Submitted to: Agriculture Ecosystems and the Environment
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/2/2008
Publication Date: 6/8/2009
Citation: Udawatta, R.P., Kremer, R.J., Garrett, H.E., Anderson, S.H. 2009. Soil Eenzyme Activities and Physical Properties in a Watershed Managed Under Agrogorestry and Row-Crop Systems. Agriculture Ecosystems and the Environment. 131(1):98-104. Interpretive Summary: Current widely-used soil conservation practices in temperate regions of North America include agroforestry and grass buffer strips. Grass buffers are planted with mixtures of forage or native grasses and legumes in narrow strips on fields following the landscape contour (i.e., perpendicular to slope). As the vegetation establishes on the landscape, runoff and suspended soil contained in runoff are effectively reduced after periods of rainfall. Agroforestry is a multiple-cropping land use system that involves simultaneous production of trees in strips and agricultural crops in alleys between the tree rows. Both grass buffers and trees can diversify production systems by yielding harvests of both forage and tree crops and improving soil carbon storage for ‘carbon credits’ that potentially increase farm profits. Although these conservation systems reduce soil loss, little information is available on the interaction of improved soil properties with biological activity in improving soil quality. Such information can be used to assess the effectiveness of land management practices associated with agroforestry/grass buffer systems. Our objective was to compare selected soil physical properties (soil aggregation, bulk density) with soil carbon and microbiological activities in crop, grass and tree-planted areas in an agroforestry 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. 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 2006 during the corn rotation cycle. Soil samples at 4-in depths were removed from all treatment sites within the watershed in June 2006. Soil carbon and aggregation (measure of soil structure) generally increased simultaneously under grass and agroforestry, suggesting that continuous vegetation was more efficient in improving soil quality by increasing soil organic matter, which stores carbon and contributes to aggregation. Soil enzyme activities, soil quality parameters that indicate levels of nutrient cycling processes important in plant growth, were greater in grass and agroforestry soils compared with soil planted to corn. Higher soil enzyme activities under grass and agroforestry were generally related to improved soil structure detected in these areas, indicated by a greater soil pore network (i.e., porosity) and lower bulk density (measure of compaction), providing better aeration, water infiltration, and improved biological activity compared with soils in the cropped area. Results demonstrated that interaction of physical and biological soil processes contributed to improved soil quality under the soil conservation practices. Results are important to farmers, conservationists, extension personnel, and other scientists because they illustrate the value of conservation management in improving many aspects (physical, chemical, biological) of soil quality on sloping landscapes with potentially erosive soils and that the measurements reported can be easily applied to other areas for assessing soil conservation effects.
Technical Abstract: Soil aggregate stability and diverse microbial activity influence soil quality, crop growth, nutrient retention, water infiltration, and surface runoff. The objective of the study was to test the hypothesis that permanent vegetative buffers improve selected soil physical properties, which contribute to increased microbial enzyme activity. Soil samples (5 cm diam. and 10 cm long) from agroforestry (AG), grass buffer (GB), grass waterway (GWW) and crop (CS) areas were collected from summit, middle, and lower landscape positions at an experimental watershed study near Novelty, MO. Water stable aggregates (> 250µm diam; wet-sieving method), soil carbon, and soil enzyme activity were determined and data were statistically analyzed. Soils under permanent vegetative buffers and GWW had significantly lower bulk density and and higher aggregate stability than the crop areas. Soil carbon contents were highest in the GWW and lowest in the CS treatments. Fluorescein diacetate (FDA) hydrolase, Beta-glucosidase and glucosaminadase enzyme activities were higher in AG, GB, and GWW soils than CS soils. Dehydrogenase activity differed between grass buffer or GWW and crop areas. The results of the study show that aggregate stability, soil carbon, and enzyme activity increased due to establishment of buffers with trees and grass. Increased microbial activity in soils under AG, GB, and GWW management was related to improved soil physical properties (i.e., porosity and macroporosity) suggesting that these conservation practices were effective in improving soil quality.