Submitted to: Agroforestry Systems
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/31/2011
Publication Date: 4/5/2012
Citation: Paudel, B.R., Udawatta, R., Kremer, R.J., Anderson, S.H. 2012. Soil quality indicator responses to row crop, grazed pasture, and agroforestry buffer management. Agroforestry Systems. 84(2):311-323. Interpretive Summary: Soil conservation practices, designed to reduce soil erosion and improve soil productivity, include establishment of agroforestry systems and grass buffers. Agroforestry is a multiple-cropping land use system that involves simultaneous production of trees and agricultural crops. Grass buffers are composed of forage or native grasses and legumes planted in narrow strips in fields following the landscape contour (i.e., along a constant elevation). Both grass buffers and trees can diversify production systems through harvests of forage and tree crops that potentially increase farm profits. Further, cattle may be included to graze the grassed areas as an important component of a beef or dairy operation. Established vegetation in buffers slows the rate of runoff and filter suspended soil contained in runoff after periods of rainfall. Grazing allows not only the return of organic fertilizer to soil through manure deposition but also may stimulate root growth of grasses thereby improving soil structure. Despite the known benefits in reducing soil loss, little information is available about the effects on biological properties that influence plant productivity and soil quality in these conservation practices. Our objective was to examine changes in soil carbon and nitrogen, soil microbiological activity, and soil structure in agroforestry, grass buffer strip, pasture, and row crop systems established on silt loam soil in the hilly landscape bordering the Missouri River floodplain in central Missouri. In 1999, poplar trees were planted in rows along the landscape contour on 1/4 of the watershed. The adjacent areas comprising 1/2 of the watershed were equally divided to accommodate two treatments: grass buffer strips and pastures with grazing cattle. The crop production area, continuously cultivated under a corn-soybean rotation since 1995, was located on the other 1/4 of the watershed. Soil samples at 4-in depths were removed from all treatment sites within the watershed in June 2009 and 2010. Soil enzyme activities, soil quality parameters that indicate levels of nutrient cycling processes important in plant growth, were greater in grass, pasture and agroforestry soils compared with soil planted to either corn or soybean. Soil carbon and nitrogen contents were lowest for the corn-soybean rotation soil suggesting that soils under continuous vegetation (grass/pasture and agroforestry) are more efficient in improving soil quality by increasing soil organic matter, which stores carbon and nitrogen. Higher soil enzyme activities under grass, pasture and agroforestry correlated with higher stable soil aggregates, which likely provided better aeration, water infiltration, and organic matter stabilization than soils in the cropped area. Results demonstrated that soil conservation practices established with grass and agroforestry buffers greatly improved biological properties of soil quality within the experimental site. The inclusion of cattle for grazing in grass buffers was not detrimental to soil quality and may provide additional economic gains for the farmer. The biological parameters measured in this study differentiated management of soil 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 conservation practices in improving soil quality. The measurements reported can be easily applied to other systems, such as grazing imposed on a soil management practice, for assessing soil conservation effects.
Technical Abstract: Incorporation of trees and establishment of grass buffers within agroecosystems are management practices shown to enhance soil quality. Soil enzyme activities and water stable aggregates (WSA) have been identified as sensitive soil quality indicators to evaluate early responses to soil management. However, few studies exist that compare these parameters among buffers, pastures and row-crop systems. The objective of this study was to examine selected enzyme activities (Beta-glucosidase and Beta-glucosaminidase, fluorescein diacetate hydrolase, dehydrogenase), the proportion of WSA, and soil organic carbon and total nitrogen to assess effects on soil quality under different management systems. The study consisted of four management systems: grazed pasture, agroforestry buffer, grass buffer, and row crop. Two soil depths (0-10 and 10-20 cm) were analyzed for two consecutive years (2009 and 2010). Soil quality indicators were significantly (P<0.05) greater in perennial vegetation compared to row crop. The response of soil quality indicators was consistent in both years. Enzyme activities were significantly (P<0.05) higher than activities detected each year in the row crop system. Surface soil revealed greater enzyme activities and WSA than the sub-surface soil. WSA improved by 17.8 to 31.4 percent in the row crop site from 2009 to 2010 while WSA at the other sites were significantly higher and remained at relatively constant levels at 69.7 to 78.4 percent during the two-year study. Treatment by depth interactions were significant (P<0.05) for Beta-glucosidase and Beta-glucosaminidase in 2009 while the interaction was significant (P<0.05) for dehydrogenase and Beta-glucosaminidase in 2010. Soil enzyme activities were significantly correlated with soil organic carbon (r values up to 0.94, P<0.0001). Higher soil enzyme activities and microbial biomass, enhanced by perennial vegetation, may simultaneously increase other soil quality parameters. Results suggest that understanding effects of management practices on soil quality is important in developing agroecosystems that conserve the soil resource and maintain environmental quality.