Microbial community diversity in agroforestry and grass vegetative filter strips

Authors: UNGER, IRENE - Westminster College; GOYNE, KEITH - University Of Missouri; Kremer, Robert; Kennedy, Ann

Submitted to: Agroforestry Systems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/7/2012
Publication Date: 4/1/2013
Citation: Unger, I.M., Goyne, K.W., Kremer, R.J., Kennedy, A.C. 2013. Microbial community diversity in agroforestry and grass vegetative filter strips. Agroforestry Systems. 87:395-402.

Interpretive Summary: Current practices widely used in soil conservation include agroforestry and vegetative buffers (or filter strips) designed to reduce soil erosion and improve soil productivity. Vegetative buffers are composed of forage or native grasses and legumes planted in narrow strips in fields following the landscape contour (i.e., perpendicular to slope). Established vegetation in these strips reduces water runoff and filter suspended soil contained in runoff after periods of rainfall. Agroforestry buffers include simultaneous production of trees and grass or agricultural crops. Both grass and agroforestry buffers can diversify production systems through harvests of forage and tree crops that potentially increase farm profits. Despite the known benefits in reducing soil loss, little information is available about the effects of buffer strips on biological properties that influence plant productivity and environmental quality. This information would be valuable in assessing effectiveness of land management practices associated with vegetative/agroforestry buffer systems. Our objective was to examine changes in soil microbiological activity and the soil microbial community structure in vegetative and agroforestry buffers and a row cropping system established on a silt loam within a northeast Missouri watershed. A 10-year stand of pin oak trees in rows is established along the landscape contour on one-half of the watershed; narrow strips (10 to 15 ft wide) of cool-season grasses along the contour planted in the other half in 1997. Permanent grass waterways are located at the outflow of the watershed. The crop production area of the watershed has been continuously cultivated under a corn-soybean rotation since 1991; soils were sampled in 2009 during the soybean rotation cycle. Soil samples at 4-in depths were removed from all treatment sites within the watershed in October 2009. All soil enzyme activities, soil quality parameters that indicate levels of nutrient cycling processes important in plant growth, were greatest in vegetative buffers and one enzyme in agroforestry soils was higher compared with soil planted to soybean. Selected biochemical markers based on microbial cell components were higher for vegetative and agroforestry buffers compared with the soybean soil, suggesting that soils under continuous vegetation (grass and agroforestry) have more diverse microbial communities. Higher soil enzyme activities under grass and agroforestry were related to greater microbial diversity detected in these areas, indicating greater functionality in nutrient cycling, plant growth promotion, and degradation of a wide range of chemical compounds than soils in the cropped area. Results demonstrated that soil conservation practices established with grass and agroforestry buffers significantly improve biological properties of soil quality. The biological parameters measured in this study differentiated soil management under permanent conservation practices from that where intensive row cropping was practiced. Thus, results are important to farmers, conservationists, extension personnel, and other scientists because they illustrate the value of simple conservation practices in improving soil quality and providing ecosystem services such as biodegradation of agrochemicals. The measurements reported here can be easily applied to other areas and management systems for assessing soil conservation effects.

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 among VFS with differing vegetation, and a traditional row-crop system in a maize-soybean rotation. The soil was underlain by a root and water restrictive argillic horizon (i.e., claypan). 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. Microbial functional activity was significantly (P<0.05) higher in the grass VFS soil with 103 and 25 percent greater dehydrogenase and FDA activities, respectively, compared with the cropland soil. Agroforestry VFS soil was 24 percent higher in FDA activity relative to the cropland soil. The PLFA analysis revealed community structural differences that paralleled these functional differences. The agroforestry VFS soil was characterized by significantly (P<0.05) greater proportions of total bacteria, Gram-negative bacteria, anaerobic bacteria and mycorrhizae fungi compared with 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 after VFS establishment. It also enhances our fundamental knowledge regarding soil microbial communities in VFS, which may explain some ecosystem services provided by VFS (e.g., decomposition of organic agrichemicals).