Grazing Lead to Lower Activities of Carbon-Transforming Enzymes in Soils.

Understanding the impact of cropping systems on carbon-transforming enzymes in soils can provide insight into soil C cycling and contribute to the development of management practices that are ecologically sound and economically viable. Studies were conducted to evaluate the effect of five long-term (>30 years) cropping systems on activities of five carbon-transforming enzymes and to determine the relationship between enzyme activities and basic soil properties. Cropping systems included monocrop soybean (MS), double-crop wheat (for grain)-full season soybean (DC), double crop wheat (for grazing)-early season soybean (GS), and modified double-crop, a two-year rotation including MD1 (early season soybean-winter wheat-full season soybean and MD2 (full season soybean-winter wheat-early season soybean). Soil samples (0–30 cm in 10 cm intervals) were collected and evaluated for pH, content of organic C and total nitrogen (N), and activities of α- and β-glucosidase, α- and β- galactosidase, and β- glucosaminidase. In the surface soils, cropping systems significantly affected the activities of β-glucosidase, α-galactosidase and β-glucosaminidase, but not of α- glucosidase and β- galactosidase. Activities of all tested enzymes were significantly correlated with soil organic C (r=0.74*** ̶ 0.85***) and total N (r=0.70*** ̶ 0.78***), but not with soil pH. Enzyme activities were also significantly inter-correlated, with r values ranging from 0.81*** to 0.94***. Activities of enzymes were found to be in the order of β-Glucosidase activity > β-galactosidase > α-glucosidase > α- galactosidase > β-glucosaminidase. When compared with full season soybean at the sampling year, soils (0-10 cm) planted early season soybean had significantly lower activities of α- galactosidase and β-glucosidase. The activities of the tested enzymes were consistently lower in GS than other cropping systems, suggesting a possible negative impact of grazing on soil’s capacity to cycle nutrients.