Optimal drip fertigation management improves yield, quality, water and nitrogen use efficiency of greenhouse cucumber

Establishing reasonable water and fertilizer inputs is of great importance to improve crop yield and water and fertilizer use efficiency in greenhouses. This experiment was conducted in 2013 to investigate the effects of different levels of irrigation and nitrogen (N) fertilizer on the yield, fruit quality, and water and nitrogen use efficiency of cucumbers under fertigation systems in a greenhouse in China. The least square method and multiple regression analysis were used to select the largest single target and multi-objective optimum in this study. The treatments comprised three drip irrigation levels (with ET0 as the reference crop evapotranspiration, W1: 60% ET0; W2: 80% ET0 and W3: 100% ET0) and four N fertilizer levels (N0: 0 kg/ha; N1: 180 kg/ha; N2: 360 kg/ha and N3: 540 kg/ha). The results revealed that the single factors of irrigation and N had an extremely significant effect on the yield. The fruit yield increased with the amount of irrigation water and reached 55.9 t/ha and 51.6 t/ha with the use of N 540 kg/ha and 360 kg/ha, respectively. The yield of 49.6 t/ha, the highest water use efficiency (WUE) of 55.8 kg/m3 and vitamin C of 128.4 mg/kg were obtained from conditions involving medium irrigation levels (80% ET0) with the application of 360 kg/ha N. The highest soluble sugar content at 2.8% was achieved when the irrigation level was 60% ET0 and the application of N was 360 kg/ha. The nitrogen production efficiency (NPE) and partial factor productivity of nitrogen (PFPN) decreased with the increase in the nitrogen application rate. The highest NPE and PFPN of 263.4 kg/kg and 265.9 kg/kg were obtained from irrigation levels of 80% ET0 and 100% ET0, respectively. The yield response factor ky of the cucumbers was 0.94. Taking into account the yield, quality, and water and nitrogen use efficiency, the irrigation level of 80% ET0 with the nitrogen level of 360 kg/ha were the best fertigation strategy. Within a 90% confidence interval, it was concluded that when the irrigation interval was 124-151 mm and the nitrogen interval was 318-504 kg/ha, the yield, WUE, and Vitamin C reached ≥90% of their maximum values at the same time. The determination of this region is of great significance to the management of water and fertilizer in greenhouse cucumis sativus.