Perubahan status C-organik tanah mulai hutan sekunder hingga berbagai umur tanaman tebu pada ultisol

In the humid 'tropics soil organic matter maintainance plays an important role on sustainability of plant production. Understanding roles of soil organic matter in soil fertility canges after forest converted to agriculture land is for improved soil management strategy essential. The aims of this experiment were to study soil organic matter pools of intermediate turnover (2-10 years) are important for soil organic matter dynamic model. Acid soil (Ultisol) samples were collected at 0-15 cm depth from intact as well as recently converted forest to sugarcane plantation in North Lampung. Forest and sugarcane derived organic matter can be identified on the basis of the 13C/12C isotopic ratio. By analysis in this isotopic ratio on the whole soil and on soil fractionation obtained by sieving and density fractionation, the relevance of soil organic matter protection mechanisms such as clay-soil organic matter linkages can be quantified. Convertion of forest to sugarcane plantation caused decreased soil organic matter fraction. Isotopic 136 fractionation can be used as tool an to differentiate soil organic matter from forest (C3) and sugarcane (C4). After 10 years convertion of forest to sugarcane plantation, soil organic matter fraction derived from forest were light fraction 23% intermediate 44% and heavy 80%. Total C content of light fraction 67,5% intermediate and heavy fraction 67,3%. Carbon contribution of sugarcane were light fraction 0,40 Mg.ha-1, intermediate and heavy fraction 0,24 Mg.ha-1.