| The present study was conducted to investigate the effects of different nitrogen application levels on the yield, sucrose contents, and physiological and biochemical characteristics of sugarcane to provide a references for high yield and high sugar sugarcane production. The experiment used a split-plot design in which three N levels (150,300 and 600kg/ha urea) were used in the main plots, and three varieties (GXB9, ROC22, GT11) were used in the sub-plots in 2013 (plant cane) and in 2014 (ratoon cane), respectively. The nitrogen metabolism-related enzyme activities and mainly active substance contents were measured, and the agronomic traits, and quality and yield of cane were investigated.The main results were as follows1. The activities of nitrate reductase (NR), glutamine synthetase (GS) and glutamate oxaloacetate transaminase (GOT), glutamate pyruvate transaminase (GPT) generally increased with the increase of nitrogen levels in three sugarcane varieties. The middle nitrogen treatment was significantly greater than the low nitrogen treatment, but no significant difference was found between the high nitrogen and middle nitrogen treatments.2. During sugarcane growth, the chlorophyll content showed a single peak curve which showed increase first and then decrease in all the varieties, and increase with the increase of nitrogen application level. The contents of free amino acid (AA) and soluble protein (SP) showed increasing with nitrogen level in a certain range, but the contents of soluble sugar (SS) and nitrate nitrogen (NN) showed decresing with nitrogen level. Attillering and booming stage, the contents of free amino acids and soluble protein respectively showed a significant and positive correlation with the activities of nitrate reductase and glutamate pyruvate transaminase.The content of free amino acids showed a significant and negative correlation with soluble sugar.3. The brix of juice, sucrose in cane, fiber in cane, sucrose in juice, gravity purity of juice were reduced with the increase of nitrogen level in the three sugarcane varieties, but the reducing sugar in juice is increased with the increase of nitrogen application. The sucrose content in cane of the three varieties showed GXB9> ROC22> GT11. For different crops, the brix and sugar content in cane showed slightly lower in ratoon than the plant cane.4. In a certain range, sugarcane stalk length was increased with the application amount of nitrogen, but it no longer increased over a certain extent, and it showed GXB9> ROC22> GT11. Stem diameter had no significant difference for different levels of nitrogen application and different varieties, but it was significantly greater in the ratoon cane than in the plant cane, In the ratoon crop, the single stalk weight showed the maximum for the middle level of nitrogen application; the millable stalks/ha showed the maximum at the middle nitrogen application level for GXB9 and GT11, but at the high level of nitrogen application for ROC22. The cane yield showed middle N> low N>high N for GXB9, high N> middle N> low N for ROC22, and middle N> high N> low N for GT11. Regression analysis showed that the cane yield of GXB9 would reach the maximum of 182.0t/ha when 360.5kg/ha nitrogen fertilizer were applied, and that of ROC22 reached the maximum of 179.3t/ha when the urea application rate is 430kg/ha. In the range 0 to 600kg/ha urea application rate, the cane yield of GT11 showed increasing with nitrogen application level.5. Based on the results of the present study, middle N level (300kg/ha urea) of nitrogen fertilizer might achieve the best comprehensive benefits for improving both cane and sugar production. |
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