| Abstract:Rice is one of the main food crop, and more than half of the world population depends on rice as the staple food, so high and stable yield of rice has a very important significance to safeguard world food security. Panicle fertilizer was not taken seriously, and a serious shortage of nitrogenous fertilizer in the crop late growth stage is the common problems in agricultural production Which may lead late leaves of rice is easy to senescence, and even premature aging, and it could serious impact on the rice yield potential, or even result in reduction of yield. In this study,27of the main indica cultivars in Henan south rice area and conventional Japonica cultivar YunongJing6in the rice area along the Yellow River Valley as experimental material, and field experiments were taken at the science and Technology Park of Henan Agricultural University from2010to2011. The SPAD value of leaves on different position were used for cluster analysis, and the leaves senescence physiological and biochemical mechanism under the nitrogen starvation in late stages and technology of delaying leaves senescence were studied, in order to provide the theoretical basis for delaying the rice leaves senescence and improving the traditional cultivation mode, and also to provide more rational and effective cultivation and management measures for the rice high and stable yield. The results are as follows:1. Leaf senescence genotype screening and its relation mechanism:The rice plant growing status is composed of leaves physiological characteristics, so the leaves differ in their contributions to the growth of the whole plant, its grain yield and quality. As the SPAD value is the available indicator of the leaf status in rice, and the SPAD Change Rates can be indicated the senescence rates of the leaves. The SPAD value after flowering was determined in a field experiment on different positions of27indica rice cultivars, and the SPAD value change rates (SCR)was also calculated, and the correlations among SPAD value, SCR,and yield,inferior grain plumeness, taste quality were also analysed. the results showed that:ⅰ. SPAD value, SCR, inferior grain plumpness, rice yield and eating quality among different rice cultivars in the same field nitrogen deficiency conditions in the various periods showed differences, but their change tendency showed consistency. ⅱ. A dendrogram established based on Hierarchical culuster analysis could divid27indica rice cultivars into6groups among which there were somelesf sencescence ralations. ⅲ Inferior grain plumpness, yield, taste quality and SPAD value at the middle grain-filling stage showed a negative correlation, but the correlation became positive at the later grain-filling stage. that indicated the higher SPAD value of cultivars in the whole grain-filling stage were not an advantage for final rice quality traits。Characteristics of leaf senescence and grain filling dynamics were investigated in Rice cultivars Fengliangyou4, Lufeng20under the nitrogen deficiency condition in the grain-filling period. The results showed that, leaf senescence of Fengliangyou4and Lufeng20showed consistent overall trend, but there were significant differences in senescence process. Compared with Fengliangyou4, the SOD, CAT activity of functional leaves of Lufeng20decreased more slowly which showed longer photosynthesis function duration, and particularly the grain-filling process was significantly promoted. In rice production, rice cultivars with slower leaf senescence rate, longer function period with appropriate cultivation and management techniques used to improve the leaf senescence process can be achieved to promote rice grain filling and improve rice yield.2. The effects of deep tillage and panicle fertilization on rice root activity, grain filling dynamics and yield were investigated. A field experiment was carried out in a randomized complete block design with four treatments at top forth leaf stage. The treatments were broadcast-application without deep tillage, broadcast-application with deep tillage, broadcast-application with deep tillage, furrowing and ridging, and deep-application with deep tillage. The results showed that, different treatments of deep tillage and panicle fertilization significantly improved activities of soil urease, invertase, phosphatase, catalase and dehydrogenase; different treatments of deep tillage and panicle fertilization increased root biomass and root/shoot ratio in the grain filling stage; different treatments of deep tillage and panicle fertilization significantly increased the bleeding intensity at the basal internode and neck-panicle node; different treatments of deep tillage and panicle fertilization increased chlorophyll content and soluble-protein content, promoted SOD, CAT activity, reduced POD activity and MDA content, raised leaf chlorophyll fluorescence parameters Fo、 Fv/Fm、PSII、qP、ETR and decreased qNP, briefly effectively delayed the leaf senescence of grain filling stage; different treatments of deep tillage and panicle fertilization superior grain and inferior grain weight, the initial potential, relative starting potential maximum grain-filling rate and the average filling rate, maximum grain filling rate and time (inflection point) in advance, to improve grain filling; different treatments of deep tillage and panicle fertilization reduced the effective panicles and seed setting rate, but also increased grain number, grain weight and grain plumpness, thereby increased the Effective yield and theoretical yield; different treatments of deep tillage and panicle fertilization improved milling quality, appearance quality and eating quality. At the middle growth stage, deep tillage could increase soil enzyme activities and the vigor of root and sink, delay leaf senescence, refine grain-filling process, and then enhance grain yield improve rice quality in sandy loam soil. Deep-application with deep tillage showed the greatest positive effect, followed by broadcast-application with deep tillage, furrowing and ridging, and broadcast-application with deep tillage. |
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