Effects of nitrogen fertilization application and faba bean/maize intercropping on the spatial and temporal distribution of soil inorganic nitrogen

A two-year field experiment was conducted to determine the spatial and temporal distribution of soil Nmin in orthic anthrosol soil under faba bean/maize intercropping at different N application rates (0, 75, 150, 225, 300 kg N/hm2), in Hexi Corridor of Gansu Province in 2006-2007. Soil samples were collected in 0-20, 20-40, 40-60, 60-80, 80-100, 100-120, 120-140, 140-160 cm soil layers by soil drill and Nmin concentrations in the soil were measured by flow analysis after CaCl2 extraction. The results showed that NO3--N is the major inorganic nitrogen form in orthic anthrosol soil, and there are no significant differences in soil Nmin accumulation between sole cropping and faba bean/maize intercropping at the co-growth stage. Soil Nmin accumulation in different soil layers was significantly reduced in the intercropping after faba bean harvest, compared to sole cropping. Soil Nmin was increased with nitrogen fertilization increasing. Soil Nmin accumulation in the intercropping in 0-100 cm soil layer is slightly greater than that of sole crop system at faba bean harvest, and greater than that in 100-160 cm soil layer. Soil Nmin accumulation in 0-100 cm soil layer was less by average 51.7% and 16.6% under faba bean/maize intercropping than corresponding sole crops, respectively, and by 42.1% and 6.1%, respectively, in 100-160 cm soil layer. Soil Nmin accumulations of faba bean and maize with nitrogen fertilzation in 0-100 cm soil layer were increased by 40.1% and 81.5%, over those without N fertilization, respectively, and were increased by 69.6% and 40.6% in 100-160 cm soil layer, respectively. Compared with the corresponding sole cropping system, Soil Nmin accumulations of faba bean/maize intercropping were decreased by 43.4% and 34.1% in 0-100 and 100-160 cm soil layer, respectively, after maize harvest. Therefore, soil inorganic nitrogen accumulation was increased significantly by N application, but was significantly reduced by legume/cereal intercropping.