Dinâmica do carbono influenciada pela qualidade de resíduos culturais, teor inicial de carbono e textura em dois solos subtropicais

Abstract

Crop residues quality and initial soil carbon (C) content influence the residue-derived C dynamic in agricultural soils. However, there is a limited understanding about the fate of residue C and the net C balance in the soil after residues application, particularly in soils subjected to long-term no-till systems. To address this, 13C labeled residues (shoots and roots of soybean and sorghum) were incorporated in soils with different textures and initial soil C content (sand high-C, sand low-C, clay high-C and clay low-C) and incubated in laboratory conditions for 360 days. The C-CO2 e 13C-CO2 were continuously measured and the 13C in remaining residues and in soil were measured after 28, 180 and 360 days. At 360 days, it was performed the size fractionation of soil organic matter (SOM) (<53 μm, 53-250 μm e >250 μm). The residuederived C mineralization was influenced by quality and quantity of residues, initial soil C content, and their interactions. High-C soils provided a greater residue mineralization. After 360 days, the average of mineralized soil organic C (SOC) in soils amended with crop residues was 1.6 greater in high-C than in low-C soils, indicating that SOC cycling is faster in high-C than in low-C soils. On the other hand, high-C content was not determinant to increase the cumulate priming effect (PE) at long-term. Overall, roots induce less PE over time compared to shoot residues, since it also had less residue-C mineralization. The highest PE cumulative was observed in sand low-C soil, which did not show a late negative PE phase as other soils. The residue-derived C recovery was influenced by initial soil C content and residues type interaction, with greater effect of residues quality in low-C than high-C soils, with soybean residues contributed more to soil C than sorghum residues. The roots also included more residue-derived C in the fine fraction in low-C than in high-C soils, while in high-C soils tended show greater residue-derived C recovery in coarse fractions (coarse sand and fine sand). The net C balance showed that amounts of residue-derived C recovery in the soil exceeded the losses of mineralized SOC only in low-C soils. The results show a complex interaction between residues and soil characteristics that affect the new C retention in the soil and the intensity of soil C losses. The high losses of C in high-C soils (reaching to 11% of initial soil C content) and the greater efficiency of residue-C stabilization in low-C soils, highlight the importance of strategies to achieve the residue-C stabilization in subsurface layers of no-till systems.