Moisture seasonality, soil fauna, litter quality and land use as drivers of decomposition in Cerrado soils in SE-Mato Grosso, Brazil

Abstract

In Central Brazil, over one million square kilometers of native savanna vegetation known as Cerrado have been cleared and converted to farmland over the past forty years. A factorial experiment was designed to assess the effects of land use, litter type, soil organisms and season on litter decay in the prevailing natural and agricultural systems (i.e. Cerrado remnants, grasslands and soybean croplands) in Mato Grosso. Decay rates were estimated by using the litterbag method. Two different mesh sizes were used to evaluate the effects of soil macro- and mesofauna (coarse mesh; 5mm) and of soil microorganisms (fine; 20μm). The original litter found in each land use area (Cerrado leaf-litter, Brachiaria-grass or soybean residues) was used to estimate the decay of in situ litter; a standard substrate (maize litter) was employed to evaluate the effect of the environment. Finally, the experiment was carried out during a dry and a rainy season to differentiate the effect of the other factors from the seasonal effect. We found that: (1) the effects of land use and management practice were only significant in the dry season; (2) decomposability of litter was not predicted by the initial C:N ratio of the litter types; (3) soil fauna contributed to the litter breakdown with 13–57%; (4) decay rates were overall higher in the rainy season; (5) all evaluated factors (in following order: season>soil organisms>litter type>land use) and their interactions explained about 70% of the variance in the decay rates in the study area. Change in land use affected litter decay mainly through a shift in the litter quality; the introduced plant species produced highly decomposable litters.