Modeling nitrogen transport and leaching process in a greenhouse vegetable field

Nitrogen (N) leaching is caused by the mismanagement of water and fertilizer in greenhouse vegetable fields. Understanding N movement and leaching process is important for achieving high crop yields at low environmental costs. A field experiment was conducted for a greenhouse cucumber–tomato rotation system in the suburbs of Beijing, China. The DeNitrification-DeComposition (DNDC) model was used to quantitatively evaluate the soil N transport and leaching loss in the facility vegetable field after considering factors obtained from field experiments, such as soil temperature, humidity, and nitrate nitrogen (NO₃^--N) content. Conventional practices were selected as the baseline scenario, and the modeled scenarios, such as changes in soil properties, irrigation, and N application, were set according to the baseline. The results showed that the DNDC model can better simulate the vegetable yield, 5 cm soil temperature, 0–20 cm soil water-filled pore space, and NO₃^--N migration process, indicating that it is an effective tool for simulating and evaluating N transport and leaching in vegetable field soil. The modeling scenarios showed that the accumulation of NO₃^--N in the 0–60 cm soil was primarily affected by the irrigation amount and N application; soil pH and organic carbon were also important factors affecting NO₃^--N migration. Increasing irrigation amount significantly accelerated the downward movement of NO₃^--N, and increasing N application promoted the accumulation of NO₃^--N at the surface and a depth of 20 cm. Increasing soil pH lessened NO₃^--N surface accumulation; and to a certain extent, increasing soil organic carbon delayed the downward movement of NO₃^--N.Controlling water and fertilizer was the most effective method for mitigating N leaching. Compared with conventional measures, reducing irrigation and N application simultaneously by 20% significantly reduced NO₃^--N leaching by 59.04%. Changing irrigation method and increasing soil organic carbon content by 20% (to save water and fertilizer) further reduced NO₃^--N leaching by 69.04%. The DNDC model is a useful method for evaluating and controlling NO₃^--N leaching in vegetable fields. Changing management practices, such as N and water amounts as the soil quality improves, may be an effective way to reduce N leaching in vegetable fields.