Long-Term Soil Carbon Changes After Conversion to Pine from corn in Central Mexico.

The objective of the present study was to estimate the mass of new soil organic carbon (NSOC) following reforestation with Pinus michoacan on agricultural land in central Mexico. Pine plantations were established on agricultural land previously dedicated to corn production. We established paired plots comparing continuous corn versus plots were pine was reestablished. The amount of NSOC was estimated from the changes in composition of C-13 isotope in soil and plant tissue in a chronosequence were pine plantation establishment ranged from 8 to 20 years following corn. The NSOC was estimated using a standard isotope mixing model. Results indicated statistical differences (p≤0.001) in d13C between corn plots and different age of pine plantations. The amount of NSOC from pine was 62 and 18% in the 0-5 and 5-10 cm soil depth after 20 years, respectively. The average mass of NSOC from pine is 11.2 and 2.30 Mg/ha in the 0-5 and 5-10 cm soil depth, respectively. The average annual accumulation rates are 0.561 and 0.11 Mg/ha per year in the top 10 cm soil depth. No NSOC from pine was found at depths greater than 10 cm. The results suggests that C input from pine only influences the top 10 cm of soil following 20 years of pine plantation growth. Additional data from other pine species will be presented that verify the above pattern suggesting that it will take much longer than 20 years of pine growth to influence C dynamics deeper than 10 cm in the soil.