Enzymatic activity, microbial biomass, and organic carbon of Entisols from Brazilian tropical dry forest and annual and perennial crops

The conversion of native forests into intensive agricultural cropping affects soil quality and ecosystem functionality in tropical dry areas. Although many indicators have been used to assess soil quality, the most sensitive indicators are biochemical attributes. Absolute enzymatic activity (fluorescein diacetate hydrolysis, dehydrogenase, β-glucosidase, urease, arylsulfatase, and acid and alkaline phosphatases), soil organic C (SOC), microbial biomass C (MBC), and specific enzymes per unit of SOC and MBC were measured in forests and perennial (tomato, pangola grass, cotton passion fruit, and cashew nuts) and annual (bean, cabbage, pigeon pea, and fennel) crops. The changes in soils covered with perennial crops differed from those covered with annual crops as regards biochemical soil attributes. The multivariate analysis grouped the Entisols covered with annual crops far from the forest soils, which indicated that intensive management results in drastic changes in the biochemical quality of Entisols in tropical dry areas. The absolute β-glucosidase activity varied from 18.3 to 100.6 μg p-nitrophenol g^-1 soil h^-1. The tomato areas showed higher dehydrogenase activity with a value of 181.5 μL H g^-1 soil. The absolute β-glucosidase, arylsulfatase, and alkaline phosphatase activity and the specific fluorescein diacetate hydrolysis/SOC, β-glucosidase/SOC, arylsulfatase/SOC, acid phosphatase/SOC, β-glucosidase/MBC, and acid phosphatase/MBC can be used as quality indicators of Entisols cultivated with perennial and annual crops. In addition, pasture soil could have a similar biochemical quality as forest soils in tropical dry areas.

Keywords
Cropping systems; Entisols; soil organic carbon; specific enzyme activity per unit of soil organic carbon.