Location: Southeast Watershed Research2012 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:
During this first year of the project, we have conducted baseline soil characterizations and established the first crop "Blade" biomass sorghum at the University of Georgia Gibbs Farm (Objective 1). All plots were planted to biomass sorghum in May. The cooperator responsible for mini-rhizotron measurements resigned in February. Root biomass and depth measurements will now be made only annually through soil core collection. Coring will be conducted post-harvest for the biomass sorghum. Nitrogen fertilization rates at the Ponder Farm napier grass biofuels study were increased from 84 to 168 kg N ha-1 (Objective 2). Soil water content continues to be sampled weekly. Soil C and N sampling continues, and root biomass will be measured in 2013. Crop biomass production and C&N content are quantified annually. Fertilizer application at the Shellman napier grass production farm were conducted as scheduled and irrigation regimes have been implemented. Soil cores were collected in April for determination of soil water holding capacity. 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 will be collected on schedule at 45 days after planting. Bases for chambers have been installed at the Ponder Farm and Shellman sites, tested for leaks, and scheduled sampling began in Spring, 2012(objective 3). 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. Soil sampling for determination of pesticide degradation rate will be conducted (Objective 4). Composite surface soil samples (0 to 2 cm depth) were collected from the plot at the top of the slope (plot 7) from both the no-till and conventional-till areas after the field had been prepared for planting and prior to herbicide application. The soil samples were sieved (2 mm), 50-g subsamples placed in incubation bottles, the water content adjusted field capacity, and fortified with atrazine coated on fine sand at the label rate. Bottles were maintained in a laboratory incubator at 25oC with 3 samples remove for analysis on 0,3,7,14,28,42,63, and 100 days after the atrazine treatment. Samples are being analyzed for atrazine and principal soil degradates. Results will be compared to an incubation study conducted in the same way in 2011. This work coincided with the first use of atrazine on these plots in at least 10 years. Findings will help determine if accelerated atrazine degradation conditions will develop following use of this product for weed control.
1. Conservation tillage reduces fine particle sediment erosion and soil carbon loss. Soils in the southeastern U.S. are more susceptible to erosion immediately following soil manipulation at planting. ARS researchers at Tifton, GA demonstrated that long-term strip tillage may increase the proportion of sand sized water stable aggregates in the soil surface compared with conventional tillage, and that conversion from conventional to strip tillage may reduce the potential for soil erosion 3.1 - 4.8 fold; sediment bound carbon loss 3.3 - 5.4 fold; and sediment bound nitrogen loss 2.5 - 4 fold at-planting. Conventional tillage did not alter the amount of carbon in coarse (sand) versus fine (silt + clay) sediment fractions but increased soil carbon loss by increasing the mass of fine particles eroded compared to strip tillage. Results indicate that tillage management in cropping systems at risk for erosion reduce soil carbon and nitrogen losses and maintain fertility.
2. Conservation tillage that includes sunn hemp as a summer cover crop following sweet corn improves the quality of sandy soil. In the humid southeastern U.S., plant residue decomposition rates are very high leaving the sandy soils of the Coastal Plain low in carbon, nitrogen fertility and available water. ARS researchers at Tifton, Georgia demonstrated that inclusion of the tropical legume sunn hemp as a late summer cover crop can increase carbon 43% and nitrogen 68% in the top 2cm of a Tifton loamy sand within three years. This small increase (0.22%) in surface soil carbon increased fertilizer nitrogen use efficiency 10 MgHa-1 compared to fallow cropping systems. Results highlight the critical importance of soil organic matter to maintaining soil fertility of humid southeast cropping systems.
3. Irrigation incorporation and conservation tillage reduce runoff risks of an herbicide used to control glyphosate resistant weeds. A direct consequence of the intense use of the herbicide glyphosate is evolution of glyphosate-resistant populations of several economically damaging weed species. To sustain use of this valuable product and reduce losses growers are advised to rotate and or substitute other herbicides. Some of the most promising for cotton growers in the Southeastern USA are products that contain the active ingredient fomesafen. This active ingredient effectively controls some of the region’s most troublesome weeds. While effective, concerns persist about the potential for fomesafen to be carried into rivers and streams with storm water runoff from treated fields. Researchers of the USDA-ARS Southeast Watershed Research Lab conducted studies to evaluate two mitigation strategies, incorporation with irrigation after herbicide application and use of conservation-tillage. Both practices were found to reduce fomesafen runoff potential by more than 2-fold. Results indicate that these practices should be implemented wherever possible to reduce fomesafen runoff risk.
4. Conservation tillage reduces surface runoff water losses but increases subsurface water losses. While improved infiltration of rainfall into the soil is often observed in conservation tillage systems, hydrologic benefits of reduced tillage systems are often difficult to quantify. Researchers at the USDA-ARS Southeast Watershed Research Laboratory examined eleven years of data from an Atlantic Coastal Plain study site in the Southeastern U.S. and made comparisons of hydrologic responses on conventional and conservation tillage systems. Results indicate that conservation tillage can lead to a 59% reduction in surface runoff. On an annual basis, the reduced surface runoff is offset by a 90% increase in subsurface water losses. However, because little subsurface loss occurs during the summer crop growing season, the conservation tillage system provides beneficial increases in soil water during this critical period of the year.
Strickland, T.C., Potter, T.L., Truman, C.C., Franklin, D.H., Bosch, D.D., Hawkins, G.L. 2012. Results of rainfall simulation to estimate sediment-bound carbon and nitrogen loss from an Atlantic Coastal Plain (USDA) ultisol. Soil and Tillage Research. 122:12-21.