Effects of intercropping and nitrogen application on nitrate present in the profile of an Orthic Anthrosol in Northwest China

Accumulation of nitrate in soil increases the risk of nitrate leaching and hence ground-water nitrate pollution. The impact of intercropping on nitrate accumulation in soil has been little studied in China. This field study integrated wheat (Triticum aestivum)/maize (Zea mays) and maize/faba bean (Vicia faba) intercropping systems to assess effects of intercropping on nitrate accumulation in the profile of an alkaline soil under various application rates of N and P fertilizers in 2000. The study was conducted in Gansu Province, China. Grain yields of wheat were significantly enhanced by P fertilizer and intercropping. In the maize/faba bean system, grain yields of maize were enhanced by N fertilizer while those of maize intercropped with wheat were improved by both N and P fertilizers. Grain yields of faba bean were not affected by fertilization or cropping system. Nitrate accumulation in soil was positively related with application rates of N fertilizer. The amounts of NO3− present in soil after wheat harvest was greatest under wheat planted alone, followed by intercropped wheat, faba bean planted alone, intercropped faba bean, maize intercropped with faba bean, and least under maize intercropped with wheat. Amounts of NO3− in soil after maize harvest was in the order of wheat or faba bean planted alone, intercropping wheat and faba bean, maize intercropped with faba bean and wheat. The results suggest that intercropping decreases the accumulation of nitrate in the soil profile. The study also showed that combined application of organic materials and N fertilizer decreased nitrate accumulation compared with application of N fertilizer alone.