CARBON STOCK IN SOIL AND ROOTS OF A GRASSLAND AND A SWARD UNDER GRAZING

Abstract

This study was done was to evaluate the effect of animal grazing on organic C storage in soil and roots in a Sorghastrum setosum grassland and a Cynodon nlemfluensis sward. The study was carried out at Campo Anexo General Obligado and EEA INTA Colonia Benítez, in Chaco, Argentina. Soil and root biomass were sampled at four depths: 0-0.1 m, 0.1-0.2 m, 0.2-0.6 m and 0.6-1 m. C in soil was determined by the oxidation of organic matter method, and the C net mass was estimated according to the bulk density at each soil depth. Roots were washed and separated from the soil using sieves, and the samples were oven dried at 65 ºC for dry matter. The C was calculated assuming a 0.45 fraction. The experimental design was a randomized block design with five blocks in the grassland and three in the sward, with two grazing treatments (with and without). Cumulative soil C content up to 1 m depth was 110.1 and 108.61 Mg ha^-1 for the grassland and the sward, respectively, with significant differences (P < 0.05) between layers at 0.2 and 0.6 m at both sites. Soil C content decreased with soil depth, and more than half of the C was found at the first 0.2 m at both sites. Accumulated C in roots was similar at both sites, with significant differences (P < 0.05) between the two extreme strata. The lowest root mass was at 1 m depth, while its higher volume and distribution was up to 0.2 m.