Evaluation Loss And Optimization Management Of Water And Nitrogen In Greenhouse Cucumber Field Based On WHCNS_Veg Model

Greenhouse vegetable productions mainly are peasant household as production units,lacking scientific water and fertilizer management techniques,resulting in excessive water and fertilizer input,which has caused the problem of excessive levels of nitrate in groundwater.which poses a serious threat to drinking water safety and human health.Therefore,it is desperately need for Scientific management of water and nitrogen in greenhouse vegetables.This study used a combination of optimized fertilization experiment and a soil-crop system model.The optimized fertilization experiment of cucumber was carried out in the Daxing District with high degree of intensive agriculture,and four treatments of farmers’practice and optimized fertilization were set.The data of yield,nutrient uptake and nitrogen leaching were collected during the growth period.The WHCNS_Veg（soil-vegetable system Water Heat Carbon Nitrogen Simulator）model was calibrated and verified using experimental measurements.Then,the effects of different irrigation amounts and nitrogen application rates on soil water and nitrogen fate and utilization efficiency of greenhouse cucumber fields were simulated and quantitatively analyzed.Considering the three objectives of the agronomic effect,environmental effect and the value of cost ratio,the osculating value method was used to comprehensively evaluate the optimal water and nitrogen management for cucumber in different growing seasons,which provided a technical reference for the sustainable development of greenhouse vegetable agriculture.The main conclusions of this study were as follows:1.The WHCNS_Veg model is accurate for simulating the water and nitrogen fate and crop growth of the greenhouse cucumber soil-crop system,and is a scientific and effective method for quantitative evaluation of water and nitrogen management.2.The result of optimized fertilization experiment showed that the nitrogen leaching decreased with the reducing of nitrogen application rate.Nitrogen leaching in spring-summer and autumn-winter growing seasons were 51.19²63.29 kg·hm^-2 and 42.24¹43.07 kg·hm^-2,respectively;the nitrogen leaching ratio were 10.62%²8.12%and 13.58%²0.12%,respectively.Compared with farmers’practice（FP）,the nitrogen leaching of the optimized yield fertilization treatment（OPT-3）in spring-summer and autumn-winter seasons were reduced by 80.56%and 70.48%,respectively.But the nitrogen leaching and leaching ratio were still high.The main reason is the nitrogen leaching caused by excessive irrigation resulting in high water loss.3.The ratio of water loss of FP treatment in spring-summer and autumn-winter seasons were 42.09%and 45.91%,respectively.The irrigation water amounts of best management practice（BMP）were399.7mm and 250.0mm,and the water loss ratio is 13.02%and 10.94%,respectively.Compared with FP,43.34%and 50.21%water resources were saved and water loss decreased by 82.47%and 88.14%,respectively,and irrigation water use efficiency（IWUE）was 1.73 and 1.99 times of FP,respectively.Therefore,optimizing irrigation is an effective way to improve irrigation water use efficiency and reduce water loss.4.The nitrogen application rate of BMP in the spring-summer and autumn-winter seasons were456.3 and 252.0 kg·hm^-2,respectively,which was 55.53%and 63.56%lower than that of FP treatment.The nitrogen leaching amount was 6.47 and 2.78 kg·hm^-2 and nitrogen leaching ratio were 1.37%and1.06%,respectively.Compared with FP,nitrogen leaching decreased by 97.54%and 98.06%,respectively,and nitrogen surplus decreased by 75.84%and 71.63%,respectively.Nitrogen use efficiency（NUE）was 1.92 and 1.59 times of FP,respectively.Nitrogen leaching was reduced by 87.36%and 93.42%,respectively,compared to OPT-3 treatment.Based on the principle of nitrogen balance in soil,the nitrogen application rate of BMP in spring-summer and autumn-winter seasons were 63.91 and40.76 kg·hm^-2,respectively.5.The key periods of water loss and nitrogen leaching in greenhouse cucumber in spring-summer season was:seedling stage,early melon stage,last melon stage;and autumn-winter season was:seedling stage and last melon stage.This study verified the accuracy of the simulation effect of WHCNS Veg model,explored the key period and influencing factors of water loss and nitrogen leaching of greenhouse cucumber in spring-summer and autumn-winter seasons,and determined the optimal water and nitrogen management measures of greenhouse cucumber with efficient utilization of water and nitrogen and friendly environment.