Nitrate Accumulation In Soil And Nutrient Acquisition By Intercropped Wheat, Maize And Faba Bean

Intercropping is a practice quite possibly as old as settled agriculture, it is becoming more important to raise crop productivity in order to meet the increasing food requirement of an increasing population all over the world. Intercropping, through more effective use of water, nutrients and solar energy, can significantly enhance crop productivity compared to sole crops. This field experiment, with split-split-plot design including N fertilizer, P fertilizer and intercropping and monocropping treatments, integrated the wheat/maize and maize/faba bean intercropping system to assess the effects of intercropping on interspecific facilitative and competitive interactions between intercropped species under various application rates of N and P fertilizers. The emphases were laid on the nutrient uptake by crops and nitrate accumulation and distribution in soil profile. The field experiment was conducted in Gansu province, northwest part of China. The results were as follows: (1) The grain yield of wheat was significantly enhanced by P fertilizer and intercropping, while the one of intercropped maize was improved by both N and P fertilizers. The grain yield of faba bean was not affected by fertilization or cropping pattern. At the same fertilization rate, the grain yield of maize intercropped with faba bean was much higher than that of intercropped with wheat. (2) The yields in the border rows of intercropped wheat were higher than in the inner rows, which was the main reason for total grain yield increase. The border row yield advantage was obvious under low N application conditions and reduced with the increase of N fertilizer. (3) Both the application of N and the intercropping could enhance the N concentration in grain and straw of wheat, the amount of N uptake by wheat was also increased by N fertilizer. The N concentration in maize was relative to N fertilizer application. Both intercropping and N fertilizer could enhance the amount of N uptake by maize. (4) Phosphorus uptake by intercropped wheat was higher than that by sole wheat, both N fertilizer and intercropping also enhanced the amount of P uptake by maize. The P concentration in grain and straw of wheat and maize was not affected by fertilization and intercropping. (5) Nitrogen and P uptake by maize intercropped with faba bean was higher than that of intercropped with wheat. (6) Under low N application, the increase of total N uptake was attributed to the border row advantages, but the increase under high N conditions was due to of both border and inner rows. As for P, the border row advantages always existed regardless of P fertilization. (7) Nitrate accumulation in soil was positively related with application rates of N fertilizer. The amounts of NO₃^-presented in soil after wheat or faba bean harvest was the greatest under sole wheat, followed by intercropped wheat, sole faba bean, intercropped faba bean, maize intercropped with faba bean, and least under maize intercropped with wheat. But the sequence of that after maize harvest was sole wheat and faba bean, intercropped wheat and faba bean, maize intercropped with faba bean and wheat. The results suggest that intercropping could decrease the accumulation of nitrate in soil profile. From long-term fertilization experiment, it could be concluded that the reasonable combination of organic matter and N fertilizer might also lower the nitrate accumulation in soil. (8) The possibility of nitrate leached to deeper soil profile was enhanced with the increase of N fertilizer.