Influence of soil use on organic carbon and humic substances of an oxisol in tropical systems

Abstract

The conversion of native forests in crop systems affects the equilibrium of the soil organic carbon (SOC). The objective of this study was to evaluate the contents of SOC and humic substances (humin, humic acid, and fulvic acid) in different soil uses in tropical system. The study area was located at Jaboticabal, Sao Paulo state, Brazil. The atropical oxisol was with different soil uses: pasture for 35years; grain production (soybean and maize) under conventional tillage for 35years; no-tillage system, with maize/maize succession; and soybean/maize succession for 20years. Before the no-tillage system, the area was used for grain production under conventional tillage for 15years. The native forest was considered as a reference of natural environment. Soil sampling was performed in each soil use system using a straight shovel from the 0-0.1-m-depth layer. The soil samples were analyzed for organic C, humin, humic acid, and fulvic acid. Contents in the pasture soil showed the greatest recovery capacity of SOC. The high soil disturbance under conventional tillage promoted the greatest decrease of the SOC, humin, and humic acid. Maize residues showed higher contribution for SOC humification in comparison with soybean residues.