Dinâmica do carbono orgânico dissolvido em solos com presença de resíduos vegetais

Dissolved organic carbon dynamcis in soils with the presence of crop residues The accumulation of crop residues can increase the soil organic matter content, generating several ecosystem services and are one of the sources for the production of dissolved organic carbon (DOC). The production of DOC in the terrestrial system varies according to the characteristics of the soil, climate and crop. Most soil DOC research has been conducted in forested areas and temperate zones, little is known about DOC in tropical soils. Therefore, a field experiment was conducted with lysimeters with columns of 30 cm of soil to analyze the flow of DOC under soils with contrasting textures: Quartzipsamment (NQ) of sandy texture and Typic Hapludox (LV) of loamy texture, and different plant residues: soybean residue (S) (Glycine max), corn residue (Zea mays) (M), the combination of soybean and corn residues (MS), and without residue (control) (SR). Possible changes in carbon (C) contents and stocks were also evaluated. A total of 64 lysimeters were used, with the treatments: NQ under different plant residues at times three and six months after the beginning of the experiment (totaling 32 lysimeters) and LV under different plant residues at times three and six months after the beginning of the experiment. During the experiment, two destructive collections were made to analyze the layers of 0-10, 10-20 and 20-30 cm, regarding the contents and stocks of C and the water extractable organic carbon (WEOC), representing DOC present in the soil. The first collection was carried out three months after the beginning of the experiment and the second six months after the beginning of the experiment. The lysimeters were subjected to natural rain and the water percolated in the soil was collected for six months, quantified and analyzed for percolated DOC (DOCperc). The results showed that in LV the SR treatment presented a decrease in the C content and stock, S increased the content and stock of C after three months and reduced at the end. The treatments M and MS showed only increase in C content, with the accumulation being greater in MS, because of the variation in the C/N ratio. While in NQ, the mixture of crop residues resulted in a higher consumption of soil organic matter, with a lower accumulation of C than M at the end of the experiment, M showed an increase in C stock and C content in the 0-10 cm layer. In the S treatment, the C content remained constant in the 0-10 cm layer and there was crusting of the surface layer. While the absence of residues led to the formation of a biocrust, with an increase in C content in the 0-10 cm layer and stabilization of the content in the 1020 cm layer in the SR treatment. The WEOC contents and the amount of DOCperc accumulated in NQ did not change under the different residues, with the exception of the WEOC in the 20-30 cm layer, which decreases with time. In LV, the presence of plant residues allowed better soil structuring and greater loss of DOCperc in M and MS, but the DOCperc concentration was the same between treatments. Only the treatment M presented a greater amount of WEOC than SR in the 0-10cm layer. The presence of plant residues affected the dynamic of DOC from the soil.