Push-Pull Farming System
Africa faces increasingly serious problems in its ability to feed its rapidly growing population, resulting in high hunger and poverty incidences. Growth in agricultural productivity is essential to reduce hunger and poverty and ensure food security. Agricultural growth can be achieved by reducing incidence of the major constraints to productivity such as pests, weeds and degraded soils. These constraints are responsible for the continent’s crop productivity being the lowest in the world, and cause high levels of hunger, malnutrition and poverty. Governments, donors and stakeholders in the Agricultural value chains recognise that in order to address hunger and poverty, these constraints must be effectively addressed. Therefore development and deployment of technologies that would improve sustainability and resilience of the farming systems are needed to contribute towards ending hunger and poverty in Africa and indeed the attainment of the Millennium Development Goals (MDGs). The main staple foods in the average African diet are cereals. However, in spite of availability of a number of cereal varieties with improved yield potential, the productivity of staple cereal crops remains low, around 1t/ha. Every year there is thus a critical shortage of cereals in many smallholder households, leading to high grain prices, hunger, undernourishment and widespread poverty. According to the World Development Report (2007), significant yield gains can be made by increasing the productivity of the cereal crops.
Sustainable solutions to the problems of yield loses to cereal crops caused by stemborers and striga weeds; and to the problem of declining soil fertility are best provided by the single 'Push-Pull' platform technology. Push-Pull simultaneously improves cereal productivity; enables production of year-round quality fodder from desmodium and Napier grass thereby allowing for integration with livestock husbandry; diversifies income streams and enables smallholders to enter into the cash economy; improves soil fertility and enables a minimum tillage system.
Push-Pull Farming System (https://www.youtube.com/watch?v=kBkawz0nq4Q#t=34)
The grasses are planted in the border around the maize and sorghum fields where invading adult moths become attracted to chemicals emitted by the grasses themselves. Instead of landing on the maize or sorghum plants, the insects head for what appears to be a tastier meal. These grasses provide the "pull" in the "Push-Pull" strategy. They also serve as a haven for the borers' natural enemies. Good trap crops include well-known grasses such as Napier grass (Pennisetum purpureum) . Napier grass has a particularly clever way of defending itself against the pest onslaught: once attacked by a borer larva, it secrets sticky substance that physically traps the pest and effectively limits its damage. The natural enemies lurking among the grasses go into action and dispatch the borers in both maize or sorghum and grass hosts plants.
The "push" in the intercropping scheme is provided by the plants that emit chemicals (kairomones) which repel stemborer moths and drive them away from the main crop (maize or sorghum). The best candidates discovered so far with the repellent properties are members of leguminous genus Desmodium spp. Desmodium is planted in between the rows of maize or sorghum. Being a low-growing plant it does not interfere with the crops' growth and, furthermore, has the advantage of maintaining soil stability, improving soil fertility through enhanced soil organic matter content and nitrogen-fixation. It also serves as a highly nutritious animal feed and effectively suppresses striga weeds. Another plant showing good repellent properties is molasses grass (Melinis minutiflora), a nutritious animal feed with tick-repelling and stemborer larval parasitoid attractive properties.
Stemborers, parasitic striga weeds and poor soil fertility are the three main constraints to efficient production of cereals in SSA. Losses caused by stemborers can reach as high as 80% in some areas and an average of about 15-40% in others. Losses attributed to striga weeds on the other hand range between 30 and 100% in most areas, and are often exacerbated by the low soil fertility prevalent in the region. The soils are highly degraded due to continuous cropping with limited or no external inputs to improve soil fertility. When the two pests occur together, farmers often lose their entire crop. Crop losses caused by stemborers and striga weeds amount to about US $ 7 billion annually, affecting mostly the resource poor subsistence farmers.
Control of stemborers using pesticides is not only expensive and harmful to the environment, but usually ineffective as the chemicals cannot reach deep inside the plant stems where stemborer larvae reside. Similarly use of herbicides against Striga is neither effective nor feasible among smallholders in the region for both biological and socio-economic reasons. Preventing crop losses from stemborers and striga weeds, and improving soil fertility in eastern Africa alone could increase cereal harvests enough to feed an additional 27 million people in the region.
A conservation agricultural approach known as `Push-Pull' technology has been developed for integrated management of stemborers, striga weed and soil fertility. Push-pull was developed by scientists at the International Centre of Insect Physiology and Ecology (icipe), in Kenya and Rothamsted Research, in the United Kingdom, in collaboration with other national partners. The technology is appropriate and economical to the resource-poor smallholder farmers in the region as it is based on locally available plants, not expensive external inputs, and fits well with traditional mixed cropping systems in Africa. To date it has been adopted by over 75, 297 smallholder farmers in East Africa where maize yields have increased from about 1 t/ha to 3.5 t/ha, achieved with minimal inputs. The technology involves intercropping maize with a repellent plant, such as desmodium, and planting an attractive trap plant, such as Napier grass, as a border crop around this intercrop. Gravid stemborer females are repelled or deterred away from the target crop (push) by stimuli that mask host apparency while they are simultaneously attracted (pull) to the trap crop, leaving the target crop protected. Desmodium produces root exudates some of which stimulate the germination of striga seeds and others inhibit their growth after germination. This combination provides a novel means of in situ reduction of the striga seed bank in the soil through efficient suicidal germination even in the presence of graminaceous host plants. Desmodium is a perennial cover crop (live mulch) which is able to exert its striga control effect even when the host crop is out of season, and together with Napier grass protect fragile soils from erosion. It also fixes nitrogen, conserves soil moisture, enhances arthropod abundance and diversity and improves soil organic matter, thereby enabling cereal cropping systems to be more resilient and adaptable to climate change while providing essential environmental services, and making farming systems more robust and sustainable.
Introductory Article by the Push-Pull Network Faming System