Accumulation of soil organic carbon in Pinus michoacana reforestations

The transfer of stable carbon from vegetation to the soil is an important process for reducing elevated concentrations of atmospheric CO2. The objective of the present study was to calculate the mass of new soil organic carbonic (NSOC) incorporated as a result of the establishment of reforestation with Pinus michoacana. Plots sown with corn were studied, in which a portion of the area was reforested with pine. The amount of NSOC was calculated from the differences in composition of isotopes (delta C-13) from the soil and plant tissue, in a chronosequence, with the simple mixture model. Results indicated statistical differences (p <= 0.001) in delta C-13 between the group of corn plots and the reforestations. The amount of NSOC was 62 and 18%, in the depths of 0-5 and 5-10 cm in reforestations of 20 years. The fit of the data by apparent density and the use of a quadratic model indicated that the average mass of NSOC incorporation is 11.2 and 2.30 Mg ha(-1) at 20 years, and the accumulation rates are 0.561 and 0.11 Mg ha(-1) year(-1) at the same depths. No NSOC from pine was found at depths of over 10 cm, which suggests a higher carbon dynamic in the superficial soil.