Carbon, light organic matter and oxidizable organic carbon fractions | Carbono, matéria orgânica leve e frações oxidáveis do carbono orgânico sob diferentes sistemas de produção orgânica

English. The evaluation of water light organic matter and organic carbon fractioning by different oxidation degrees may contribute to the soil organic matter dynamics understanding in areas under organic management. This study aimed to evaluate the total soil organic carbon (TOC), light organic matter (LOM) in water and TOC oxidizable fractions under different organic production systems. It was selected five areas: fig cultivation, passion fruit and Desmodium sp consortium; corn/beans cultivation in conventional tillage (CT), eggplant/corn cultivation in no-tillage (NT) and agroforest system (AFS). The soil samples were collected at 0-0.05 and 0.05-0.10 m depths, and TOC, LOM in water and organic carbon oxidizable (fractions F1, F2, F3 and F4) were evaluated. The fig area showed higher TOC and N contents. The highest levels of LOM in water were observed in NT and the lowest in CT area. The highest C contents of F1 were observed in fig and passion fruit areas (0-0,05 m). For F4, the Fig and NT areas showed the C highest values (0-0.05 m). In a general way, in the fig area it was observed an increasing of TOC and N contents when compared with others areas. The NT area promot the highest LOM and N contents when compared to the CT system. The organic farming system in no-tillage with eggplant/corn provides better carbon distribution in each oxidizable fraction in relation to the TOC, showing a balance between more lability (F1) soil organic matter and more recalcitrant organic matter fraction (F4).

Portuguese. A avaliação da matéria orgânica leve em água e o fracionamento do carbono orgânico por diferentes graus de oxidação podem contribuir para o entendimento da dinâmica da matéria orgânica do solo em áreas sob manejo orgânico. Este trabalho teve como objetivo avaliar o carbono orgânico total (COT) do solo, a matéria orgânica leve (MOL) em água e frações oxidáveis do COT sob diferentes sistemas de produção orgânica. Foram selecionadas cinco áreas: cultivo de figo, consórcio maracujá - Desmodium sp.; cultivo de milho/feijão, com preparo convencional (PC) do solo; cultivo de berinjela/milho, em sistema plantio direto (SPD) e um sistema agroflorestal (SAF). Foram coletadas amostras de solo nas profundidades de 0-0,05 e 0,05-0,10 m, sendo avaliados o COT, a MOL em água e carbono orgânico oxidável (frações F1, F2, F3 e F4). A área de figo apresentou os maiores teores de COT e N. Os maiores teores de MOL foram observados na área em SPD, sendo os menores verificados na área em PC do solo. Os maiores teores de C da F1 foram encontrados nas áreas de figo e maracujá (0-0,05 m). Para a F4, as áreas de Figo e SPD apresentaram os maiores valores de C (0-0,05 m). De maneira geral, o sistema de uso do solo com figo está aumentando os teores de COT e N em detrimento aos demais. A área sob SPD favorece maiores teores de MOL e N quando comparado ao PC. O cultivo orgânico em sistema plantio direto com berinjela/milho propicia melhor distribuição do carbono de cada fração oxidável em relação ao COT, apresentando um equilíbrio entre matéria orgânica de maior labilidade no solo (F1) e matéria orgânica mais recalcitrante (F4).   Carbon, light organic matter and oxidizable organic carbon fractionsin different organic production systems AbstractThe evaluation of water light organic matter and organic carbon fractioning by different oxidation degrees may contribute to the soil organic matter dynamics understanding in areas under organic management. This study aimed to evaluate the total soil organic carbon (TOC), light organic matter (LOM) in water and TOC oxidizable fractions under different organic production systems. It was selected five areas: fig cultivation, passion fruit and Desmodium sp consortium; corn/beans cultivation in conventional tillage (CT), eggplant/corn cultivation in no-tillage (NT) and agroforest system (AFS). The soil samples were collected at 0-0.05 and 0.05-0.10 m depths, and TOC, LOM in water and organic carbon oxidizable (fractions F1, F2, F3 and F4) were evaluated. The fig area showed higher TOC and N contents. The highest levels of LOM in water were observed in NT and the lowest in CT area. The highest C contents of F1 were observed in fig and passion fruit areas (0-0,05 m). For F4, the Fig and NT areas showed the C highest values (0-0.05 m). In a general way, in the fig area it was observed an increasing of TOC and N contents when compared with others areas. The NT area promot the highest LOM and N contents when compared to the CT system. The organic farming system in no-tillage with eggplant/corn provides better carbon distribution in each oxidizable fraction in relation to the TOC, showing a balance between more lability (F1) soil organic matter and more recalcitrant organic matter fraction (F4).