Jonathan Odhong’, Africa RISING program Communication and Knowledge Sharing Coordinator, IITA
Depleted soils are a major underlying cause of poverty and hunger in Africa. With a bulging population currently pegged at 1.2 billion people and at least 20% being food insecure, food and nutritional demands must be met without further degrading the natural environment. Therefore, recommended technologies of crops and cropping systems that promote soil sustainability should be encouraged to contribute to the fight against poverty and hunger.
Legume crops play a vital and multipurpose role. In addition to serving as a source of high-quality food and feed, leguminous crops also fix atmospheric nitrogen into the soil to improve fertility, enhance soil structure, and add organic matter to the soil. They can also be used as an intercrop when planted with cereals for diversified farm production and cover crops to reduce erosion and weed pressure on farms. These crops can
therefore contribute to achieving the objectives of sustainable food production and environmental security.
Over the past six to eight years, IITA researchers, collaborating with various partners, have developed and shared three legume-based technologies that are helping smallholder farmers in West, East, and Southern
Africa rejuvenate their soils while keeping their plates full. These technologies are: (a) the doubled-up legumes technology, (b) optimal spacing for groundnut, and (c) conservation agriculture in maize–legume systems.
Funded by USAID through the Africa Research in Sustainable Intensification for the Next Generation (Africa RISING) program, each of these technologies has proven effective in boosting soil fertility, improving family
nutrition, and other tertiary benefits documented through a broader sustainable intensification assessment.
Doubled-up legumes technology
The doubled-up legumes system is based on intercropping grain legumes, with pigeon pea (Cajanus cajan) as one component— increasing the total legume yield per unit area. Doubling-up legumes fulfills multiple
objectives, including (a) integrating more grain legumes when land is limiting, (b) rehabilitating fields with poor soil fertility, and (c) extending ground cover in cropped lands as pigeon pea can be in the field for 6 to 8 months, depending on the variety used.
Intercropping two grain legumes exploits their complementary growth habits and plant architecture. The most successful doubled-up legumes system is pigeon pea with groundnut (Arachis hypogaea). Both crops are
planted at their typical monocrop densities (additive) or one or both crops are planted at a lower density (partial substitutive), depending on the level of water stress in a site. Groundnut and pigeon pea are planted at the same time. Pigeon pea grows very slowly during the first three months, only starting rapid growth as the groundnut approaches maturity. After groundnut harvest, pigeon pea grows as a sole crop. Groundnut is
often considered the main crop in the intercrop and is planted at its ordinary ‘sole cropping’ density. Pigeon pea is planted at 50–100% of its sole cropping density.
Large-scale research and scaling were done in the central districts of Malawi (Dedza and Ntcheu). In 2017, the Government of Malawi officially ‘released’ the doubled-up legumes technology as an innovation that can be mainstreamed across the country for soil fertility improvement and improved human nutrition outcomes.
Michigan State University, LUANAR, IITA, and Malawi’s Department of Agricultural Research Services.
Optimal spacing for groundnuts in smallholder farming systems
Africa RISING scientists have found that increasing the groundnut planting density confers numerous benefits. The new technology specifies an inter-row spacing of 30 cm and intra-row spacing of 15 cm, giving a 22 plant per square meter planting density. Compared with farmers’ traditional practices, the higher density of plants increases the rate of canopy closure over the soil surface by 25% at every 10-day interval from 30 days after planting to harvest. The more profuse plants and the earlier closure of the canopy over the soil improve the soil microclimate, conserve moisture, and enhance plant growth. It also protects the soil from erosion and improves water infiltration and soil moisture retention.
Grain yields increased by 85% in on-farm trials and fodder yields by 42% compared to conventional planting density. Feeding groundnut haulm from the 22 plants per square meter density to sheep increased dry matter digestibility by 28% and live weight gain by 85%. It also improved the nitrogen concentration of the manure by 12% when compared with that of sheep fed with groundnut fodder from the conventional planting
density. Additionally, biological nitrogen fixation is boosted by 56% relative to conventional practices, while reduced weed infestation is another key benefit.
The technology was validated jointly with farmers in six districts and 12 communities of northern Ghana during the 2016, 2017, and 2018 cropping seasons.
Conservation agriculture in maize–legume systems
Conservation agriculture is a crop management system based on three main principles: (a) minimum soil movement (no soil inversion, i.e., no-tillage); (b) surface cover with crop residues and/or living plants; and (c) diverse crop rotations or intercropping strategies. The technology can be supported and improved with additional crop management practices, Annual Report 2020 51 such as timely application of operations, the precision of seeding, adequate application of nutrients, and efficient control of weeds and pests, including the use of herbicides.
In Malawi and eastern Zambia, farmers practice manual conservation agriculture systems with maize by making small planting holes with a pointed stick (dibble stick) or hoe. The seed is then planted in rows at a spacing of 25 cm between plants and 75–90 cm between rows. For rotational legumes, the spacing can be halved (to 37.5–45 cm while maintaining in-row spacing at 25 cm) to make full and more efficient use of the land area. Cereals and legumes can also be grown as intercrops under no-tillage in the conservation agriculture system.
The technology was validated extensively in southern and central Malawi and eastern Zambia through long-term conservation agriculture trials. An estimate of more than 1 million farmers in Malawi and Zambia have adopted conservation agriculture.
Partners: CIMMYT and IITA