Identifying optimal water and nitrogen inputs for high efficiency and low environment impacts of a greenhouse summer cucumber with a model method

High-input of water and nitrogen (N) fertilizers in intensive greenhouse vegetable production regions in China has successfully increased crop productivity in the past decades, but at a significant environmental cost and resource consumption. It is essential to choose best management practice (BMP) to meet multiple goals, such as keeping greenhouse vegetable yield stable, improving nitrogen use efficiency (NUE), and reducing the nitrogen pollution issue. However, the bottleneck is the capacity of predicting the simultaneous effects of different management practice scenarios on multiple goals and choosing BMP among scenarios. The object of this study was to identify BMP of water and N fertilizer for greenhouse summer cucumber in North China Plain using calibrated and validated EU-Rotate_N model. The data used to calibrate and validate the model were collected from a typical greenhouse summer cucumber field with four different water and N fertilizer treatments within the target domain region. A total of 240 varied scenarios of water use and fertilizer application were set up and then simulated by the model. An osculating value method was used to evaluate combinations of irrigation and fertilizer practices. Agronomic indices (yield, WUE and NUE), environmental indices (nitrate leaching and gaseous N loss), and economic index (value to cost ratio) were selected as the evaluation indices to identify the BMP. The results showed that cucumber yield increased to maximum value as water input reached to about 277 mm, then kept constant or even decreased under lower N fertilizer rates. Nitrogen started to lose as nitrate leaching when irrigation increased to 300-400 mm, and then nitrate leaching increased with irrigation increasing. The effects of water input on gaseous nitrogen loss were not significant. Regardless of N fertilizer rates, irrigating about 300 mm water can obtain the maximum NUE. Cucumber yield increased to maximum values as N fertilizer input reached to about 313 and 310 kg N ha−1 for furrow and drip irrigation, then was not affected by N fertilizer increase. The BMPs under furrow irrigation condition were to irrigate 300 mm with 300 kg N ha-1 and 250 mm with 300 kg N ha-1 under drip irrigation condition for greenhouse cucumber in the study area, respectively. Adopting the current BMPs, the applied nitrogen and irrigation water were at about 55 and 40% lower rates, respectively, than the current conventional use. Our study indicated that the EU-Rotate_N model combined with Osculating value method can be helpful to assess multi-goal effects of management alternatives and identify BMP.