ARS | Publication request: Microbial community diversity in agroforestry and grass vegetative filter strips

Submitted to: Agroforestry Systems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 9, 2012
Publication Date: August 16, 2012
Citation: Unger, I.M., Goyne, K.W., Kennedy, A.C., Kremer, R.J. 2012. Microbial community diversity in agroforestry and grass vegetative filter strips. Agroforestry Systems. 8 Pages.

Interpretive Summary: Land application is a cost-effective method to dispose of animal manure. Manure can contain unmetabolized veterinary antibiotics from livestock feeding and medication. Vegetative filter strips (VFS) may prevent runoff containing these antibiotics from manure-amended fields into surface waters during and after rainfall or irrigation. Vegetative filter strips are land areas of vegetation that provide a buffer between agricultural land and surface water bodies. They have been shown to improve water quality. The antibiotics in runoff water entering the filter strips may adversely affect soil microbial populations and interfere with a diverse biological activity in the root zone necessary to provide long-term treatment. We examined potential differences in soil microbial community characteristics of claypan soil planted to VFS with differing vegetation and a traditional row-crop system in a maize–soybean rotation. The grass VFS soil exhibited the greatest dehydrogenase activity levels and fluorescein diacetate (FDA) activity was greater in the grass and agroforestry (i.e., tree–grass) VFS soils relative to the cropland soil. The agroforestry VFS soil had a greater proportion of total bacteria, gram-negative bacteria, anaerobic bacteria and mycorrhizal fungi than the cropland soil. The grass VFS soil shared some characteristics with the cropland soils; but the grass VFS supported greater mycorrhizal fungi and protozoa populations. These results are important to farmers, soil scientists, soil conservation professionals, and extension personnel because the information provides guidance in proper management and application of livestock manures with minimum impact on soil, air and water quality.

Technical Abstract: Vegetative filter strips (VFS) have long been promoted as a soil conservation practice that yields many additional environmental benefits. Most previous studies have focused primarily on the role of vegetation and/or soil physical properties in these ecosystem services. Few studies have investigated the soil microbial community of VFS. Therefore, we examined potential differences in soil microbial community characteristics of claypan soil planted to VFS with differing vegetation and a traditional row-crop system in a maize–soybean rotation. Samples were tested for soil microbial function and community structure using dehydrogenase and fluorescein diacetate (FDA) hydrolysis enzyme assays and phospholipid fatty acid (PLFA) analysis, respectively. The grass VFS soil exhibited the greatest dehydrogenase activity levels and FDA activity was greater in the grass and agroforestry (i.e., tree–grass) VFS soils relative to the cropland soil. The PLFA analysis revealed community structural differences underlying these functional differences. The agroforestry VFS soil was characterized by a greater proportion of total bacteria, gram-negative bacteria, anaerobic bacteria and mycorrhizal fungi than the cropland soil. The grass VFS soil shared some characteristics with the cropland soils; but the grass VFS supported greater mycorrhizal fungi and protozoa populations. This work highlights differences in soil microbial function and community structure in VFS relative to cropland soil 12 years post VFS establishment. It also enhances our fundamental knowledge regarding soil microorganisms in VFS, which may aid in explaining some ecosystem services provided by VFS (e.g., decomposition of organic agrichemicals).