An adequate supply of plant nutrients is essential for efficient
crop production on the highly weathered and leached soils of the humid tropics.
Effective nutrient management requires two steps: (i) increase nutrient reserves
in the soil and their availability to crops; and (ii) assess the nutrient
requirements of the crops to be grown. Effective nutrient management involves
meeting the nutrient requirements for expected yields from soil reserves and
supplemental additions of chemical fertilizers and organic manures. Most soils
of the humid tropics (e.g., Oxisols, Ultisols, and Alfisols) are low in nutrient
reserves. Therefore, it is necessary to supply nutrients from external sources.
There are diverse sources of nutrients, including chemical fertilizers,
biological nitrogen fixation, and nutrient