Biomass-C Transport into Soil Carbon Pools in Brazilian Oxisols: A Long Term Incubation Study.

Food production has been impacted the carbon (C) cycles, and its depletion is principal factor of soil degradation. Thus, aims of this study were to assess impact of different biomass-C rates added to the soil on soil respiration and C transport into three soil layers. Samples of Oxisols were collected for 0-20, 20-40 and 40-100 cm layers from several long-term experiments conducted in tropical and subtropical regions, and were incubated for 20 months. The incubation procedure comprised of the input of 0, 5, 10 and 20 g C kg^-1 soil. After 20 months, the highest soil respiration was measured in treatment receiving the highest C-residues inputs for all sites and soil layers. However, the C-CO₂ release was also related to the antecedent SOC concentration (y=41.5x + 4882; R²=0.7***). The highest soil respiration in the control treatment (e.g. 0 g C kg^-1 soil) occurred in Ponta Grossa site because the soil had high clay and C contents. The high rate of soil respiration was observed on the first days after the input of fresh residues. Thus, regular inputs of residues are needed to sustain the microbial activity in soil. The linear relationship between biomass-C addition and SOC concentration was observed for all sites and all depths. Furthermore, the highest SOC accumulation was observed at the 40-100 cm depth, increasing in 1.6, 0.8 and 0.6 g Kg^-1  in 20 months to Londrina, Lucas do Rio Verde and Ponta Grossa respectively, indicating high C deficit, or sink capacity. The data support the conclusion that the high residues input and crop managements are important to increase C input in deep layers, and the strategy has a vast potential to enhance SOC sequestration by managing crops which can add C into deep layers.