transport and grain filling rate were decreased, and then that caused rice yield reduction6. Correlations of N, P and K absorption characteristics and its relationship with grain yield under water-nitrogen interactionThe results showed that there was an obvious interaction between irrigation regime and nitrogen management mode on N, P and K absorption, transfer and distribution. Correlation analysis indicated that there existed significantly or highly significantly positive correlations between the amounts of N, P and K absorption, transfer, distribution, and between each of them and yield under water-nitrogen interaction at the mainly growth stages, and there existed highly significantly positive correlations between yield and the accumulations of N, P before heading stage and the amount of K absorption at tillering stage under water-nitrogen rate interaction, however, there existed highly significantly positive correlations between yield and the accumulations of N still at heading stage and the amount of P and K absorption relative delay of the growth stage at the experiment of water-nitrogen rate interaction under water-nitrogen application interaction. But N4 nitrogen application regime, applying nitrogen 270 kg ha-1 and W3 treatment would result in N accumulation too high or too low, which would aggravate negative effect of translocation conversion rate of vegetative organ.