Humic Substances and Chemical Properties of an Acrisol Amended with Vermicomposted Vegetal and Animal Residues
Vermicomposted vegetal and animal residues are rich in nutrients and humic substances and thus can be applied to the soil as a source of functionalized organic matter (OM) and as an alternative to chemical fertilizers. In Southern Brazil, many animal and vegetal residues are easily accessible. Therefore, this study aimed to evaluate alterations in soil chemical properties and OM chemical composition in response to the application of local vermicomposted residues. The vermicomposts of: cattle manure (CM), sheep manure (SM), rice parboiling sludge (PS), CM+PS; SM+PS; CM+food waste (FW); SM+FW; CM+fruit waste (FRW); and SM+FRW were mixed with Acrisol (Argissolo) samples collected at 0.00-0.20 m layer, and the samples were incubated in plastic bags for 182 days. Soil samples without vermicomposts were also incubated (control). Overall, vermicomposts increased soil pH(H2O), exchangeable Ca and available P and K contents. The treatments with CM or SM with FW promoted carbon accumulation in the soil compared to the control, especially as humin. The humic acids of SM and PS were more oxygenated than the others, and oxygenation was apparently associated with aromatic structures. Fulvic acids of CM+PS showed the greatest oxygenation and aliphatic character. The relationship between vermicompost origin (animal or vegetal) and soil properties or OM composition was not clear. Aromaticity degree (H/C) and C/N ratio were similar in fulvic and humic acids, and oxygenation degree (O/C) as well as polarity index [(O+N)/C] were more efficient parameters to distinguish these humic fractions. We concluded that vermicomposts derived from cheap and easily available vegetal and animal residues in Southern Brazil have great potential as alternative fertilizers as well as sources of functionalized OM when applied to the soil, especially vermicomposts of rice parboiling sludge and cattle or sheep manure mixed with food waste.