Evaluating Water And Nitrogen Loss In Greenhouse And Optimize Water And Nitrogen Management In Greenhouse Cucumber Field In Beijing Region

Beijing has about 62000 ha cultivation area of vegetables, and the conventional irrigation and nitrogen fertilizer practices are employed on the over half of the total of vegetable cultivation area. The objective of this study was to identify optimal water and N fertilizer inputs for a cucumber field in Beijing region using the calibrated EU-Rotate_N model combined with the osculating value method. The measured data used to calibrate and validate the model were collected from an experiment with four water and N fertilizer treatments, including furrow irrigation+conventional fertilizer (FP), drip irrigation+conventional fertilizer (FPD), furrow irrigation+optimal fertilizer (OPT), and drip irrigation+optimal fertilizer (OPTD). The main results of our study were as follows:(1) Based on calibration and validation of EU-Rotate_N model with field data, the values of RMSE, E, d,correlation coefficient and PBLAS between simulated and measured soil water content, NO3-N concentration, cucumber yield indicated EU-Rotate_N model had good performances on simulating water and nitrogen dynamics and crop growth in this study. Therefore, the model could be used to analyse the fates of water and nitrogen in three vegetable cropping systems under different irrigation and fertilizer management.(2) Compared with FP treatment, the FPD, OPT, and OPTD treatments don't significantly affect the cucumber yield. The simulation results indicate that the water drainage and nitrate leaching are highly coupled, and they usually occur after the irrigation and fertilization events. Compared with furrow irrigation, the amount of water drainage reduces by 74-77% under drip irrigation. As a consequence, the water use efficiency (WUE) increases 21-29%.Whereas, optimizing nitrogen fertilizer rates has no significant effect on water drainage and WUE under both drip and furrow treatments. Moreover, compared with furrow irrigation, the amount of nitrate leaching reduces by 69-82% under drip irrigation. Optimizing nitrogen fertilizer input also significantly decreases the amount of nitrate leaching by 12-49%. However, lager amount of nitrogen is left in the 0-90 cm soil profile under drip irrigation. The amount of residual nitrogen under drip irrigation is 5 times as much as that under furrow irrigation. Optimizing irrigation and nitrogen fertilizer inputs result in the increases in the nitrogen use efficiency (NUE) by 42-47%and 13-21%, respectively. Among of four irrigation and nitrogen fertilizer treatments, the values of WUE and NUE are the highest under the OPTD treatment, and are 48.4 kg m-3 and 185 kg kg-1, respectively.(3) We simulated the responses of the cucumber characteristics and the balances of soil water and nitrogen to 240 water and fertilizer applications scenarios under furrow and drip irrigation, respectively, the simulated results indicated that cucumber yield increased to the maximum value as the inputs of water and nitrogen reached approximately 277 mm and 310 kg N ha-1. Using the Agronomic factor, Value to cost ratio, and environment factor as the assessment indicators, the results of the osculating value method indicated that 300 mm of irrigation with 300 kg N ha-1 and 250 mm of irrigation with 300 kg N ha-1 were the best management practices (BMPs) for the greenhouse cucumber in this study region under the furrow and drip irrigation, respectively.