Mixed farming, the combined production of crops and livestock, is central to current and future global food supplies. Two thirds of all people, and most of the world’s poor, work in such systems to produce a significant proportion of key staple crops: 86 per cent of rice, 74 per cent of millet, 66 per cent of sorghum and 41 per cent of maize. In developing countries mixed farming systems also produce the bulk of animal-derived products: 75 per cent of milk and 60 per cent of meat.
Livestock provides nutrient-rich foods to farming households, a source of income and increased economic resilience in times of need – four out of the five commodities with highest global economic value, milk, beef, pork and chicken, come from animals. Livestock also contributes to farm productivity and supplies manure, both very important in rural areas of developing countries where the level of mechanisation and the availability of other fertilisers are often low and important constraints to productivity.
And, significantly, rates of growth in demand for and production and consumption of crops and animal products are higher in mixed farming systems than in other production settings.
As mixed farming systems in developing countries are key to food security, improving their productivity is important, especially in view of increasing food demands, and competing pressures on land, water and energy. Raising the productivity of crop-livestock production systems is also critical for environmental reasons. Livestock accounts for 14.5 per cent of all greenhouse gas emissions, with cattle contributing 60 per cent of these, with emissions linked to food digestion and feed production dominating emissions linked to ruminants. Livestock also accounts for about 39 per cent of total agricultural water use.
While the use of nitrogen and phosphorus fertilisers has enabled large increases in agricultural productivity, their excessive use leads to human health and environmental problems linked to groundwater pollution, excessive growth of algae in rivers and lakes, and the loss of habitats and biodiversity. Mixed farming systems are the largest human influence on global nitrogen and phosphorus cycles. While at the beginning of the last century the flow of nutrients in soils was balanced, between 1900 and 1950, surplus nitrogen doubled, and between 1950 and 2000 it rose to 138 million tonnes per year, a further four-fold increase. Surplus phosphorus had increased by a factor of eight by 1950, and increased five times again by 2000, to 11 million tonnes per year. Sustainable intensification, better integration of animal manure in crop production, and matching nitrogen and phosphorus supply to livestock requirements can effectively reduce environmental damage.
Improving the efficiency of livestock rearing by increasing the amount of animal product (by weight) produced per unit emission – reducing herd sizes without compromising production – is an important strategy for lowering environmental impacts. This includes using better feeds and feeding techniques that can reduce the amount of greenhouse gasses released during digestion as well as by decomposing manure. The close relationship in mixed farming systems between crop and livestock production makes it possible to substantially increase farm productivity. This is particularly important in sub-Saharan Africa, the region of the world with the lowest livestock productivity. Carbon sequestration in grasslands and improved management of grazing lands could improve productivity, potentially helping to reduce livestock emissions.
In developing countries, crops such as maize, wheat, sorghum, and millet serve a dual purpose: the grain is used as food for people and their residues as livestock feed. The importance of incorporating characteristics related to the nutritional quality of crop residues in plant breeding programmes is increasingly being recognised, as it has recently been shown that farmers in mixed production systems value the residues as much as the grain, particularly in the dry season. In Nigeria, for example, cowpea varieties were assessed for food and fodder characteristics including nitrogen, fibre and energy content and digestibility, uncovering high variability for these characteristics and highlighting the need to extend this type of study to increase overall plant value in mixed crop-livestock systems.
Improving the quality of forage crops is also critical in raising the productivity of mixed production systems. More than 600 species of grasses are currently used for grazing or feed, and most of the grasses used in the tropics originated in Africa. The next blog entry will review some of the challenges and opportunities linked to breeding programmes for forage crops.
Claudia Canales Holzeis is a plant molecular biologist with a near-decade of experience in plant genetics research. She previously worked as Senior Project Officer for the International Service for the Acquisition of Agri-Biotech Applications (ISAAA), based in the Philippines. A graduate of the University of Reading in Environmental Biology, Claudia Canales gained a DPhil. in Plant Genetics at Oxford.