Nitrogen Fixation of Faba Bean (Vicia faba L.) Interacting with a Non-legume in Two Contrasting Intercropping Systems

Abstract

A field experiment was carried out to quantify biological nitrogen fixation (BNF) using the 15 N 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 N 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. There was yield advantage of maize/faba bean intercropping, but no in wheat/faba bean intercropping. The grain yield of the faba bean intercropped with maize was greater than that of faba bean monoculture due to increases of the stems per plant and the pods per stem of faba bean. N fertilization inhibited N fixation of faba bean in maize/faba bean and wheat/faba bean intercropping and faba bean monoculture. The responses of different cropping systems to N-fertilizer application, however, were not identical, with competitive intercropping (wheat/faba bean) being more sensitive than facilitative intercropping (maize/faba bean). Intercropping increased the percentage of N 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 kg N/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 shoot N derived from air (Ndfa), however, increased significantly when intercropped with maize, irrespective of N-fertilizer application. Ndfa decreased when intercropped with wheat, albeit not significantly at 120 kg N/ha. Ndfa was correlated more closely with dry matter yield, grain yield and competitive ratio, than with %Ndfa. This indicates that that total dry matter yield (sink strength), not %Ndfa, was more critical for the legume to increase Ndfa. The results suggested that N fixation could be improved by yield maximization in an intercropping system.

Root exudates drive interspecific facilitation by enhancing nodulation and N 2 fixation

“…We found that, when root interactions were possible (no root partition), faba bean biomass and grain overyielded by 35% and 61%, respectively, with no N fertilization (P < 0.0001) and when fertilized with 150 kg ha −1 N, overyielding percentages were 28% and 35%, respectively (P < 0.0001) (Table S1). These results are similar to those reported previously (7). Also,…”

“…Facilitation occurs when one species increases the growth of other species through a wide range of processes (10). Facilitative effects may be direct (e.g., by shade or protection from harsh conditions) or indirect (e.g., when one species reduces attack by pathogens or herbivores on other species) (11-13).Legume/cereal intercropping systems have been widely studied in the context of diversity and ecosystem function and commonly overyield, because dinitrogen (N 2 ) fixation by legumes increases ecosystem nitrogen (N) supply (7,8), an example of facilitation. This facilitation is important to agriculture on a large scale, because application of chemical N fertilizer decreases biological N 2 fixation by legumes.…”

“…Legume/cereal intercropping systems have been widely studied in the context of diversity and ecosystem function and commonly overyield, because dinitrogen (N 2 ) fixation by legumes increases ecosystem nitrogen (N) supply (7,8), an example of facilitation. This facilitation is important to agriculture on a large scale, because application of chemical N fertilizer decreases biological N 2 fixation by legumes.…”

“…A "sampling effect" occurs, because more diverse mixtures have a higher probability of containing a species with higher productivity (6). Complementarity effects occur when species vary in resource use and niche differentiation in space or time, leading to greater resource utilization (6)(7)(8)(9). Facilitation occurs when one species increases the growth of other species through a wide range of processes (10).…”

Growth and N2fixation in mixed cropping ofMedicago arboreaandAtriplex halimusgrown on a salt-affected soil using a15N tracer technique

“…It was previously observed that %Ndfa of the legume increased due to an N-sparing effect (N concentration in legume rhizosphere is reduced) by the non-legume (Danso et al 1987). A similar observation was also reported by a recent study (Fan et al 2006). Greater Ndfa% by intercropped legume could be further explained by the probable reduction of nitrate concentration in the rhizosphere due to higher nonlegume uptake of nitrate, which may reduce its toxic effect on Rhizobium (Kurdali et al 2003).…”