| Nitrogen is an important factor of restricting the yield of cassava, it has certain effect on plant growth and physiological and biochemical indicators. Because of the tapioca growers are blind to nitrogen fertilization, lack of unified standards on applying content and application time. It made the nitrogen fertilizer utilization was low, production was not guaranteed. This study investigates the effects of nitrogen nutrition characteristics and yield formation of Cassava in field trials under four nitrogen levels(0,120,240, 360kg/hm2). We made sure the optimal amount of nitrogen fertilizer and fertilization time and fertilizer proportion in each time period of cassava, to provide theoretical and practical foundation of fast-growing and high-yield of cassava. On this basis, the low nitrogen treatment was studied by pot experiment further (normal level of 0%,0%,40%,60%,80%, 60%) of the cassava seedling growth and development, nutrient accumulation characteristics and the influence of the physiological and biochemical indexes, and analyzed the relationship between the physiological and biochemical indexes and the applied amount of nitrogen fertilizer, screened nitrogen nutrition diagnosis index of cassava in the different stages of seedling, for early monitoring of plant nitrogen nutrition status, and provide theoretical and production on the basis of reasonable application of nitrogen fertilizer. The results of the study were as follows.1. The influence of nitrogen nutrition characteristics, yield and quality in different nitrogen levels under field conditions.With the increase of nitrogen application rate, the nitrogen content, nitrogen accumulation and cassava organs absorption intensity increased as well, and effectively promoted the whole plant dry matter formation. When the N application rate was less than 240 kg/hm2, with the increase of N application, cassava root dry matter accumulation, fresh cassava yield and starch yield were significantly improved, and the N application rate of 240 kg/hm2 achieved the maximum value. N application rate was 360 kg/hm2, plant nitrogen mainly allocated to the stem leaf spot, causing moderate growth, went against with root formation, made its root dry matter accumulation, fresh cassava yield, starch yield were significantly less than 240 kg/hm2 level. In conclusion, the optimum nitrogen application amount was 240kg/hm2.With cassava growth, nitrogen absorption intensity and absorption ratio showed a trend of rise before reducing, highest in stem bifurcation stage, when N application levels for 240 kg/hm2, and the optimum proportion of nitrogen application was 1:1.71:1.33:0.73:0.57 at seedling stage, stem bifurcation stage, root tuber formation stage, first expanding root tuber growth stage and middle expanding root tuber growth stage, respectively. Nitrogen fertilization should concentrate on seedling stage, stem bifurcation stage and root tuber formation stage.2. The adaptive response characteristics of nitrogen deficiency under the condition of potted plant and screened nitrogen nutrition diagnosis index of preliminaryExperimental results showed that, with the increase of N application, cassava plant height, stem diameter, root length, fresh weight per plant, surface area and volume increase, NPK nutrients absorption, and glutamine synthetase activity of nitrate reductase and soluble sugar content increased, superoxide dismutase (SOD), peroxidase (POD) and catalase activity (CAT)increased, malonaldehyde (MDA) content decreased.Under the condition of low nitrogen, increased the application of nitrogen fertilization promoted the cassava agronomic traits, root growth, prompted the absorption of nutrients, improved the ability of carbon and nitrogen metabolism, and strengthened the resistance in seedling stage, stem bifurcation stage and root tuber formation stage.Under the condition of low nitrogen, nitrate reductase, glutamine synthetase activity can be used as early nitrogen nutrition diagnosis indicators,20-100 days after fertilization, cassava leaf nitrate reductase activity and nitrogen.content were very significant positive correlation, the critical value in 20,40,60,80,100 days were 12.089,8.570,22.239, 16.375,12.119 respectively; glutamine synthetase activity in 60,100 days after fertilization and were very significant positive correlation between N application rate, nitrogen deficiency critical value were 0.333,0.168, respectively. |
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