Smart Investments in Sustainable Food Production: Revisiting Mixed Crop-Livestock Systems
Abstract
Farmers in mixed crop-livestock systems produce about half of the world’s food. In small holdings around the world, livestock are reared mostly on grass, browse, and nonfood biomass from maize, millet, rice, and sorghum crops and in their turn supply manure and traction for future crops. Animals act as insurance against hard times and supply farmers with a source of regular income from sales of milk, eggs, and other products. Thus, faced with population growth and climate change, small-holder farmers should be the first target for policies to intensify production by carefully managed inputs of fertilizer, water, and feed to minimize waste and environmental impact, supported by improved access to markets, new varieties, and technologies.
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Science
Volume 327 | Issue 5967
12 February 2010
12 February 2010
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Copyright © 2010, American Association for the Advancement of Science.
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Published in print: 12 February 2010
Acknowledgments
This work was funded by the CGIAR Systemwide Livestock Programme. We acknowledge support from the Canadian International Development Agency, the World Bank, and the Swiss Agency for Development and Cooperation. We also thank M. Blummel, W. Thorpe, S. Staal, and S. Tarawali for useful discussions on the topic.
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Dung Use Affects Food Sustainability
In the Perspective "Smart investments in sustainable food production: Revisiting mixed crop-livestock systems" (12 February 2010, p. 822), M. Herrero et al. address an important topic of raising the productivity of crop-livestock systems practiced by small-holder farmers in developing countries. They argue that "in such systems, livestock provide draft power to cultivate the land and manure to fertilize the soil and crop residues feed livestock." In practice, however, the system breaks down because the manure is not used to fertilize the soil but to cook food in most rural households in South Asia, Southeast Asia, and Sub-Saharan Africa (1, 2). The amount of dried cattle manure used annually as cooking fuel in 1995 was estimated to be 35 to 108 Tg (1 Tg = 1012 g = 1 million metric tons) in India, 130 to 210 Tg in Asia, and 150 to 410 Tg, globally (3). The amount of animal dung used for cooking has been estimated to be as much as 128 Tg per year in India (4, 5), 1480 kg per household per year in Pakistan (6), and 0.2 kg per capita per day in Zimbabwe (7). Dung is also used in brick-making kilns in South Asia (8), and as a choice of fuel in Andean pottery production in South America (9). The combination of little or no dung used as manure, intensive grazing, and little or no application of chemical fertilizers has been a principal cause of the severe problems of soil degradation resulting in depleted soil organic matter (10), the decline in soil fertility in Sub-Saharan Africa, especially in Ethiopia (11), soil compaction, and accelerated erosion (12).
The flow chart in Fig. 1 (p. 823) can only function if: (i) viable sources of clean cooking fuel are identified so that dung is applied to soil as manure rather than used as cooking fuel, (ii) sustainable cropping systems are adopted in which forages are grown as an integral component of soil-specific cropping systems so that crop residues are returned to the soil, and (iii) small-holder farmers are compensated for ecosystem services (carbon sequestration, water conservation, biodiversity enhancement) to promote the replacement of extractive farming practices by sustainable management of soil and water resources. The conspicuous absence of these important factors in this and other reviews has contributed to agrarian stagnation, low agronomic yields, a perpetual food deficit, environmental degradation, and serious health hazards in developing countries.
Rattan Lal
School of Environment and Natural Resources, Kottman 210, Ohio State University, 2021 Coffey Road, Columbus, OH 43210, USA.
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