Effects of nitrogen fertilizer application and rhizobial inoculation on yield and water use efficiency of pea/maize intercropping system

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 and symbiotic N₂ fixation neglect have persisted in local crop production in the region. Thus field trials were conducted in Wuwei City of Gansu Province in 2011 and 2012 to study the effects of nitrogen fertilization and rhizobial inoculation on crop yield and water use efficiency of pea/maize intercropping system. The work aimed to determine an optimal nitrogen fertilizer application and rhizobial inoculation so as to save fertilizer and increase yield of pea/maize intercropping system. The results showed that while nitrogen fertilization had not significant effects on pea yield, yields of monocropped 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 monocropped pea. Yield of monocropped pea was highest (2 735 kg·hm^-2) under nitrogen fertilizer rate of 75 kg·hm^-2 with inoculation. Under nitrogen fertilizer rate of 75 kg·hm^-2, pea yield increased by 22.8% on average after inoculation. The effect of nitrogen fertilization on maize yield was significant. Yield of monocropped maize under nitrogen fertilizer rate of 300 kg·hm^-2 was 14 394 kg·hm^-2 and yield of intercropped increased by 61.8% compared with that of 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·hm^-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·hm^-2) appearing under nitrogen fertilizer dose of 300 kg·hm^-2. From the above results, it was recommended that the rate of nitrogen fertilizer application in maize for high grain yield and high water use efficiency was 300 kg·hm^-2 in pea/maize intercropping system. Then the recommended rate of nitrogen fertilizer application in pea for high grain yield and high water use efficiency was 75 kg·hm^-2 in pea/maize intercropping system. In filed production, pea yield significantly increased by the inoculation of rhizobia.