The aim of this study was to determine nitrogen use efficiency and reduce environmental pollution caused by excessive use of nitrogen fertilizer in pea-maize intercropping fields in irrigated areas of Hexi Corridor, Gansu Province. To that end, a field experiment was conducted in 2011 to determine the spatial and temporal distributions of soil inorganic N (Nmin) in orthic anthrosol soils under pea-maize intercropping at different N application rates (no application, 75 kg·ha^-2, 150 kg·ha^-2, 300 kg·ha^-2 and 450 kg·ha^-2). Soil samples were collected at 0-20, 20-40, 40-60, 60-80, 80-100 and 100-120 cm soil layer. Nmin concentrations were measured by flow analysis of extracted CaCl₂.

The results showed that NO₃^--N was the major form of Nmin in orthic anthrosol soils with a concentration 7.55 times that of NH₄⁺-N. During maize growth season, NO₃^--N concentration increased by 29.7%, 67.5%, 88.2% and 134.3% respectively under N rates of 75, 150, 300 and 450 kg·ha^-2 over no fertilization treatment. Compared with that after pea harvest, NO₃^--N concentration decreased by 44.2% after maize harvest. Soil NO₃^--N concentration in the 0-120 cm soil layer under intercropped pea-maize decreased respectively by 6.1%-5.1% over that of each corresponding monocultured crop. The highest soil Nmin accumulation occurred in the 0-20 cm soil layer at different nitrogen application rates and growth stages. After pea harvest, Nmin accumulation in the 0-60 cm soil layer under intercropped pea-maize respectively decreased by 4.9%-1.9%, and in the 60 -120 cm soil layer by 10.8%-9.2% compared with that of each corresponding monocultured crop. After maize harvest, soil Nmin accumulation in the 0-60 and 60-120 cm soil layers under intercropped pea-maize decreased respectively by 28.2%-9.4% and 23.5%-12.5% over each corresponding monocultured crop. Also soil Nmin residue in the 0-60 and 60-120 cm layers under intercropped pea decreased respectively by 4.9% and 10.9% over monocultured pea.

The study showed that nitrogen fertilizer application significantly increased soil inorganic nitrogen concentration and accumulation with higher effect on soil NO₃^--N. Also, excessive N application resulted in environmental pollution in the study area. Pea-maize intercropping significantly reduced soil inorganic nitrogen concentration and accumulation. It was obvious that intercropping reduced soil inorganic nitrogen accumulation especially in the later growth stages of the crops.