DEFINIMI; SUSTAINAflE AIiRIGULTUR r’OR TEE TP’IPIF^ b.&
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an the almost 60 countries that encompass the humid tropics grow enough food for their approximately 2 billion citizens without destroying their rain forests and other natural ecosystems? A committee of the National Academy of Science’s National Research Council has tackled that difficult question in a new report entitled “Sustainable Agriculture and the Environment in the Humid Trop-
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Pr6cis articles are reports of meetings of unusuol significance, international or notional developments of environmental importance, significant public policy developments, and related items.
BY ALAN NEWMAN ICS” (2). Their conclusion, as statea by committee chair Richard Harwood of Michigan State University, is: “It is not impossible to feed the worlds population while also managing and conserving our global resources.” The report supports that conclusion by evaluating how 12 land-use options would affect the environment, meet the resource needs of various countries, and might restore degraded land.
Recommendations In almost all of the countries the committee surveyed, the experts found examples of successful sustainable develonment and restora-
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tion of degraded lands. However, the key to success often depended not on science or technology, bu rather on social and political issues “The most important factor,” say Harwood, “is who owns and con trols the land. If individuals or lo calities are given long-term tenure to a tract of land, they have a strong incentive to use it efficiently an sustainahly.” In many cases, th, means “empowering” poor farmer Without that power, the landle: tend to grab what they can. “Just as health care is the Achilles heel that can destabilize the United States, so too these poor farmers can destabilize these countries.” The report also recommends that eovernments develon new markets
an says that Bali a service econtourism. “They :ulture be-
cause of runoff,so instead they have chosen high-value crops such as fruits.” These crops protect Bali’s natural beauty and in turn support tourism. On the other hand. laborintensive rice growing in the river deltas of Southeast Asia is possible because of the poverty there and the excellent growing conditions. The report also finds a need for agricultural research, especially on the land-use techniques developed by native peoples for their principal crops such as cassava, sweet potatoes, and cocoyams. As a result, sa rtant
strengthen local research facilities. Contributions from industrialized nations will also be necessary. However, the committee urged not just foreign aid, but rather a “partnership of equals.” This partnership would involve a flow of information between governments, policy-makers, researchers, and, according to Harwood, “most importantly. . .with the people who live on and work the land.” Finally, the report acknowledges but does not address the pressures of population growth that lead to environmental degradation.
Farming in the tropics
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Agriculture in tropical countries faces a host of impediments. Farmers in the tropics must contend with erratic rainfall; soils that are low in nutrients, highly acidic, and high in toxic aluminum; a constant assault by pests and diseases (which destroy an estimated 36% of the crops before harvest and another 14% after harvest); and aggressive weeds that grow year round. As a result, says the report, compared to intensive farming methods in temperate zones that can convert 2% of solar light into dry food matter through photosynthesis, growers in the humid tropics contend with an overall yield of no more than 0.2%. One solution is to borrow agricultural methods developed by indigenous peoples. Of the land-use methods surveyed in the report, the most controversial is “shifting cultivation,” which often involves the periodic burning of trees and shrubs, or slash-and-burn. One of the most widespread agricultural practices in the tropics-practiced on about 30% of the world’s arable lands-slashand-burn has been condemned for destroying rain forests, increasing atmospheric CO, and haze levels, and promoting soil erosion. However, the report found a role for slash-and-burn in sustainable agriculture. “Shifting cultivation, when done properly, is the best way to handle forests,” says Ariel Lug0 of the Department of Agriculture’s Forest Service in Puerto Rico. The key is to maintain a fallow period long enough to allow nutrients to recycle and organic material to build up in the soil. In some places that can be a few years, but in other locales it should be as long as 40 years. Unfortunately, i n many places economic pressure has shortened the fallow periods, leading to degradation of the soil. Other potentially sustainable agricultural practices combine activities that work together to benefit the land and the farmer. For instance, agropastural systems unite animal and crop production. One example is rice farming employing water buffalo for cultivation. In addition to labor, the animals supply meat and milk. An allied concept is agroforestry, which mingles trees (e.g., for windbreaks or firewood) with agricultural products. Another indigenous technique involves mixed tree systems. Often found in home gardens and small orchards, this approach protects
1006 Environ. Sci. Technol., Vol. 27, No. 6, 1993
soil while providing products ranging from fruits and nuts to medicines. Moreover, this technique can minimize weeding and pest management through the intermixing of plants, use of shade trees, and grazing of domestic animals. The different crops can also ensure agricultural products year round. Harwood cites the example of Sumatra, where intensive planting of a variety of trees produces food for local consumption and spices for exports, and allows space to raise animals, while supporting as many as 500 people per km’. As an agricultural method, these mixed tree plots contrast with the modern system in which single crops such as rubber or coffee are planted in large plantations. Singlecrop operations are more accessible for mechanized farming, usually generate higher profits, and produce badly needed products for export. The report finds that most of the high-quality land suitable for intensive plantation farming in the tropics has already been exploited. With proper care, these lands can remain productive, but the report suggests reforms such as integrating crops to maintain the land, mulching to destroy weeds, and terracing to reduce erosion, Plantations can even reclaim deforested lands. Similar approaches apply to cattle ranching in the tropics. The lack of soil nutrients needed to support grasses on pasture land has led ranchers to clear new areas in virgin forests. According to the report, in the Brazilian Amazon alone there are 5-10 million hectares of severely degraded pasture land. Reclaiming these degraded lands as well as deforested regions could fulfill much of that region’s need for new pasture land, reducing the pressures to open new regions. Harwood warns that sustainable agricultural practices must be implemented soon in the tropics. “Timing is critical. Within a generation, some regions stand to be degraded beyond hope of economically feasible restoration, losing almost all forest cover and productive soil.”
Reference (1) “Sustainable Agriculture and the En-
vironment in the Humid Tropics”; National Academy Press: Washington, DC, 1993.
Alan Newman is an associate editor on the Washington staff of ES&T.
