Contents and dynamics of soil carbon in integrated crop-livestock systems

The objective of this work was to evaluate the ability of soil management systems to change the contents and dynamics of soil carbon. Natural vegetation and systems composed of perennial tropical pastures, annual crops under conventional tillage and no-tillage systems, and pasture rotation with annual crops were evaluated in long-term experiments carried out in Dourados, Maracaju and Campo Grande, Mato Grosso do Sul state, Brazil. The experiments were set in a completely randomized block design, in Dourados and Maracaju, and in a randomized complete block design in Campo Grande. Contents and stocks of total C in soil and in soil organic matter (SOM) fractions were measured. The quality of SOM was estimated by the ratio of C in labile and nonlabile fractions, and expressed in the form of lability. Permanent pasture or pasture in rotation with crops increased C in the particulate fraction and the SOM lability. Lower rates of accumulation and of stocks of soil C were observed in systems explored only with annual crops, while higher values were recorded in systems with pasture.