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| Nitrogen difference method is commonly used to appraise biological nitrogen fixation, which is a well established aspect of plant condition. In an intercropping system, belowground interspecific interactions affected the reliability of this method, so a field experiment was conducted to ameliorate this problem. A split-plot experiment was designed, with the main plot treatments of 0 and 225 kg N ha-1, and sub-plot treatments consisting of sole maize, sole faba bean, sole pea and sole soybean, and faba bean, pea and soybean intercropping with maize. Biomass of intercropping faba bean and pea was found to be increased, but soybean decreased significantly. Biomass of intercropping maize increased significantly than grown alone. Adding fertilizer nitrogen had no marked effect on biomass of the legumes, but that of maize increased. Aggressivity of faba bean (1.06~1.56) and pea (0.11~0.76) were always significantly greater than zero, but it was significantly decreased for soybean (-1.17~-0.81) than maize. Proportion of biological nitrogen fixation %Ndfa) increased for intercropping faba bean and pea than sole, and it was decreased for soybean due to a difference between legume and reference plant. Add nitrogen could decrease %Ndfa significantly for all legumes. An ameliorated nitrogen difference method was established, which takes into account the difference of nitrogen loss and interspecific nutrient competition. Compared with traditional methods, the %Ndfa of intercropping faba bean decreased significantly, and %Ndfa of intercropping pea decreased also, but %Ndfa of soybean increased. Since consider the nitrogen loss and interspecific nitrogen competition and transfer, the ameliorated method of NDM could appraise the proper %Ndfa of intercropping legumes more accurately. |
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| Keywords:Intercropping; Interspecific competition; Nitrogen loss; Nitrogen difference method |
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