The effect of intercropping on the efficiency of faba bean – rhizobial symbiosis and durum wheat soil-nitrogen acquisition in a Mediterranean agroecosystem

The aim of this study was to compare the rhizobial symbiosis and carbon (C) and nitrogen (N) accumulations in soil and plants in intercropping versus sole cropping in biennial rotation of a cereal-durum wheat (Triticum durum Desf.), and a N-2-fixing legume-faba bean (Vicia faba L.) over a three-year period at the INRA (National Institue of Agronomic Research) experimental station in the Mauguio district, south-east of Montpellier, France. Plant growth, nodulation and efficiency in the use of rhizobial symbiosis (EURS) for the legume, nitrogen nutrition index (NNI) for the cereal, and N and C accumulation in the soil were evaluated. Shoot dry weight (SDW) and NNI were significantly higher for intercropped than for the sole cropped wheat whereas there was no significant difference on SDW between the intercropped and sole cropped faba beans. EURS was higher in intercropped than in sole cropped faba bean. Furthermore, by comparison with a weeded fallow, there was a significant increase in soil C and N content over the three-year period of intercropping and sole cropping within the biennial rotation. It is concluded that intercropping increases the N nutrition of wheat by increasing the availability of soil-N for wheat. This increase may be due to a lower interspecific competition between legume and wheat than intra-specific competition between wheat plants, thanks to the compensation that the legume can achieve by fixing the atmospheric nitrogen.