| Nitrogen is one of the major nutrients that affect growth and yield of crops. Generally speaking, it is very difficult to grasp the difference of nitrogen nutrient in the field soil and change of nitrogen situation during crop growing season, when nitrogen fertilizer was applied. Therefore, Nitrogen is one of fertilizers that is the most difficulte to ensure the accurate rate in crop production. It depended on the accurate diagnosis of crop nitrogen level to regulate crop nitrogen nutrition and improve nitrogen use efficiency.Therefore, the diagnosis of nitrogen nutrition is always the main components of crop nutrition diagnosis .The field plot experiment and aquatic culture experiment were conducted in greenhouse to study the possibility of cucumber nitrogen nutrition diagnosis using leaf SPAD value and NRA as diagnosis index and the most suitable diagnosis time and leaf position by analysising the relationship between nitrogen rate, leaf SPAD, NRA and the cumulation and changes of nitrate nitrogen in crop.So that we can offer the guideline to diagnose cucumber nitrogen nutrition fastly in greenhouse.1. There was a significant relationship between SPAD values mensurated by chlorophyll meter and N fertilizer rate and cucumber yield and nitrate content, according to analyzed results in the cultivation conditions.Therefore, it could predict cucumber yield and the leaf nitrate content, and diagnosie nitrogen nutrition in cucumber.2.The results showed that the leaf SPAD value increased significantly with increasing of N rate, and it could be used as index for diagnosis of cucumber nitrogen nutrition. The best diagnose periods of nitrogen nutrition in cucumber were florescence and fruitin, the 3L's SPAD values at seedling stage and in florescence and the 7L's in early fruitin were more sensitive, they were suggested to be the best leaf position to diagnose the nitrogen nutrition Status of cucumber.3. The 3L's NRA at seedling stage and in florescence and the 7L's in early fruitin were more sensitive, they were suggested to be the best leaf position and period in cucumber nitrogen nutrition diagnosis. There were the common change of the leaf SPAD values,NRA and nitrate nitrogen in two periods and all increased significantly with increasing of N rate and opposition with soil active nitrogen. 4. The NRA critical values were 67.45 and54.3 ugNO2–g-1 FW·h-1 in florescence and early fruitin in cucumber nitrogen nutrition diagnose. The NRA critical values were different under same nitrogen levels at different stage.5. The content change of three essential elements in dry matter in whole plan growing periods is K>N>P. The proportion of NPK nutrient absorption were different at different growth stages of cucumber, P was the lowest, N and K were the higher, and K has great change at whole growing periods.6. The yield was the highest and the nitrate nitrogen content was lower in leaf and fruit with rate of 250 kg N /hm2. So, it should be the optimum nitrogen application rate in cucumber under this experiment condition. |
