Comparing Soil C Stocks from Soil Profile Data Using Four Different Methods

摘要

Soil organic carbon (SOC) concentration differs by depth, soils, and distinct land uses. Different methods have been used to calculate SOC stocks, and here, we used data from 10 pedons from Southern Brazil to compare four methods: horizon values withdiscrete data, exponential function, equal-area exponential function, and equal-area quadratic spline function. SOC stocks were calculated up to 30 cm and 100 cm depth from (i) the original data, (ii) the standardized data based on equal mass, (iii) thestandardized data based on equal mass minus coarse fragments (gravels). Results were compared calculating SOC stocks up to 30 and 100 cm depth. Discrete values by horizon produced mean SOC stocks for 30 and 100 cm depth of 6.9 and 14.6 kg/m2 for originalvalues, 6.5 and 14.1 kg/m2 for standardized values by mass, and 6.3 and 13.5 kg/m2 for standardized values by mass minus gravels. Negative exponential functions produced mean values of 6.1 and 14.1 kg/m2 for original values, 5.6 and 13.3 kg/m2 for standardized values by equal mass, and 5.4 and 12.9 kg/m2 for standardized values by equal mass minus gravels. Equal-area exponential function had mean values of 7.1 and 14.5 kg/m2 for original values, 6.6 and 13.9 kg/m2 for standardized values by equal mass,and 6.4 and 13.5 kg/m2 for standardized values by equal mass minus gravels. Equal-area spline produced SOC averages of 6.8 and 14.7 kg/m2 for original values, 6.3 and 14.2 kg/m2 for standardized values by equal mass, and 6.1 and 13.7 kg/m2 for standardized values by equal mass minus gravels. From the comparison, we found that negative exponential functions produced lower SOC stocks than horizons in the upper layers and higher stocks than horizons in the lower layers; equal-area exponential produced SOCstocks that are statistically similar to horizon values; equal-area spline function produced values up to 30 cm depth statistically similar to horizon values and statistically different up to 100 cm depth. We can conclude that different methods for calculating SOC stocks by depth produce significantly different results and values derived from equal-area exponential and equal-area splines are more similar to those of the horizons.