Effects Of Nitrogen Fertilizer Application And Rhizobia Inoculation On Crop Yields, Water And Nutrient Utilization In Pea/maize Intercropping Systems

Pea/maize intercropping has been practiced popularly by local famers in the irrigated areas of Hexi Corridor in Gansu Province. However, there are some problems with over fertilization and inhibited symbiotic N2 fixation of pea in the systems. Thus field trials were conducted in Wuwei City of Gansu Province in 2011 and 2012 to study the effects of nitrogen fertilization and rhizobia inoculation on crop yields, water use efficiency, and the above-ground N P K utilization, spatio-temporal distribution of soil inorganic nitrogen in soil profiles under pea/maize intercropping. 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 main results obtained were as the following:(1) While nitrogen fertilization had not significant effects on pea yield, yields of monocropped and intercropped pea with rhizobium inoculation were increased on average by 12.7% and 4.8%, respectively,compared to without rhizobium inoculation.Yield of intercropped pea increased by 61.1% on average compared to that of monocropped pea. Yield of monocropped pea with inoculation was highest(2735kg·hm-2) under nitrogen fertilizer rate of 75 kg·hm-2. Applying 75 kg·hm-2 of nitrogen fertilizer and innoculating with rhizobium, pea yield increased by 22.8% on average, compared with without rhizobium inoculation. There were significant responses of maize yields to nitrogen fertilization. Yields of monocropped maize under nitrogen fertilizer application rate of 300 kg N·hm-2 was 14394 kg·hm-2 and yields of intercropped maize increased by 61.8% compared with that of monocropped maize.(2) Pea/maize intercropping had significant yield advantages, where adequate N fertilization enhanced water use efficiency. Land equivalent ratios(LERs)based on either grian yields or above-ground biomass were greater than 1.0 for pea/maize intercropping regardless of nitrogen fertilizer application or not. The water use efficiency of pea reduced with increasing nitrogen fertilizer application, with the maximum value(12.9kg·mm-1·hm-2) appearing under zero-N fertilizer use. Water use efficiency of maize first increased and then latter decreased with increasing nitrogenfertilization rates, with the maximum value(25kg·mm-1·hm-2) appearing at nitrogen fertilizer rate 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.(3) During the maize growth season, the above-ground biomass of crop of intercropped pea increased by 44.6% on average compared to that of monocropped pea. Respectively, intercropping was attributable to improved the above-ground nutrient content and nutrient accumulation to increase biomass and grain production.The N P K nutrient accumulation of intercropped pea increased by 40% on average compared to that of monocropped pea.Yield harvest index was significantly higher in intercropped maize than in sole maize, The harvesting index was 89.0% and 6.5%higher in intercropped maize than in sole maize received 0 and 300 kg N·hm-2,respectively. The above-ground N, P and K harvest index were 79%,91%,and 47%at 75 kg·hm-2 of nitrogen fertilizer application rate. The above-ground N, P and K harvest index under nitrogen fertilizer of 300 kg·hm-2were biggest by 57%, 77% and16%, respectively.(4) Water requirement niche separation for pea and maize was one of mechanisms underlying efficient water utilization in the intercropping. At the pea seedling stage and the pea filling stage, soil water contents under intercropped pea was higher than those under corresponding sole pea, and the contents under maize was greater than those under pea. And the soil water content in intercropped pea was decreased compared with corresponding sole crop after the pea harvesting and maize harvesting. At the maize seedling stage and the maize raising knob stage, soil water content in intercropped maize was higher than in corresponding sole maize. And the soil water content in intercropped maize was decreased compared with corresponding sole crop after the pea harvesting and maize harvesting, and the water content in soils under pea was greater than those huder maize.(5) Fertilization enhanced soil inorganic nitrogen content, but intercropping was able to reduce the concentration. The results showed that NO3?-N was the major formof Nmin in orthic anthrosol soils with a concentration 7.55 times that of NH+ 4-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·hm?2over no N 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 by6.1%/5.1% over that of each corresponding monocultured crop.(6) Fertilization increased the soil inorganic nitrogen acumulation, but intercropping was able to reduce the residual mineral N in soils relative to monocropped crops. 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/maize decreased respectively by 4.9% and 10.9% over each corresponding monocultured crop. The study showed that nitrogen fertilizer application significantly increased soil inorganic nitrogen concentration and accumulation with high effect on soil NO3?-N. 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.