Managing irrigation and fertilization for the sustainable cultivation of greenhouse vegetables

Nitrogen (N) leaching is an important factor that threatens groundwater safety in intensive greenhouse vegetable production regions. However, managing irrigation and fertilization to reduce nitrate leaching has rarely been carried out in long-term experiments. In this study, N leaching in two typical greenhouse vegetable systems (a cucumber-cucumber system in Shandong and a cucumber-tomato system in Ningxia) from 2008 to 2013 investigated should be studied using a lysimeter monitoring method. The total N fertilization rate was 0 to 2508 kg N ha(-1) which included three treatments: no fertilizer (CK: 0 kg N ha(-1)), conventional treatment (CON: Shandong 2508 kg N ha(-1) and Ningxia 2239 kg N ha(-1)) and reduced fertilizer application (RF: Shandong 2164 kg N ha(-1) and Ningxia 1716 kg N ha(-1)). The irrigation amount was 590-2919 mm year(-1) according to vegetable water demand. The results indicated that the annual total N leaching were 344.8 kg ha(-1) (192.3-508.3 kg ha(-1)) in Shandong and 170.7 kg ha(-1) (134.9-203.7 kg ha(-1)) in Ningxia for the CON treatments. Compared with CON treatment, RF significantly decreased ANLL, while simultaneously maintaining the yield and increasing the downward trend of the annual TN leaching factor (ANLF) year by year. Meanwhile, a concomitant annual cost reductions associated with the RF treatment estimated at $187 million USD for Shandong and $20 million USD for Ningxia. ANLL increased linearly with the N input (p < 0.05). More than half of ANLL came from fertilizer N (including chemical and manure fertilizer) under CON treatments, while more than half of ANLL came from soil and water N under RF treatments. The results indicated that mitigation measures for N leaching pollution from greenhouse vegetable fields should consider regulations on irrigation and fertilization.