ABSTRACT:The cultivation of cover crops intercropped with fruit trees is an alternative to maintain mulch cover between plant rows and increase soil organic carbon (C) stocks. The objective of this study was to evaluate changes in soil total organic C content and labile organic matter fractions in response to cover crop cultivation in an orange orchard. The experiment was performed in the state of Bahia, in a citrus orchard with cultivar 'Pera' orange (Citrus sinensis) at a spacing of 6 × 4 m. A randomized complete block design with three replications was used. The following species were used as cover crops: Brachiaria (Brachiaria decumbes) -BRAQ, pearl millet (Pennisetum glaucum) -MIL, jack bean (Canavalia ensiformis) -JB, blend (50 % each) of jack bean + millet (JB/MIL), and spontaneous vegetation (SPV). The cover crops were broadcast-seeded between the rows of orange trees and mechanically mowed after flowering. Soil sampling at depths of 0.00-0.10, 0.10-0.20, and 0.20-0.40 m was performed in small soil trenches. The total soil organic C (SOC) content, light fraction (LF), and the particulate organic C (POC), and oxidizable organic C fractions were estimated. Total soil organic C content was not significantly changed by the cover crops, indicating low sensitivity in reacting to recent changes in soil organic matter due to management practices. Grasses enabled a greater accumulation of SOC stocks in 0.00-0.40 m compared to all other treatments. Jack bean cultivation increased LF and the most labile oxidizable organic C fraction (F1) in the soil surface and the deepest layer tested. Cover crop cultivation increased labile C in the 0.00-0.10 m layer, which can enhance soil microbial activity and nutrient absorption by the citrus trees. The fractions LF and F1 may be suitable indicators for monitoring changes in soil organic matter content due to changes in soil management practices.

Os microrganismos desempenham papel chave em vários processos importantes, como decomposição da matéria orgânica. A quantificação da atividade microbiana vem sendo utilizada como indicador de alterações e qualidade do solo. O objetivo deste trabalho foi avaliar as alterações microbiológicas em um Latossolo Amarelo Distrocoeso Típico, submetido a diferentes doses do biofertilizante tipo ‘Vairo’. O experimento foi realizado com a variedade de banana ‘BRS Platina’ (AAAB), nas condições climáticas do município de Cruz das Almas-BA. O delineamento experimental utilizado no experimento foi o de blocos casualizados. Os tratamentos consistiram em cinco doses do biofertilizante ‘Vairo’ (0, 100, 180, 280 e 375 mL planta-1 mês-1 ), com dez plantas úteis por tratamento. As análises microbiológicas foram realizadas no Laboratório de Microbiologia pertencente à Embrapa Mandioca e Fruticultura. Foram avaliados os seguintes atributos biológicos: carbono da biomassa microbiana, respiração basal do solo e quociente metabólico. A dose de 166 mL planta-1 maximizou o carbono da biomassa microbiana do solo cultivado com a ‘BRS Platina’.

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