Ecological principles underlying the increase of productivity achieved by cereal-grain legume intercrops in organic farming. A review

Abstract

World population is projected to reach over nine billion by the year 2050, and ensuring food security while mitigating environmental impacts represents a major agricultural challenge. Thus, higher productivity must be reached through sustainable production by taking into account climate change, resources rarefaction like phosphorus and water, and losses of fertile lands. Enhancing crop diversity is increasingly recognized as a crucial lever for sustainable agro-ecological development. Growing legumes, a major biological nitrogen source, is also a powerful option to reduce synthetic nitrogen fertilizers use and associated fossil energy consumption. Organic farming, which does not allow the use of chemical, is also regarded as one prototype to enhance the sustainability of modern agriculture while decreasing environmental impacts. Here, we review the potential advantages of eco-functional intensification in organic farming by intercropping cereal and grain legume species sown and harvested together. Our review is based on a literature analysis reinforced with integration of an original dataset of 58 field experiments conducted since 2001 in contrasted pedo-climatic European conditions in order to generalize the findings and draw up common guidelines. The major points are that intercropping lead to: (i) higher and more stable grain yield than the mean sole crops (0.33 versus 0.27 kg m −2 ), (ii) higher cereal protein concentration than in sole crop (11.1 versus 9.8 %), (iii) higher and more stable gross margin than the mean sole crops (702 versus 577€ha −1 ) and (iv) improved use of abiotic resources according to species complementarities for light interception and use of both soil mineral nitrogen and atmospheric N 2 . Intercropping is particularly suited for low-nitrogen availability systems but further mechanistic understanding is required to propose generic crop management procedures. Also, development of this practice must be achieved with the collaboration of value chain actors such as breeders to select cultivars suited to intercropping.

Spatial diversification of agroecosystems to enhance biological control and other regulating services: An agroecological perspective

“…Introducing flower resources in these grass strips may also allow supporting flower visitors. Intercropping that provides benefits towards pest control can also lead to an increase of nitrogen and carbon in soils when leguminous plants are combined with cereals, potentially favouring soil fertility and reducing nutrient run-off with fewer fertilizer applications (Bedoussac et al, 2015;Cong et al, 2014). As for agroforestry systems, a recent meta-analysis shows that the introduction of trees generally reduces soil erosion, increases soil fertility and nutrient cycling as well as biodiversity (but the type of biodiversity, hence the functions it can exert, was not specified) (Torralba et al, 2016).…”

Luxembourgish farmers’ lack of information about grain legume cultivation

“…This statement was also mirrored in the agricultural utilised area of the two groups: farms which cultivated grain legumes had on average more agricultural utilised area (93.1 ha) and more farmland (48.9 ha) than those which did not cultivate grain legumes (88.6 ha utilised agricultural area, 41.8 ha farmland). However, grain legumes can be successfully used in rotation and intercropping systems (Bedoussac et al 2015) and can therefore also be incorporated in crop rotations on farms with less arable land. Here, the lack of knowledge on grain legume cultivation affects again the decision-making process.…”

“…Due to their ability to fix nitrogen from the air symbiotically with rhizobia species, legumes are very important in agriculture, especially in organic production (Bedoussac et al 2015). Legumes supply atmospheric N 2 to subsequent crops when grown in rotation and incorporated into the soil.…”

Sunflower crop: environmental-friendly and agroecological

“…Indeed, intercropping allows the increase of natural resources use efficiency by positive interspecific interactions (e.g. Bedoussac et al, 2015). Many studies on grain legume-cereal intercrops have shown advantages over the sole crops in low input systems such as the increase of the overall yield (sum of the species) and the grain protein concentration improvement of the cereal (e.g.…”

“…Many studies on grain legume-cereal intercrops have shown advantages over the sole crops in low input systems such as the increase of the overall yield (sum of the species) and the grain protein concentration improvement of the cereal (e.g. Bedoussac et al, 2015). In addition, intercropping warm-season crops constitutes a feasible alternative to promote hetero-geneity within-fields and therefore sustain biodiversity (weeds, B A Fig.…”