Grain legume–cereal intercropping systems

Grain legumes are widely cultivated, particularly for their dry seeds (known as pulses). Grain legumes are an important crop for a number of reasons. They are a rich source of protein and fibre, minerals and vitamins. In addition, their rapid growth and ability to fix nitrogen and improve soil health makes them a key rotation crop in the sustainable intensification and diversification of smallholder farming. This makes grain legumes a key food security crop. However, yields in developing countries are low as a result of such factors as the need for improved varieties of seed, poor seed distribution, the impact of pests and diseases, as well as vulnerability to poor soils, drought and other effects of climate change.
This chapter summarises data from over 50 field experiments undertaken since 2001 on cereal-grain legume intercropping in 13 sites in southern and western France as well as in Denmark using spring and winter cereal-grain legume intercrops. Intercropping involves simultaneously growing two or more crops in the same field for a significant period of time. The practice is ancient as early records from many human societies all over the world have shown. Intercropping systems are estimated to still provide as much as 15–20% of the world’s food supply. The practice was widespread in some European farming systems up until the 1950s – before the so-called fossilisation of agriculture. At that time as much as 50 % of all available nitrogen (N) may have originated from symbiotic N2 fixation by leguminous food, forage and green manure crops used in rotation which limited the reactive N coming from fertilizer-N and then the negative impact of NO3, NH3 and N2O on the environment. In those systems, land was dedicated to fertility generating legume rotations, which potentially also contributed to other ecosystem services such as carbon sequestration and biodiversity. Despite these advantages, grain legume cropping is less favoured now, even in organic crop rotations, because of a reputation of low yield and instability related to several factors like intolerance to water stress, harvest difficulties because of lodging, pathogen attacks, sensitivity to insect pests and weed competition. Aiming at higher crop diversity, intercropping is an interesting option to introduce legumes in cropping systems in a more efficient way compare to sole cropping rotations.