Methods for assessing the effects of land use changes on carbon stocks of subtropical oxisols

This paper examines a number of calculation methods of soil carbon stocks (CS) to best assess the effects of land use changes in Oxisols and to determine the CS in different agro-ecosystems. The methods were fixed depth (FD), original equivalent soil mass (ESMO), equivalent soil layer (ESL), equivalent soil mass (ESM), fixed mass of 2500 Mg of soil (FM2500), cumulative mass coordinate system (CMC), material coordinate system (SCM), and direct carbon concentrations (CC). The soil sampling was performed in Oxisols in Misiones (Argentina). A randomized complete block design was used with four blocks, and the treatments were subtropical forest (S), tobacco (Nicotiana tabacum L.) (T), satsuma (Citrus unshiu Marc.) (Ci), and yerba mate (Ilex paraguarien-sis St. Hil.) (Y). The soils were clayey, and the variables measured were soil bulk density (BD) and C concentrations. To assess the effect of BD changes on the CS calculated, one simulation was conducted based on averaged data for BD and original carbon situation without disturbance. When the calculation was performed per FD, CS overestimations were found in cultivated soils. Significant differences were observed among CS under different simulated BD situations when using the FD, ESMO, ESM, FM2500, and CMC methods. The ESL and SCM were the most appropriate methods for assessing CS because in the first case, CS are not influenced by changes in BD and in the second case, even if the CS has been slightly modified because of changes in the BD, it was more sensitive to changes in land use. Soils cultivation resulted in a 23 to 36% C loss as compared with the original CS, when the SCM was applied.