Abstract
Commercial legume varieties vary in terms of their drought tolerance when grown as sole crops, though relatively little is known about how legume variety selection affects cereal–legume intercrop performance under drought conditions. This study aims to test the hypothesis that positive rhizosphere interactions in faba bean–wheat intercrops will confer a “buffering capacity” on faba bean and wheat performance under water stress and that this effect will (i) depend on faba bean varietal selection and (ii) be enhanced with increasing faba bean varietal diversity. In a greenhouse experiment, three commercial faba bean (Vicia faba L.) varieties [Gloria (G), Alexia (A), Julia (J)] were grown in sole crop or intercropped with spring wheat (Triticum aestivum L.) under well-watered or water-stress conditions. Under intercropping, either one, two, or all three faba bean varieties were grown together with wheat to test the effect of intraspecific diversity on a cereal–legume intercrop performance. Consistent with the proposed hypothesis, we found that, under well-watered and water-stress conditions, wheat and faba bean shoot biomass production and nitrogen (N) acquisition improved with intercropping and that faba bean variety and variety mixture strongly modulated the intercropping effect. Interestingly, in both well-watered and water-stress conditions, wheat dry biomass and N accumulation were greatest in intercrops containing Gloria, while nodule number, nodule weight, and N accumulation in faba bean were greatest for intercrops containing Alexia and Julia (AJ). The effect of varietal diversity was inconsistent. Intercrops with two faba bean varieties tended to have positive or neutral effects on measured wheat and faba bean variables. However, overall performance under intercropping was generally reduced when all three faba bean varieties were planted with wheat. The effect of faba bean species diversity can buffer faba bean–wheat intercrop performance against water stress, and intercropping tended to have positive or neutral effects on the measured wheat and faba bean variables, notably with two-varietal faba bean mixtures.
Highlights
Intercropping is an agroecological land management practice where at least two crop species are grown on the same field at the same time (Wezel et al, 2014)
Wheat and Faba Bean Biomass Accumulation in Shoots and Roots. Both cropping and water treatments influenced biomass dry matter accumulation in wheat and faba bean shoots (Figures 1A, 2A). In both well-watered and water stress treatments, intercropping wheat with faba bean typically increased wheat shoot dry weight (DW) per plant over that achieved in wheat sole crop (Figure 1A), while water stress significantly decreased wheat and faba bean shoot DW per plant irrespective of the cropping treatment
In both well-watered and waterstress conditions, wheat intercropped with the faba bean Alexia variety, and to a lesser extent with Julia, had greater shoot when intercropped with water stress for Alexia and Gloria (WAG) and with both Alexia and Julia (WAJ), where root DW increased by 50% compared to the well-watered treatment (Figure 1B, Supplementary Figure 1)
Summary
Intercropping is an agroecological land management practice where at least two crop species are grown on the same field at the same time (Wezel et al, 2014). Cereals can outcompete legumes for soil mineral N, reducing soil N availability and subsequently stimulating SNF of the legume (Unkovich and Pate, 2000). This has been shown to result in higher total N uptake per unit of land in cereal–legume intercrops compared to sole crops (Bulson et al, 1997; Hauggaard-Nielsen et al, 2008, 2009; Li et al, 2009; Lithourgidis and Dordas, 2010), in perennial intercrops
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