Location: Southeast Watershed Research2013 Annual Report
1a. Objectives (from AD-416):
1. Determine the effects of legume cover crops and soil amendments (e.g., poultry litter and flue gas desulfurization gypsum) on nutrient cycling and other soil processes in cropping systems. 1.1. Quantify the impact of gypsum application on infiltration, runoff, bulk density, soil loss, and soil-water partitioning within the rooting zone on a Tifton soil in a sweet sorghum-peanut-cotton rotation. 1.2. Quantify the impact of gypsum on rooting depth and estimated plant available water in a Tifton soil in a sweet sorghum-peanut-cotton rotation. 1.3. Determine the effect of gypsum on above and below-ground winter cover crop biomass production and associated effects on soil carbon sequestration, summer crop biomass, yield index, and nitrogen use efficiency. 2. Characterize the effects of cropping system, soil management and residue removal rate on soil carbon, specifically how changes in soil carbon storage impact nitrogen use, soil water storage and crop water use, and soil erosion and carbon loss associated with extreme rainfall events. 3. Determine the effects of cropping system, soil management and residue removal rate on the levels and seasonality of trace gas (CO2, CH4, and N2O) emissions. 4. Assess the dissipation, fate, and transport of herbicides and fungicides in soil as a function of soil management and residue removal rate. 4.1. Evaluate pesticide soil persistence including metabolite accumulation and decay as influenced by soil properties, tillage, agronomic amendments, pesticide formulation, and pesticide mode and frequency of application. 4.2. Determine edge-of-field pesticide and degradates loads at the field scale as a function of crop type, gypsum application, and pesticide properties during cotton-sweet sorghum-peanut production with strip- and no-till management.
1b. Approach (from AD-416):
This project will evaluate soil processes in cropping systems that incorporate biomass crops into traditional annual row crop rotations and that facilitate the conversion of idle and marginal agricultural lands to perennial biomass production systems. Goals will be accomplished through provision of: improved data (C&N accretion and cycling rates, water availability and quality effects, evapotranspiration estimates, yield potential and yield indices) for crop production and watershed model calibration; site-specific C and N cycling and trace gas data for the ARS GRACENet database and the Southern Multistate Research Committee’s project S1048; soil quality and hydraulic data that will aid in the development of conservation practice targeting recommendations for sensitive landscape positions within farms and improve hillslope, small watershed, and riparian model parameterizations for Little River Experimental Watershed (LREW); improved understanding of the relationships between crop water use efficiency, soil characteristics (texture, bulk density, carbon content, soil-water holding capacities), and crop biomass production that will facilitate validation of soil water estimation by satellite; and improved information on the effects of conservation practice, future land use, and environmental change scenarios for the southeastern coastal plain region to integrated National Program Assessments’ “what-if” analyses. Emphasis is placed on studies that: 1) define benefits of combining gypsum with conservation-tillage in row crop production systems; 2) use leguminous cover crops to improve the net energy balance of production systems that include biofuels feedstocks; 3) develop guidelines for appropriate nutrient (poultry manure and inorganic fertilizer nitrogen, phosphorus, and potassium) and water amendment rates for perennial grass feedstock production systems; and 4) determine how agronomic and soil management practices impact the fate and soil persistence of herbicides used for control of glyphosate resistant weeds rapidly spreading through Southeastern landscapes.
3. Progress Report:
All analyses for the first cropping year (2012) have been completed at the University of Georgia Gibbs Farm (Obj.1). All plots were planted to peanut in May, 2013 and research is on schedule. Nitrogen fertilization rates at the Ponder Farm napier grass biofuels study were maintained at 168 kg N ha-1 for the 2013 growing season(Obj.2). All objectives intended for the plots have been completed, but the plots are being maintained as a potential site for a soft funds proposal submitted to NIFA. If the proposal is not funded, the plots will be considered for an alternate biofuel crop planting. Fertilizer application at the Shellman napier grass production farm were conducted as scheduled and irrigation regimes have been implemented. Sample analysis is proceeding on schedule. Winter cover harvests and cotton and biomass sorghum plantings were conducted as scheduled at the Sanders-Belflower Farm. Soil fertility samples were collected on schedule at 45 days after planting. GHG sampling at the Ponder Farm and Shellman sites has continued as scheduled (Obj.3). The sampling frequency has been increased to bi-weekly primarily to account for variations in soil moisture and to have a more robust data set to calculate annual rates. The third and final incubation study focused on evaluating atrazine soil dynamics was completed. This study was paired with an examination of aerobic soil dissipation of another symmetrical triazine herbicide, prometyrn (Obj.4). This product has a label for cotton and is considered to have value for control of glyphosate-resistant Palmer Amaranth. Our hypothesis is that organisms that have adapted to atrazine and are responsible for the product’s accelerated dissipation in Tifton soils, will also attack prometyrn and therefore increase its rate of soil dissipation. This would likely reduce efficacy. There implications for herbicide recommendations at Gibbs and regionally for growers who produce sorghum and cotton in rotation. Since atrazine is used extensively on sorghum, the value of using prometryn in cotton crops that follow may be reduced. We expect to complete analyses by the end of September and will prepare a manuscript in the Fall. Soil cores were collected from Gibbs plots to a depth of 1 meter. Cores were sectioned and soil subsamples tested to determine their potential for sulfate adsorption. All subsoils >15 cm were found to be sulfate adsorbing. This indicated that gypsum treatments will likely improve soil quality by reducing subsoil exchangeable Al and increasing soil pH. Deeper rooting of crops into the subsoil is anticipated. Soils subsamples by each depth increment were also sequentially extracted with methanol. Extracts are being screened for residues of active ingredients used on plots and for selected metabolites.
Knoll, J.E., Anderson, W.F., Malik, R., Hubbard, R.K., Strickland, T.C. 2013. Production of napiergrass as a bioenergy feedstock under organic versus inorganic fertilization in the Southeast USA. BioEnergy Research. 6:(3), 974-983. http://link.springer.com/article/10.1007/s12155-013-9328-110.1007/s12155-013-9328-1.