Impact of conservation land management practices on soil microbial function in an agricultural watershed

Abstract

The USDA Conservation Reserve Program (CRP) involves removing agricultural land from production and replanting with native vegetation for the purpose of reducing agriculture's impact on the environment. In 2002, part of the Beasley Lake watershed in the Mississippi Delta was enrolled in CRP. In addition, areas between the lake and agricultural row crop (RC) fields were established as vegetative buffers (VB) to provide habitat for wildlife. Although the VB were established to improve wildlife habitat, an additional ecosystem service might include serving as an impediment to runoff from adjacent upland areas. The purpose of the current study was to assess the long-term impact of CRP, VB, and RC land management practices on the soil microbial community as an indicator of soil health. Soil samples were collected at two depths (0 to 5 and 5 to 15 cm [0 to 1.97 and 1.97 to 5.91 in]) from 12 sites within each land management (CRP, VB, and RC) area. Samples were assayed for soil enzyme activities (phosphatase, β-glucosidase, N-acetylglucosaminidase [NAGase], and fluorescein diacetate [FDA] hydrolysis) and microbial biomass. All enzyme activities were significantly higher in CRP and VB than in RC soils in the 0 to 5 cm depth. Microbial biomass in 0 to 5 cm soil was higher in CRP than in VB or RC areas. Significant correlations between microbial biomass carbon (C) and the activities of phosphatase (R² = 0.514; p < 0.0001), glucosidase (R² = 0.434; p < 0.0001), and FDA (R² = 0.371; p < 0.0001) were observed, indicating higher extracellular enzyme activities noted in CRP and VB relative to RC soil may be partially due to a larger soil microbial community, although other factors, such as substrate availability, also appear to play a role. The greater size and activity of microbial communities in CRP and VB indicate they are better equipped to process excess nutrients and pesticides and may be a contributing factor to the effectiveness of these conservation practices in reducing the impact of agricultural runoff on downstream bodies of water.