ABSTRACT
World soils vary greatly in soil organic matter (SOM) content ranging from 4 to 6% organic carbon (C) in the top 15 cm of some fertile soils to less than 0.5% in others. Organic matter content in soils of the tropics is important for several reasons. One, in soils with low activity clays, organic matter becomes an important sink or source of plant nutrients through its effect on cation exchange capacity (CEC). Two, by-products of mineralization of organic matter have important global impact on atmospheric concentration of these gases. There are four predominant agricultural land uses in the tropics, such as, arable, permanent/perennial crops, pastures and forest/woodlands. Conversion of tropical rainforest is considered to be a major factor in emission of greenhouse gases. Shifting cultivation is an important farming system of the tropics. The loss of C from soil profile under shifting cultivation is drastically less compared with loss of C under intensive cultivation.
