‘Nutrient pumps’ feed cattle, nourish maize
Many livestock farmers in Latin America have adopted a sustainable livestock production system that integrates forages with cereals. A key component of the system is Brachiaria, a grass native to sub-Saharan Africa, which grows well in poor soils, withstands heavy grazing and is relatively free from pests and diseases. Thanks to its strong, abundant roots, Brachiaria is very efficient in restoring soil structure, and helps prevent soil compaction, which reduces rainwater infiltration and stifles root growth. It also can convert residual soil phosphorus into organic, readily available forms for a subsequent maize crop. A chemical mechanism found in the roots of one Brachiaria species also inhibits nitrous oxide emissions from the soil. Emissions of nitrous oxide, which is one of the most potent of the greenhouse gases, are derived mainly from the application of mineral fertilizers.
While the adaptation of Brachiaria to low-fertility soils has led to its use for extensive, low-input pastures, it is also suitable for intensively managed pastures. In Mexico and Central America, the productivity of animals feeding on Brachiaria pastures is up to 60 percent higher than those feeding on native vegetation. The value of the additional production has been estimated at USD 1 billion a year. In Brazil, annual economic benefits have been put at USD 4 billion. Rotation of annual crops with grazed pasture is increasing in the Cerrados ecoregion of Brazil, where beef cattle are a major source of income for many farmers. Years of poor herd management, overgrazing and lack of adequate soil nutrient replacement have led to declining productivity and reduced profitability in traditional livestock production systems.
Where natural ecosystems have been replaced by intensive soybean monoculture, much of the soil is compacted and susceptible to erosion from heavy rainfall. Under those conditions, traditional techniques of soil erosion control, such as contour planting, have proved to be ineffective. In response, many farmers have adopted conservation agriculture, which increase soil cover and brings other environmental benefits. A typical sequence is maize or rice, followed by another cereal, such as millet or sorghum, or the grass Eleusine, intercropped with a forage species such as Brachiaria. The forages function as ‘nutrient pumps’, producing large amounts of biomass in the dry season that can be grazed or used as green manure. Combining maize and Brachiaria at the end of the rainy season taps soil water from levels deeper than 2 metres, and promotes active photosynthesis later during the dry season. This results in vigorous vegetative regrowth after the first rains of the following season, or after rain during the dry season, which ensures permanent soil cover.
Because Brachiaria provides excellent forage, farmers can then choose to convert the area into pasture, or keep it in grain production for another year. These systems are found in irrigated lands and in wetter regions with frequent, heavy rains that recharge deep water reserves. To reduce crop competition, novel intercropping systems have been developed. For example, in the Santa Fé system for maize and Brachiaria, developed in Brazil, the grass is made to germinate after the maize crop, either by delaying its planting or by planting it deeper. The young Brachiaria plants are shaded by the maize and provide little competition for the cereal. When the maize is harvested, however, shading is reduced and the established pasture grows very quickly over the maize residues.
The integration of forage and grain crops leads to a better use of the total farm area and a more intensive use of the pastures, with less pasture degradation. Similar systems are being tested in other parts of the world, including sub-Saharan Africa.
Source: adapted from FAO, 2015f