Legume-based green manure crops.

Abstract

Legume-based green manures (LGMs) are crops that are grown with the specific purpose of improving soil quality and consequently the long-term productivity of crops. Although the traditional focus has been on the supply of nitrogen (N) to the system, they have a wide range of potential benefits that include improving soil quality, reducing soil erosion and increasing the biodiversity of farmland. LGMs are a key component of organic farming systems where the use of synthetic N fertilizers is not permitted. However, increases in the cost of inputs, concerns about environmental impacts of intensive use of agrochemicals, and the recently announced measures for the 'greening' of the European Common Agricultural Policy have led to renewed interest in the use of LGMs more widely. In Europe, the legumes in LGMs may be annual or perennial plants, grown on their own or more often as part of crop mixtures with a range of other crop types such as grasses or brassicas. The legumes most commonly grown are the clovers (Trifolium spp.), particularly red and white clover. Other legumes that may be grown to suit particular local goals or constraints include Medicago spp. (lucerne (alfalfa) and black medic), trefoils (Lotus spp.), vetches (Vicia spp.), lupins (Lupinus spp.), other minor forage legumes and grain legumes. To maximize fertility building in organic farming systems, LGMs are grown in place of cash crops for some of the crop rotation. In more intensive systems, LGMs may be grown for short periods between phases of regular crop production. This chapter reviews the use of LGMs in Europe and considers factors that affect N fixation in them and the transfer of fixed N to following crops. It examines how they can be integrated into practical rotational cropping systems and whether the economics of this makes the use of LGMs profitable. However, LGMs will not be agronomically or economically viable in all systems, and in these cases other types of green manures may be more appropriate. As demand for multifunctional agricultural systems grows, and is increasingly required by European agricultural policies, so does the potential for greater use of LGMs.

Legume-Modified Rotations Deliver Nutrition With Lower Environmental Impact

“…Legume cultivation has been associated with other benefits, including diversification of crop rotations (Nemecek et al, 2008;Hufnagel et al, 2020) which can break pest and disease cycles (MacWilliam et al, 2014), improved soil quality and drought resistance through deep root systems, and support for pollinating insects (Peoples et al, 2019). Legumes are mainly grown for food and feed purposes (Nemecek et al, 2008;Watson et al, 2017), but they also supply value chains for, inter alia, alcoholic beverages (Lienhardt et al, 2019), biorefineries (Karlsson et al, 2015) or green manures (Baddeley et al, 2017).…”

Physiological and Biochemical Basis of Faba Bean Breeding for Drought Adaptation—A Review

“…Biological nitrogen fixation provides about 80% of the plant's nitrogen needs [7], reaching 160 kg ha −1 [7][8][9], and about half of the crop's fixed nitrogen content is left in the field after grain harvest. Hence, it is considered important for both its contribution to residual nitrogen in crop rotation [6] and its potential in green manuring [10].…”

Biological nitrogen fixation and prospects for ecological intensification in cereal-based cropping systems

“…Leaving the green manure on the soil surface as a mulch had the added advantage of smothering any weeds that otherwise might regrow, as well as preventing water evaporation, thereby ensuring good soil moisture for the cash crop. This practice has continued as an essential element of organic farming ( Baddeley et al, 2017 ): globally, all 3.3 Mha under organic cereal production ( Schott and Sanders, 2017 ) are likely to have benefited from N supplied by green manures.…”

“…Cover-cropping is another variation of green manuring that is increasingly being used by both organic and conventional farmers. This is particularly the case in the temperate climatic zones of Europe and North America, where the summer period is used primarily for crop production and winter is when the highest percolation of water through the soil occurs due to low evaporation and high precipitation ( Baddeley et al, 2017 , Kaye and Quemada, 2017 ). After harvest of the main crop in these agroecological systems the temperature and light conditions are still sufficient to support some plant growth, although not enough to produce a commercial cash crop.…”

“…Rather than leaving cropping land bare, cover crops of legumes (either alone or mixed with non-legumes) are now increasingly sown to lower the soil inorganic N content to reduce the risk of leaching and denitrification events during the fallow period ( Mueller and Thorup-Kristensen, 2001 , Thorup-Kristensen et al, 2003 , Plaza-Bonilla et al, 2017 ). After the cover crop is incorporated prior to sowing the next spring-summer crop, it effectively becomes a source of green manure and provides N benefits for subsequent crops ( Baddeley et al, 2017 ).…”