Crop Growth Model-Based Decision Support System For Greenhouse Cucumber Nitrogen Management

Nitrogen is an essential nutrient element which affects the crop growth and the yield and quality. The extensive management used in china greenhouse crop production leads not only to reduction of nitrogen utilization, but also to the environment problems such as the pollution of groundwater caused by the leaching of excessive nitrogen fertilizer. Optimizing the nitrogen management in greenhouse production is one of the most important measures to improve nitrogen utilization, ensure the yield and quality, and achieve the pollution-free production. As a powerful tool to optimize nitrogen management and decision-making in crop production, crop growth model is able to predict the crop growth and yield under various levels of nitrogen supply. Cucumber is one of the major cultivated crops in china. Combined with gathering annual meteorological data, crop information, cultivation management information, etc, the research validates the existed greenhouse cucumber growth simulation model through the experiment of various nitrogen treatments, sets up a systematic data-base, establishes nitrogen management and decision-making system of greenhouse cucumber based on the growth model by organic integration of date-base, greenhouse cucumber growth simulation model and optimized model of nutrient solution nitrogen management. Then experimental data obtained in different planting date and nitrogen concentration of nutrient solution are used to analysis the nitrogen management and decision-making system. The concrete results including:(1) Model validation:independent and complete experimental data acquired from the practice research of greenhouse cucumber'daiduoxing'under different nitrogen treatments (40,80,120,160mg·L-1) in Shanghai Academy of Agriculture Sciences Venlo-type greenhouse from the year 2007 to 2008 were used to validate the effects of existed nitrogen treatments on greenhouse cucumber growth simulation model and analysis the reliability and practicality. The results showed that the coefficient of determination (R2) and the relative error (RE) between the measured and simulated leaf area index (LAI), total dry weight, fruit dry weight and yield are 0.92,0.94,0.93,0.95 and 12.1%,13.1%,9.7%,9.1%, respectively, indicate preferable predictability and reliability of this model.(2) Decision model:combining the greenhouse cucumber growth simulation model with optimized nutrient solution nitrogen management model, a decision-making model of cucumber nitrogen management has been established. According to the greenhouse environment information and the user's presetting target harvesting time and target yield Y, the model calculates the suitable leaf nitrogen concentration NL and the corresponded nutrient solution concentration NC. The relationships among Y, NL, and NC can be derived:Y120=120×(Y/Tday)DW=Y120*DMC/HI/PIFN%=m*exp(-n/NC)*10HI=HImax×(1-exp(-c*(TEPab-13))) TEPab>13b=0.0095+(0.042-0.0095)×exp(-0.044×NL)c=0.025+(0.059-0.025)×exp(-0.058×NL)Where DW is total dry weight, Y120 is the accumulated yield in 120 days. Y, Tday, NC, N%, m, N,10 represent the target yield (kg·m-2), harvest days (day), nutrient solution concentration (mg·L-1), leaf nitrogen concentration (mg·g-1), theoretical maximum value of leaf nitrogen concentration in full fruit period under different planting date, the slope of negative exponential curve, and conversion factor, respectively. According to our research, the parameter m and n took value at 38,9.4 in spring-summer season respectively, and at 42, 11.3 in autumn-winter season respectively.; PIF is portioning index of fruit, HI is harvest index, and TEPab (MJ·m-2) is the accumulated product of thermal effectiveness and PAR during certain growth stage. NL, b, c, DMC represent leaf nitrogen concentration in full fruit period (mg·g-1), relative increasing rate of PIF, relative increasing rate of HI, and cucumber dry matter content (g·g-1).The case analysis of decision-making model focused on greenhouse cucumber production data obtained from different planting date and various nitrogen concentration treatments, indicated that in full fruit period the leaf nitrogen concentration increases along with the increase of the accumulated yield in 120 days. To attain the target yield that 7.2kg·m-2 in the spring-summer season and 6.5kg·m-2 in the autumn-winter season, the minimum leaf nitrogen concentration at least reached at 34 mg·g-1 and 3.2 mg·g-1 in full fruit period which required the nutrient solution concentration at 113 mg·L-1 and 82 mg·L-1, respectively.(3) System realization:based on windows XP as a platform, the system uses Microsoft Accesses to construct date-base and adopts VB to system programming. Its database includes greenhouse environment data, crop data, and cultivation management data, while its model base includes the model of simulating the effect of nitrogen on greenhouse cucumber growth, the model of nitrogen management decision-making model. The inputs of the system include the type of greenhouse, crop varieties data and cultivation management data. The outputs of the system contain leaf nitrogen concentration, the concentration and formula of nutrient solution. Base on the greenhouse environmental information and the suitable nitrogen scheme given by the target yield, the system can provide the decision support for the nitrogen optimal management of greenhouse cucumber production.