Soils and Sustainable Agriculture : Ecological Considerations

Sustainable agriculture can be defined in many different ways. In industrial nations, sustainable agriculture means improving energy use efficiency, reducing environmental pollution, and increasing and sustaining profitability. For millions of small-holder farmers throughout the tropics, sustainable agriculture means providing basic food needs for the farming family, improving the farmer’s ability to replenish soil nutrients and control soil degradation, and optimizing crop yield per unit area of land. Soil utilization for agricultural production in the tropics during the past two centuries, to a large extent, has been influenced by the technological and economic changes in temperate regions. Research and development for agriculture during the colonial era were mainly focused on the needs of industrial nations, while the production of food crops for the indigenous inhabitants was largely left in the hands of the traditional slash-and-burn cultivators. Large and small cash crop plantations were developed on fertile, high-base-status allophanic and oxidic soils for coffee, cocoa, banana, and sugarcane production throughout the humid and subhumid tropics. Cotton was cultivated on smectitic soils and high-base-status kaolinitic soils in the subhumid and semiarid regions of Africa for the textile industries in temperate regions. In tropical America, cattle ranching, a production system introduced by European immigrants, still occupies most of the fertile flat land today, while food grains are usually cultivated on less fertile land or in shallow soils on steep slopes. In tropical Africa and Latin America, a wide range of food crops, such as maize and beans, potato, cowpea, sorghum, millet, cassava, and yam are mostly produced under the traditional slash-and-burn system of cultivation on less fertile kaolinitic soils. In tropical Asia, the indigenous intensive rice-based agriculture on wet smectitic soil has been practiced over many centuries and has been able to meet the basic food needs for the increasing population in the region. Generally, upland food crop production in the tropics has not kept pace with human population growth in the tropics during the past century. It was not until the 1950s and 1960s, following the independence of many nations in tropical Asia and Africa, that more attention was given to the research and development of food crop production.