Integrate legumes into field cropping systems
Intercropping entails growing two or more crops simultaneously, in the same field. Intercropping may be the best approach for areas with short rainy seasons. Spatial arrangement of the crops should make maximum use of the land. Some kind of row configuration is usually best for ease of management.
Figure 7a depicts a row of legumes alternated with a row of maize. In Figure 7b, the grain and legume are grown in alternate ‘strips,’ with each strip consisting of more than one row. Strip cropping reduces crop competition, but legume vines may not cover all of the ground underneath the cereal crop.
Intercropping of maize with cowpea in alternate rows (in South Africa; left-a) or in strips (ECHO Florida; right-b). The strip cropping photo (right) illustrates a system, developed in Nigeria by the International Institute of Tropical Agriculture, in which four rows of cowpea are alternated with two rows of maize; farmers were willing to devote fewer rows to maize because of the high value of cowpea grain. Source: Tim Motis
Relay cropping is a form of intercropping in which the legume is planted into a cereal crop shortly before the cereal crop is harvested. Sometimes the legume is planted only a few weeks after a main crop. However long, a delay gives farmers a way to integrate fast-growing, competitive legumes with staple grain crops. For relay cropping to work, the rainy season must be long enough to establish a delayed legume planting.
A grain and legume crop can also be grown on the same field–or portion of a field–during alternate seasons. This approach minimizes competition and the possibility of pests moving from the legume to a main crop. Crops can be rotated between blocks of space within a field to allow the farmer to grow a staple grain crop every year. Within each of these scenarios, including that of intercropping, rotation can be used to break weed and pest cycles. For example, legumes can be planted into rows that had been devoted to a cereal crop during a previous season; likewise, a cereal crop can be planted into rows previously planted to a legume.
The use of trees in CA is a form of “EverGreen Agriculture,” a concept in which trees are grown for fuel, fertilizer, food, fiber, and fodder. Trees can be integrated into the planting system in a number of ways:
Around the edges of a field
Planted around the border of a field, trees such as Gliricidia sepium can be used for live fencing.
Dispersed in fields at wide spacing
In lowland regions of the tropics, annual crop plants have been shown to benefit from 10 to 15 percent shade, achieved by planting trees 10 to 15 m apart.
In upland areas in Southeast Asia, fruit trees such as mango are sometimes dispersed in field cropping areas, which increases the diversity of farm products (Figure 9).
In parts of Africa, Faidherbia (Faidherbia albida) trees are grown in association with annual cereal crops and/or legumes. Faidherbia produces its leaves during the dry season, providing shade and a source of feed for animals during times of drought (Heuzé and Tran 2016). It then goes dormant during the rainy season, depositing an abundance of organic fertilizer (through leaves and pods that fall to the ground) and allowing light to reach the crops beneath the trees. This may not hold true in areas with both a short and long rainy season.
Farmer Managed Natural Regeneration (FMNR), a system developed in West Africa, takes advantage of an “underground forest” of already-existing stumps (from previously-cleared trees). These stumps are allowed to regrow, with the regrowth managed to facilitate annual crop growth and to supply firewood and/or timber. A similar approach, built on FMNR but with more intentional planting of edible acacias, is the Farmer Managed Agroforestry System (FMAFS).
A form of SALT in northeast India, in which perennial crops such as betel nut palm (Areca catechu) are grown between rows of Tephrosia candida. Perennials require less weeding than annual crops. Source: Rick Burnette
In rows along the contours of hillsides
Tree rows can be planted along the contours of hillsides, with annual and/or perennial crops planted in the space between tree rows. This is done in a system called SALT (Sloping Agricultural Land Technology), developed in the Philippines to reduce erosion on steep slopes. It incorporates crop diversification and mulch (tree prunings), and can be practiced using reduced tillage.
Incorporate plants with varying root traits
The mix of plant species, whether grown together or in sequence, should be selected with root traits—and related soil/microbial interactions—in mind.
Implement a disease and pest management strategy
Crop diversification can reduce incidence of pests. Legumes, for example, have reduced incidence of the plant parasite striga in cereal grains (Gworgwor 2002; Kureh et al. 2006). A good mix of crops, grown together or in sequence, fosters beneficial organisms yet minimizes the harboring of plant pests and diseases. Consider adopting an approach called Integrated Pest Management (IPM) to reduce the risk of a plant pest or pathogen spreading from one crop to another. IPM involves monitoring pests for timely intervention, growing healthy crops in conjunction with natural pest control, and limited use of pesticides. In a two-part IPM approach called “Push-Pull”, border plants attract (pull) insect pests to the edges of the field and intercropped plants repel (push) insects away from the main crop.