Keywords :

Sharing major nutrient resources and uptake facilitation in intercropped cereal-legume systems: a case study on phosphorus

In light of the importance of ecological intensification in agrosystems, the phosphorus issue is especially worrisome because of the finite nature of natural phosphate resources, which is the main source of phosphate fertilizers. The shortage of these fertilizers will be a major problem within a few decades, so solutions are urgently needed. Among the promising innovations, UMR Eco&Sols; has launched an extensive research programme on the benefits of intercropping, as compared to monocropping, in making more effective use of soil nutrient resources. Many previous studies have revealed that cereallegume intercropping increases productivity, while also enhancing the quality of cereal production (protein contents) and nitrogen use, especially atmospheric nitrogen through more efficient symbiotic fixation. This is one factor behind the success of such cropping systems in developing countries and China, where intercropping systems are used on an area of around 25 million ha.

The hypothesis put forward is that, in addition to nitrogen, soil phosphorus could be better used by intercropping cereals and legumes than by separately monocropping these species. Studies carried out by UMR Eco&Sols; have shown that legumes (various tested grain legumes) and cereals (durum wheat) tap different soil phosphorus pools (organic/inorganic). Both species make more effective use of soil resources via this functional complementarity. Studies— especially long-term phosphate fertilization trials (40 years in 2009) carried out at INRA in Toulouse (France)—have also revealed nutrient uptake facilitation processes between intercropped species, i.e. the legume seems to be able to increase phosphorus availability in the associated durum wheat rhizosphere. Research is currently aimed at gaining insight into the underlying processes in order to come up with the best crop associations, especially under minimal phosphate fertilizer application conditions.