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Title: Conservation tillage, rotations, and cover crop affect soil quality in the Tennessee Valley: Particulate organic matter, organic matter, and microbial biomass

Author
item MOTTA, A.C. - U. FED DO PARANA, BRAZIL
item Reeves, Donald
item BURMESTER, C - AUBURN UNIVERSITY
item FENG, Y - AUBURN UNIVERSITY

Submitted to: Communications in Soil Science and Plant Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/26/2007
Publication Date: 11/1/2007
Citation: Motta, A.V., Reeves, D.W., Burmester, C.H., Feng, Y. 2007. Conservation tillage, rotations, and cover crop affect soil quality in the Tennessee Valley: Particulate organic matter, organic matter, and microbial biomass. Communications in Soil Science and Plant Analysis. 38(19):2831-2847.

Interpretive Summary: Intensive tillage and continuous cultivation of cotton degrades soil quality by increasing erosion and loss of soil organic matter (soil carbon). Producers and agricultural/natural resource technical specialists need information on the impact of management practices like conservation tillage, crop rotation, and cover cropping on soil quality in order to make sound decisions for managing agricultural soils. ARS scientists at the J. Phil Campbell Sr. Natural Resource Conservation Center, Watkinsville, GA and the Soil Dynamics Research Unit in Auburn, AL, cooperated with scientists from Auburn University and the Federal University of Brazil in Paraná, Brazil to determine the impact of conservation tillage, crop rotations, and cover cropping on soil carbon fractions identified with soil quality in a long-term cotton experiment (initiated in 1979) in the Tennessee Valley of northern Alabama. Tillage and crop management systems included conventional and no-tillage continuous cotton with or without a wheat cover crop; and no-tillage cotton rotated with soybean, corn, or double-cropped wheat/soybean. In 2000, the scientists measured total soil carbon, partially decomposed carbon associated with soil tilth, and carbon in microbes that live in the soil. After 21 years, the continuous cotton under conventional tillage contained 10.3 tons of carbon in the top 10-inches of soil, while the cotton grown with a wheat cover crop and no-tillage contained 13.7 tons of carbon. Carbon measured in soil microbes proved a more sensitive indicator (compared to total soil carbon) of management impacts on soil quality, demonstrating effects from tillage, rotation and cropping intensity. The no-tillage cotton double-cropped wheat/soybean system that combined high cropping intensity and crop rotation provided the best overall soil quality. This information can be used by extension specialists, USDA-NRCS, crop consultants, and producers to promote the use sound soil management practices on the 4 million acres of cotton in the Southeast.

Technical Abstract: Monocropping cotton (Gossypium hirsutum L.) with conventional tillage provides little carbon input to soil, increases erosion and promotes rapid oxidation of existing soil organic carbon (SOC). Management practices like conservation tillage, crop rotation, and cover cropping can impact soil carbon, but the integration of all three components has not been studied, especially in the long-term. We evaluated the impact of conservation tillage, crop rotation, and cover cropping on soil quality indicators in a long-term cotton experiment on a Decatur silt loam in the Tennessee Valley of northern Alabama. Rotation treatments were begun with conventional tillage in 1979; select treatments were converted to no-tillage in 1988 or 1995. Treatments included conventional and no-tillage monocropped cotton with or without a wheat (Triticum aestivum L.) cover crop; and no-tillage cotton rotated with soybean [Glycine max (L.) Merr.], corn (Zea mays L.), or double-cropped wheat/soybean. In 2000 we sampled soil to the 24-cm depth for microbial biomass, SOC, and particulate organic carbon (POMc) determinations. Compared to conventional tillage cotton, other treatments accumulated 3.4 to 7.7 Mg ha-1 more SOC to the 24-cm depth. Particulate organic matter C accounted for 29 to 48, and 16 to 22 % of total SOC for the 0-3 and 3-6cm depths, respectively. Tillage had a strong influence on POMc within the 0-3cm depth, but cropping intensity and cover crop did not affect POMc. A large stratification of microbial biomass was observed, varying from 221 to 434 and 63 to 110 mg kg-1 within the 0-3 and 12-24cm depths, respectively. Microbial biomass proved a more sensitive indicator (compared to SOC) of management impacts, demonstrating effects from tillage, rotation and cropping intensity. The no-tillage cotton double-cropped wheat/soybean system that combined high cropping intensity and crop rotation provided the best soil quality.