Nutrient availability in degraded soils of warm areas: The role of fertilizers in the process
1990
Leon, L.A. (International Fertilizer Development Center, Cali (Colombia). Agro-Economic Division)
Soils can be degraded due to many factors, including erosion, loss of nutrients by leaching, excessive soil tillage, imbalanced application of fertilizers, poor irrigation management, etc. In many of these degraded soils, the main problems are nutrient deficiencies and acidity or alkalinity which constrain the normal plant development. In many of the warm lowland soils of tropical Africa, Asia, and Latin America with high annual rainfall, nutrient deficiencies are common, with phosphorus, nitrogen, potassium, calcium, magnesium, sulfur, zinc, and boron being the most important. In addition to these problems, low organic matter content and high exchangeable aluminum saturation are common in these soils. Some soils are also high in manganese or iron and sometimes, especially under flooded conditions, rice plants exhibit toxicity symptoms. Physical problems of hardpan or surface crust formation, which restrict water penetration and downward movement, are sometimes present. Soils with excess of salts and/or sodium can also present some problems of nutrient unavailability, generally P, N and micronutrients such as Zn, Fe, copper, Mn, and B. Fertilizers and amendments play a important role in the solution of these problems. Generally, the topography and physical conditions of these soils are excellent for planting high yielding annual crops, but their chemical properties limit yields of improved varieties. The use of balanced fertilizer applications is of great importance not only to obtain high yields, but also to restore or increase soil fertility
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