Fertilizers for Tropical and Subtropical Agriculture
Donald L. McCune
Agriculture in the tropics and subtropics must become much more efficient and productive if the food, fiber, building materials, and energy needs of developing countries are to be met. Increasing amounts of suitable fertilizers must be physically and economically available to farmers in these areas if their agricultural goals are to be attained. Fertilizers and fertilizer practices that meet the specific needs of the tropics and subtropics must be tailored to the crop, soil, climate, and socioeconomic factors that prevail. With ever-increasing costs of raw materials, processing, and transportation, more attention must be given to the increased efficiency and recovery of applied nutrients. The International Fertilizer Development Center (IFDC) was created in 1974 to develop new and improved fertilizers and fertilizer practices for developing countries with particular emphasis on tropical and subtropical agriculture. Nitrogen studies have focused on more efficient use of urea because urea is the primary nitrogen fertilizer available to farmers in developing countries and often the only one. The efficiency of urea can be improved through deep placement in the soil, coating of urea granules to control the urea release rate, split applications, and improved management practices. Overall nitrogen efficiency can be enhanced by supplementing chemical nitrogen fertilizers with biological nitrogen fixation, recycling organic matter, including green manures, and adequately balancing nutrients. Phosphorus deficiencies can be overcome by directly applying phosphate rock under certain conditions, using partially acidulated phosphate rock, and using thermophosphate in some tropical regions. Greater use of indigenous resources must be encouraged. Additional attention must be given to overcoming severe sulfur deficiencies and providing a balance of nutrients through improved products and practices. More emphasis must be placed on identifying and correcting secondary elements and micronutrient deficiencies in tropical agriculture. The fertilizer industry cannot serve tropical agriculture effectively by supplying primary nutrients only.