Pea-maize intercropping has been a vital crop production mode in irrigated areas of Hexi Corridor in Gansu Province. However, there some problems of heavy fertilization while symbiotic N₂ fixation have been neglected in local crop production in the region. Thus, field trials were conducted in Wuwei City, Gansu Province, in 2011 and 2012 to study the effects of nitrogen fertilization and rhizobial inoculation on crop yield and water use efficiency in pea-maize intercropping system. The work aimed at determining an optimal nitrogen fertilizer application and rhizobial inoculation so as to save fertilizer and increase yields.

The results showed that while nitrogen fertilization had not significant effects on pea yield, yields of mono- and intercropped pea increased on average by 12.7% and 4.8%, respectively, after inoculation. Yield of intercropped pea increased by 61.1% on average compared to that of sole pea culture. Yield of monocropped pea was highest (2 735 kg·ha^-2) under nitrogen fertilizer rate of 75 kg·ha^-2 with inoculation. Under nitrogen fertilizer rate of 75 kg·ha^-2, pea yield increased by22.8% on average after inoculation. The effect of nitrogen fertilization on maize yield was significant. Yield of sole maize culture under nitrogen fertilizer rate of 300 kg·ha^-2 was 14 394 kg·ha^-2. Yield of intercropped maize was 61.8% higher compared to monocropped maize. Yield of maize intercropped with rhizobium-inoculated pea belt increased by 3.3% on average, compared with that intercropped with non-inoculated pea belt. Land equivalent ratio was larger than 1 under different treatments. The water use efficiency of pea reduced with increasing nitrogen fertilizer application, with the maximum value (12.9 kg·mm^-1·ha^-2) appearing under zero-N fertilizer use. Water use efficiency of maize first increased and then latter decreased under increasing nitrogen fertilization rate, with the maximum value (25 kg·mm^-1·ha^-2) appearing under nitrogen fertilizer dose of 300 kg·ha^-2.

Results show that the rate of nitrogen fertilizer application in maize for high grain yield and high water use efficiency was 300 kg·ha^-2 in pea-maize intercropping system. The recommended rate of nitrogen fertilizer application in pea for high grain yield and high water use efficiency is 75 kg·ha^-2 in pea-maize intercropping system. In filed production, pea yield significantly increased by the inoculation of rhizobia.