Study On The Effects Of Different N Application Modes On The Yield Of Ratoon Rice

Ratoon rice is reharvested a single season rice which uses dormancy bud to sprout and grow to produce effective panicles at rice stake after the first crop was harvested with the aid of a certain cultivation management. Ratoon rice is one of light and simple cultivation techniques with saving labour and cost as well as looking for without decreasing yield and benefit, aiming at further raising crop yield and farmers income. In this study, hybrid rice 'combination II you hang 2'was employed as experiment materials. Dry matter accumulation and translocation dynamics as well as effect on yield formation and its physioecological mechanism, including properties of rhizosphere microbes in ratoon rice under the conditions of different nitrogen application modes were researched. The main results were summarized as follows:1. To study dry matter accumulation and translocation dynamics as well as the effects on yield formation in ratoon rice under the conditions of different nitrogen application modes. The analysis indicated that properly decreasing the proportion of N supplies in the early growth stage and increasing the proportion of N supplies in the middle and late growth stages have benefit to the increased production, which was attributed to the decreased ineffective tillers , resulting in a relatively suitable population withhealthy individual plants in the middle and late growth stages. Moreover, it was also found that nitrogen fertilizer given in the middle and late growth stage of rice appeared to be benefit with the growth of individual plants, and make net assimilation rate (NAR) and crop growth rate (CGR) significantly enhanced in the first crop for ratoon rice. This in turn led to increased net dry matter accumulation. Furthermore, spikelet number per m~2 and spikelet number per panicle as well as sink sizes were all significantly increased by properly increasing the proportion of N supplies in the middle and late growth stage. As a result, these factors engendered large sink size and plentiful source and made the yield of the first crop significantly enhanced. But, to dry matter accumulation and the yield of the ratoon crop, the effect is not significant.2. To study physiobiochemical mechanism in ratoon rice under the conditions of different nitrogen application modes. The investigation demonstrated that nitrate reductase(NR) activity of rice leaf ascended at the early stage,and reached to the peak at the booting stage of the first crop and then declined gradually, but ascended rapidly again at the full heading stage of ratoon rice, and rapidly turned to decline again at the ripening stage of ratoon rice. The result also showed that NR activity and chlorophyll contents as well as net photosynthetic rate of rice leaf in the middle and late growth stage of the first crop for ratoon rice were significantly improved as properly increasing the proportion of N supplies in the same stage. At the same time, the rate of phloem sap was also enhanced, especially at the booting stage of the first crop for ratoon rice. These in turn resulted in increased CGR and dry matter accumulation, which was considered the physiological basis to produce high grain yield.3. To study ecological effect of photosphere microbes in ratoon rice under the conditions of different nitrogen application modes,we detected the soil microbial flora and enzyme activity in the rhizosphere of the first crop. The results indicated that mutative trend of soil microbial metabolic biomass carbon and nitrogen, soil urease , acid phosphatase, soil microbial flora and the cultivated microbial physiological flora in different treatments of the first crop of ratoon rice were the same. Amount of bacteria, actinomycetes,ammonifier, nitric acid bacteria,aerobic azlotobacter and content of soil microbial metabolic biomass carbon and nitrogen slowly ascended after rice was transplanted , rose to peak at tillering in the first crop stage and then rapidly declined to the lowest at the booting stage of the first crop, then went up slowly again during rice growth after the booting stage. Activity of soil urease and acid phosphatase were gradually enhanced after rice transplanting, they were the highest at the booting stage of the first crop, then declined rapidly again during rice growth, and turned to be the lowest at ripening stage of the first crop. The behavior of fungi and denitrifier as well as desulphate reducer were quite different from bacteria and actinomycetes. Amount of fungi and denitrifier and desulphate reducer drop off after rice transplanting, and went down to the lowest at the booting stage of the first crop,then increased slowly again during rice growth.The result from this experiment also showed that properly increasing the proportion of N supplies in the middle and late growth stage had benefit to the growth of bacteria,actinomycetes,ammonifier,ntric acid bacteria and aerobic azlotobacter in the middle and late growth stage of the first crop,indirectly improved activity of soil urease and acid phosphatase. All of these built up a nicer nutrition surrounding and matter basis for rapid growth of the first crop.