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| A field experiment was carried out to quantify biological nitrogen fixation (BNF) using the 15N isotope natural abundance method in maize (Zea mays L.) / faba bean (Vicia faba L.) and wheat (Triticum aestivum L.) /faba bean intercropping systems. Faba bean was yielding more in the maize/faba bean intercropping, but not in the wheat/faba bean intercropping. Biomass, grain yield and nitrogen acquisition of faba bean were significantly increased when intercropped with maize, and decreased significantly with wheat, irrespective of N-fertilizer application, indicating that the legume could gain or lose productivity in an intercropping situation. N fertilization inhibited nitrogen fixation of faba bean in intercropping with either maize or wheat, and when used in monoculture. The response of different cropping system to N-fertilizer application, however, was not identical, with competitive intercropping (wheat/faba bean) being more sensitive than facilitative intercropping (maize/faba bean). Intercropping increased the proportion of nitrogen derived from air (%Ndfa) of the wheat/faba bean system, but not that of the maize/faba bean system when no N fertilizer was applied. When receiving 120 N kg/ha, however, intercropping did not significantly increase %Ndfa either in the wheat/faba bean system or in the maize/faba bean system in comparison with faba bean in monoculture. The amount of nitrogen derived from air (Ndfa), however, increased significantly when intercropped with maize, irrespective of N-fertilizer application. Ndfa decreased when intercropped with wheat, albeit not significance at 120 kg N/ha. Ndfa correlated more closely with dry matter yield, grain yield and competitive ratio, than with %Ndfa. This indicates that not %Ndfa, but total dry matter yield (sink strength) was more critical for the legume to increase Ndfa. The results suggested that nitrogen fixation could be improved by yield maximization in an intercropping system. |
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| Keywords:biological nitrogen fixation, maize/faba bean intercropping, wheat/faba bean intercropping, non-legume, interspecific interactions |
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