Organic-matter lability and carbon-management indexes in agrosylvopasture system on Brazilian savannah

The effect of the introduction of an agrosylvopasture (SASP) system on the changes in the carbon (C) of the soil and its lability were studied. Since 1993, this system has been annually implanted in Paracatu, MG. It was planted under eucalyptus forest abandoned after three cuts, when the brachiaria grass was established. The eucalyptususes were planted at 10 x 4 m spacing, and the following crops have been grown between the lines: rice in the first year, soybean in the second, and brachiaria in the third. After the third year, pasture of the meat cattle begins on brachiaria and remains until the end of the system cycle that was foreseen for the 11th year. A savannah area and another one with eucalyptusus under a conventional system were used as references to natural condition and the way the area is used before plantation of the SASP, respectively. Some samples aged 1, 21 3, 6, and 10 years were collected in SASP. According to the obtained results, the following conclusions were drawn: (i) the C contents and stocks were affected before and during the plantation of the SASP by the use and management of SASP, as they were reduced in the first years of the system establishment but improved at the 10th year; (ii) the C from the particulate free light fraction (CFLLP) that was extracted by potassium pertriangate (KMnO4) was sensitive to the use and management, and so reflected the changes in total organic C (TOC); (iii) the more labile fractions of C that were extracted at different concentrations of sulfuric acid (H2SO4) satisfactorily reflected the changes in both use and management, whereas the less labile fractions were just slightly affected; and (iv) the C management index (IMC) calculated from CFLLP was the most sensitive to the changes in use and management. However, when calculated from the C fraction I extracted by 3M H2SO4 (C-F1), it showed better reliability.