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United States Department of Agriculture

Agricultural Research Service

Research Project: SOIL ORGANIC MATTER AND NUTRIENT CYCLING TO SUSTAIN AGRICULTURE IN THE SOUTHEASTERN USA
2011 Annual Report


1a.Objectives (from AD-416)
Generally, we are designing crop and animal management strategies based on sound biogeochemical principles, that are profitable, and have positive environmental impacts. Specifically, we are developing strategies based on experiments evaluating tillage and cover crop management, crop selection and productivity, forage quality and availability, plant genetics, grazing pressure, animal health and productivity, animal manure application, nutrient cycling, soil quality, carbon storage, and water runoff and quality.


1b.Approach (from AD-416)
To be able to simultaneously address production and environmental issues, we are taking a multidisciplinary approach to.
1)understand biogeochemical mechanisms and processes involved in water and nutrient cycles,.
2)evaluate alternative management options and.
3)develop management systems to improve the sustainability of agriculture in the region. This requires both field and laboratory investigations, including fescue toxicosis effects on animal physiology. Several field studies will give long-term perspectives and yield realistic relationships between productivity and environmental health cropping studies include:.
1)water catchments receiving poultry litter with different tillage management and.
2)cover cropping trials based on plant species and method and timing of killing. Pasture studies include.
1)evaluation of grazing pressure and organic-inorganic fertilization on soil organic C storage, nutrient runoff, and productivity and.
2)water catchments with differences in endophyte association, organic-inorganic fertilization, and presence of cattle.


3.Progress Report
Laboratory analyses from several long-term field studies and soil testing evaluations continued to be processed and verified. Long-term studies remaining active in this project included the Water Quality Study contributing to our objective of deterimining soil responses in cropping systems and Cattle and Cotton Watershed Study contributing to our objective of determining soil responses in integrated crop-livestock systems. Other field studies that were outlined in the project plan and that had contributed to our objectives were terminated this year due to lack of funds and/or reallocation of resources, including the Dawson Field Grazing Study contributing to our objective of determining soil responses in pasture systems and the Pasture-Crop Rotation Study contributing to our objective of determining soil responses in integrated crop-livestock systems. Additional long-term field studies terminated in previous years due to reallocation of resources included the Silage Cropping Intensity Study to meet our objective in determining soil responses in cropping systems and Salem Road Grazing Study to meet our objective in determining soil responses in pasture systems.

Soil organic carbon content under various cropping, pasture, and pasture-crop rotation systems is being determined and data are contributing significantly to a growing demand for information on how conservation agricultural systems can contribute to the mitigation of greenhouse gas emissions. Scientists involved with this research project are active in assembling original data, reviewing the literature, and synthesizing available information for technical advisors. Scientific advice derived from this project has been offered to the Soil Science Society of America special committees, Cotton Incorporated, Grassland Carbon Working Group associated with the United Nations Food and Agriculture Organization, the World Bank, Technical Working Group on Agricultural Greenhouse Gases, Global Agriculture Climate Assessment, Field to Market: Keystone Alliance for Sustainable Agriculture, and the USDA-NRCS Conservation Effects Assessment Program for Pasture Lands.

This project has been replaced by Project Number 6612-11120-004-00D.


4.Accomplishments
1. Grazing of pastures improves soil condition of degraded land. Sequestration of soil organic carbon and conservation of nitrogen are of keen scientific and political interests for developing management strategies to help combat climate change resulting from emission of common greenhouse gases like carbon dioxide and nitrous oxide. Scientists at the USDA-Agricultural Research Service in Watkinsville, Georgia, conducted a 12-year pasture experiment to investigate how compaction and soil organic matter would be affected by:.
1)inorganic and organic fertilization; and.
2)how forage was utilized. How forage was utilized had an enormous impact on the temporal development of soil properties. When forage was hayed continuously, surface residue was low, soil bulk density was high, and soil organic matter remained relatively unchanged. When forage was grazed by cattle, surface residue was low to moderate, soil bulk density was low to moderate, and soil organic matter was sequestered at high rates. When forage was unharvested (similar to a Conservation Reserve Program management scheme), surface residue was highest, soil bulk density was low (similar to low grazing pressure), and soil organic matter was intermediate between haying and grazing. Cattle grazing of mixed bermudagrass/tall fescue pastures can be considered a viable strategy to rehabilitate millions of acres of degraded cropland in the southeastern USA. Our data negate the perspective that only non-utilization of land will be the best strategy for rehabilitating degraded land.

2. Mechanical aeration captures phosphorus in well-drained soils. Aeration has the potential to reduce phosphorus losses in runoff from grasslands through increased rainfall infiltration, partial incorporation of applied manures, binding of phosphorus with soil minerals, and slowing of runoff flow through increased roughness of the soil surface. Scientists from USDA ARS in Watkinsville, Georgia, University of Tennessee, University of Georgia, and the USDA Natural Resources Conservation Service compiled and reviewed results from two small-plot aeration studies and two field-scale paired watershed aeration studies. Small-scale rainfall simulations were done on two soil taxa using three types of aeration implements. The-field scale studies were conducted in six, 0.7-ha (1.7-acre) bermed field-scale watersheds with varied soil taxa and drainage classes. Small plot studies showed that core aeration reduced total phosphorus (46 %) and dissolved reactive phosphorus (62%) losses from plots fertilized with broiler litter. In the field-scale study, aeration reduced dissolved reactive phosphorus losses by 35% in fields with well-drained soils, but not in poorly-drained soils. In summary, soil characteristics such as internal drainage, depth of the subsoil clayey layer, position of shallow BC horizons, compaction, aeration implement, and type of manure applied on the grassland surface are likely to interact to determine the overall effectiveness of aeration on runoff volume and phosphorus losses.

3. Estimating soil organic carbon with a simple model. Rapid and reliable assessments of the potential of various agricultural management systems to sequester soil organic carbon are needed to promote conservation and help mitigate greenhouse gas emissions. A collaborative effort to calibrate soil conditioning index (SCI) scores against soil organic carbon sequestration was developed among scientists with USDA-Agricultural Research Service in Watkinsville, GA, National University in Asuncion Paraguay, and USDA-Natural Resources Conservation Service in Temple, TX. Published soil organic carbon from long-term field studies throughout the Midwest and southeastern USA were compared with simulations run by the SCI under the umbrella of the Revised Universal Soil Loss Equation (RUSLE2). Across studies, soil organic carbon content increased by 0.435 metric tons of carbon dioxide per acre per year per unit change in SCI. The calibration did not differ significantly between the Midwest and southeastern USA regions. These results will have important implications for farmers, crop advisors, scientists, and policy makers interested in carbon trading schemes throughout the 330 million acres of cropland in the USA.

4. Well-managed pastures sequester soil organic carbon. Soils of the southeastern USA have been historically degraded with intensive cultivation that resulted in loss of topsoil and poor fertility. Pasture management has the potential to build soil fertility, restore soil functions, and mitigate greenhouse gas emissions through surface soil organic matter accumulation. A scientist from the USDA Agricultural Research Service in Watkinsville, Georgia, summarized recent literature from the southeastern USA on how pastures affect soil organic carbon. Establishment of perennial grass pastures in the southeastern USA can sequester soil organic carbon at rates of 0.1 to 0.5 tons carbon/acre/year. Soil organic carbon sequestration rate is affected by forage type, fertilization, forage utilization, animal behavior, and soil sampling depth. It can also be spatially affected by animal behavior and by soil depth. Soil organic carbon storage under pastures is important for improving water relations, fertility, and soil quality. With 111 million acres of agricultural land in the southeastern USA, 113 million tons of carbon dioxide/year could be reasonably calculated as potentially sequestered in soil organic matter. Landowners in the southeastern USA have great potential to restore soil fertility and mitigate greenhouse gas emissions with adoption of and improvement in pasture management systems.

5. Soil carbon is at the core of key ecosystem services. Humans need many things, but unbeknownst to many of us are the intricately critical influences that soil with high organic carbon has on our life support system. Curiously, the growing possibility of trading carbon in a global marketplace may actually help us better appreciate the enormous value of soil carbon on how our world functions and how we have the influence to preserve and enhance critical ecosystem functions or continue to degrade them with reckless abandonment. With the expected rise in human population and the need for even more food to be produced on already stressed landscapes, widespread adoption of conservation agricultural systems is necessary to build a more resilient global food production system that can also help to mitigate climate change and improve our relationship with Nature.

6. Surface-soil organic matter is important determinant of key ecosystem processes. Stratification of soil porosity and organic matter is common under conservation agricultural systems. A scientist at the USDA-Agricultural Research Service prepared a summary of stratification of soil porosity and organic matter for the Encyclopedia of Agrophysics. The volume of soil pores and the concentration of organic matter are greatest nearest the soil surface and decline with depth. This characteristic is typical of undisturbed soils under grassland, forest, and conservation-tilled cropland. The quantity of soil organic matter is important to ecosystem functioning. However, stratification of soil organic matter appears to be even more important to ecosystem functioning. Soil quality and ecosystem functioning could be assessed with calculation of stratification ratio. This article will be useful for undergraduate and graduate students in earth science majors, as well as scientists and an informed public society.


Review Publications
Franzluebbers, A.J., Stuedemann, J.A. 2010. Surface soil changes during 12 years of pasture management in the Southern Piedmont USA. Soil Science Society of America Journal. 74:2131-2141.

Buyer, J.S., Zuberer, D.A., Nichols, K.A., Franzluebbers, A.J. 2010. Soil microbial community function, structure, and glomalin in response to tall fescue endophyte infection. Plant and Soil Journal. DOI: 10.1007/S11104-010-059Z-Y. 339:410-412. 2011.

Franzluebbers, A.J. 2010. Will we allow soil carbon to feed our needs? Scientific and Technical Review. 1:237-251.

Franzluebbers, A.J., Causarano, H.J., Norfleet, M.L. 2011. Soil conditioning index (SCI) and soil organic carbon in the Midwest and southeastern USA. Journal of Soil and Water Conservation Society. 66:178-182.

Last Modified: 9/10/2014
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