A Model For Management Of Nitrogen Concentration In The Nutrient Solution For Soilless Cultivated Cucumber Crops In Greenhouse

Cucumber is one of the most popular crops cultivated in greenhouse in the world. Nitrogen is the important nutrient affecting dry matter production,partitioning and yield formation of plants.The aim of this study is to quantitatively investigate the demand of nitrogen(N) of greenhouse cucumber.Experiments with different planting dates and levels of nitrogen application rate after anthesis for greenhouse fruit cucumber(Cucumis Sativus.'Deltastar') were conducted in a multi-span PVC greenhouse in Shanghai during 2005～2006.The integrated photo-thermal index,the average product of thermal effectiveness and PAR above canopy(ATEP),was used to describe the optimal leaf nitrogen concentration of greenhouse cucumber under different radiation and temperature conditions.Based on these quantitative relationships,a management model of nitrogen concentration of the nutrient solution was developed.Another experiment was held in order to test and validate the model for management of nitrogen concentration in the nutrient solution for soilless cultivated cucumber crops in greenhouse.The results show that the nitrogen concentration suggested by the model results in higher nitrogen use efficiency while keeping the yield as high as the conventional nitrogen concentration. Therefore,the model developed in this study can be used for precision management of nitrogen for greenhouse cucumber crop production.(1) The model for management of nitrogen concentration in the nutrient solution for soilless cultivated cucumber crops in greenhouse.The seasonal time course of leaf nitrogen concentration and its relation to the leaf net photosynthesis rate and yield were analyzed. Then,the optimal leaf nitrogen concentration for soilless cultivated cucumber crop in greenhouse in different seasons was determined.Leaf net photosynthesis rate and yield of cucumber were found to be increased exponentially with the leaf nitrogen concentration at the middle fruit harvest stage.The relationship between the leaf nitrogen concentration at the middle fruit harvest stage and the nitrogen concentration of the nutrient solution was then quantified.Based on these quantitative relationships,a management model of nitrogen concentration of the nutrient solution was developed.The results show that the leaf nitrogen concentration at the middle fruit harvest stage was used as an index for nitrogen management for cucumber crop in greenhouse.The leaf nitrogen concentration at middle fruit harvest stage should higher than 3.2%,3.5%,respectively,for the Spring-Summer season and the Autumn-Winter season and the corresponding nitrogen concentration of the nutrient solution were at least 90 mg·L^-1 and 65 mg·L^-1 respectively.(2) Test and validate the model.Experiments with three levels(model suggested level 160 mg·L^-1,conventional level 80 mg·L^-1 and low nitrogen level 40 mg·L^-1) of nitrogen application rate were conducted in a greenhouse in Shanghai during 2006.The seasonal time course of leaf net photosynthesis rate,shoot biomass,yield and nitrogen use efficiency of the cucumber crops with the three levels of nitrogen application rate were analyzed.The results show that the cucumber crops with nitrogen application rate of model suggested level(80 mg·L^-1) and that of conventional level(160 mg·L^-1) did not have significant differences in leaf net photosynthesis rate,shoot biomass production and yield.The nitrogen use efficiency of the cucumber crop with nitrogen application rate of model suggested level was 18.9%higher than that of conventional level.The nitrogen concentration suggested by the model results in higher nitrogen use efficiency while keeping the yield as high as the conventional nitrogen concentration.The model reduce the waste of nitrogen and protect the environment,hence,can be used for optimization nitrogen management for greenhouse fruit cucumber production.