Characteristics Of Nitrogen Utilization And Nitrogen Diagnosis In Sweet Potato

In this study, we investigated the influence of different applying nitrogen rates on growthc、 yield and quality of sweet potato through sweet potato field experiment. Meanwhile we also investigate influence of different applying nitrogen rates on accumulation uptakes, accumulations and allocation of nitrogen.nitrogen physiological characteristics. Indexes and model of nitrogen diagnosis were established and verified.The main results were shown as followings:According to the fertilization status we can see that, nitrogen can greatly improve the leaf area, the content of dry matter, photosynthesis characteristic,the yield and the quality of sweet potato. The average tuber yield,yield and commodity potato rate increased with the increase of nitrogen rate when the nitrogen rate was less than300kg·hm-2, they were decreased by higher nitrogen application. The soluble protein content and vc content increase with the increase of nitrogen rate, but the starch protein and soluble sugar content decreased.Through the correlation equation we can conclude that the optimal nitrogen application of two cultivars were291kg/hm2and281kg/hm2, The diurnal Variation of the sweet potato shows that the best survey time is AM9:00～11:00due to great change of photosynthesis parameter in else time.The absorption and accumulates of nitrogen decreased after increased with time in the growth period. Highest uptake rate emerged in tuber bulking stage of the two cultivars. Maximal value of the absorption accordingly emerged in the accumulation stage of the starch. The absorption and accumulates of nitrogen increased with the increase of nitrogen rate, and this tendency was not obviously in seedling stage, but the difference gradually became significant in the late growth stage. Production value increased with the increase of nitrogen rate when the nitrogen was less than300kg·hm-2, and they were decreased by higher nitrogen application; But nitrogenous fertilizers efficiency decreased after increased with the increase of nitrogen rate, and nitrogenous fertilizers efficiency reach its maximum when the nitrogen is300kg·hm-2. Agronomic efficiency (AE) and Physiological efficiency (PE) increased with the increase of nitrogen rate when the nitrogen was less than300kg·hm-2, they were decreased by higher nitrogen application. While the recovery efficiency (RE) and Partial factor productivity of applied N (PEP) decreased with the increase of nitrogen rate.The results showed that the SPAD readings measured by ethanol-acetone method shows an significant exponential relationship with chlorophyll content. With the increase of nitrogen rate, the SPAD readings of the forth leaf (form the top of shoot) shows an linear correlation with N applying rate, soil Nmin, total N of shoot and leaf and yield.So the SPAD readings can be indexes of nitrogen diagnosis for the sweet potato in tuber bulking stage. According to the relationship of SPAD readings, yield and N applying rate, regression equation were established:"Fenpibai" y=0.00001x2+0.012x+41.606"Zipihuang" y=0.00001x2+0.019x+43.636For the "Fenpibai" and "Zipihuang", the optimal values in tuber stage bulking were45.1and49.8respectively, and the critical values were44.6and48.7respectively.