Location: Southeast Watershed Research2017 Annual Report
Objective 1: Quantify reduced soil loss, nutrient, water, and pesticide use efficiencies of best management and conservation practices and devise options for improvements suitable for southeastern cropping systems. Objective 2: Quantify the effects of integrating bioenergy feedstocks into southeastern cropping systems on soil resources and environmental quality and develop options for mitigating adverse effects. Objective 3: Quantify potential benefits and risks of using flue gas desulfurized gypsum with and without broiler litter in southeastern cropping systems to reduce phosphorus loss via runoff.
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.
This new NP 216 bridging project was approved on 6/15/2016. Progress since is captured in the following. The first objective was performed in experimental fields at the University of Georgia Gibbs Farm that primarily was managed under a different projecat (NP 212) and has transitioned to the recently-approved NP 211 project. The new project calls for a new experimental field layout and a period of field recalibration where new fields are treated the same until new research treatments are put in place. This realignment is underway. In the meantime, research work under the previous project progressed as intended except for work on pesticides which has been removed due to the retirement of the SY leading the work. The second objective (effect of integrating bioenergy feedstock into southeastern cropping systems) was also carried out in the experimental fields as those of Objective 1. However, the final bioenergy feedstock crop in the rotation was harvested in 2015. As the next phase will fall in the middle of the realignments period explained above for objective 1, this second objective has been deleted. The integration of bioenergy feedstock in NP 216 will be considered once the realignment of the new field and treatment setup has been completed and the new research initiated. Research activities under objective 3 continue at 30 small plots at Gibbs Farm to assess the impacts of application of flue gas desulfurized gypsum and poultry litter on corn production, soil properties, and phosphorous in runoff. A winter rye cover and summer corn crops were successfully grown and harvested. The rye was rolled and chemically killed before incorporating into the soil by disking. The research is funded through a Trust Fund Cooperative Agreement with Southern Company Inc. and Duke Energy. The overall project involves similar objectives and research activities at two other ARS locations (Auburn, Alabama; Oxford, Mississippi). In Tifton, Georgia, surface runoff samples are obtained from small in-field runoff collectors and surface runoff and nutrient losses characterized. Nutrient analyses were carried out at the University of Florida in Gainesville, Florida. We found their rates to be very competitive compared to University of Georgia in Athens, Georgia, where earlier samples were analyzed. Changes were made to treatments during this reporting period. During the previous three crop seasons, poultry litter and gypsum were applied at a high rate of 6 tons per acre per year to plots and buffer areas downstream of some of the plots. In early spring 2017, soil cores were taken to 3-ft depth from each of the 30 plots and 16 buffer areas and sectioned off into 6 inch lengths to assess soil physical, chemical and biological changes during the high rate of application period. Overall differences in yield and runoff quantity and quality also were assessed for this period. Beginning in April 2017, rates were reduced to 2 tons per acre per year in plots and buffers because 1) these are typical rates producers would apply in fields, and 2) we want to evaluate the changes in the assessed variables at high and typical application rates.
1. Sediment-bound total organic carbon and total organic nitrogen losses higher in conventional versus strip tillage cropping systems. It is essential to quantify the impact of regional crop production systems on carbon and nitrogen cycles to develop best management practices that ensure sustainable food and fiber production, soil fertility, and water quality, and resilience to drought. ARS researchers in Tifton, Georgia, demonstrated that strip tillage and rye winter cover crops retain more soil carbon and nitrogen than when conventional tillage is practiced in a cotton-peanut rotation, in part because of much greater sediment-bound carbon and nitrogen erosion. The reduced sediment losses from strip tillage resulted in increased retention of total organic carbon and nitrogen in surface soil. Observed sediment-bound enrichment ratios for total organic carbon and nitrogen were greater than those in the general literature pointing to the need for additional site-specific research, especially those in sandy soils under hot and humid climates where organic matter may play a greater role in soil fertility.
2. Well-managed grazing systems provide enhanced ecosystem services. Well-managed grazing systems can provide valuable ecosystem services such as reducing sediment and phosphorus loading to nearby waterways but the available long-term data are limited to fully support this hypothesis. ARS researchers in Tifton, Georgia, demonstrated that the concurrence of cattle with hydrologic events that favor transport processes (high rainfall, runoff, and peak flow, etc.) leads to elevated levels of phosphorus delivery to streams. Six large rainfall events accounted for 53% of total phosphorus loss over an 11 year period, and export was exacerbated when a large rainfall event followed a period of drought. Hydrologic transport processes were the dominant drivers of phosphorous flux, and when good grass cover was combined with effective rotational grazing and a planned fertilization strategy, phosphorus loss was <1.0% of fertilizer applied and re-deposited through cattle manure.
3. Conservation management systems incorporating strip tillage (ST) and winter cover crops. Conservation management systems incorporating strip tillage (ST) and winter cover crops may improve soil available nitrogen by more than 27 kg/ha/yr in the sandy landscapes of the southeastern Coastal Plain. Nitrate leaching is an important pathway of dissolved nitrogen loss from the rooting zone in sandy soils of the southeastern Coastal Plain and contributes to surface and ground water contamination as well as higher input costs for producers. ARS researchers in Tifton, Georgia, demonstrated that there were no significant differences in the amount of nitrate leached from the top 15 cm of soils managed under ST (122 kg/ha) versus conventional (rip-and-bed) tillage (CT; 144 kg/ha). However, in context with other nitrogen losses from the region, (surface runoff, 6-8 kg/ha; subsurface flow, 45-99 kg/ha; annual stream nitrogen export, ~5 kg/ha; and crop harvest, 259 and 437 kg/ha for peanuts and cotton, respectively), conservation management may increase soil organic nitrogen storage (27-31 kg/ha/yr) thus reducing overall nitrogen loss. Larger soil organic nitrogen and microbial biomass pools in the conservation systems also suggest improved nitrogen availability for crops.
4. Near-infrared Reflectance Spectroscopic (NIRS) analysis models effective for rapid qualification of forage quality. The use of soybean and sunflower residues as livestock forage has potential as an added source of revenue for organic production systems. ARS researchers from USDA-ARS in Tifton, Georgia, worked with collaborators from University of Georgia to develop and validate NIRS calibration models for organically grown soybean and sunflower that incorporate 27 forage quality parameters commonly used for livestock nutrition management. The results showed that the same model was able to adequately quantify forage quality of both crops even when managed under different tillage treatments and tested at different stages of growth. The models can be reliably applied as a rapid and low cost method for the routine analysis of soybean and sunflower forage quality.
Endale, D.M., Potter, T.L., Strickland, T.C., Bosch, D.D. 2017. Sediment-bound total organic carbon and total organic nitrogen losses from conventional and strip tillage cropping systems. Soil and Tillage Research. 171:25-34. Https://doi:10.1016/j.still.2017.04.004.
Potter, T.L., Coffin, A.W. 2016. Assessing pesticide wet deposition risk within a small agricultural watershed in the Southeastern Coastal Plain (USA). Science of the Total Environment. 580:158-167. doi:10.1016/j.scitotenv.2016.11.020.
Potter, T.L., Bosch, D.D., Strickland, T.C. 2016. Field and laboratory dissipation of the herbicide fomesafen in the southern Atlantic Coastal Plain (USA). Journal of Agricultural and Food Chemistry. 64(25):5156-5163. doi:10.1021/acs.jafc.6b01649.
Endale, D.M., Schomberg, H.H., Fisher, D., Owens, L., Jenkins, M., Bonta, J. 2017. Phosphorus, iron, and aluminum losses in runoff from a rotationally-grazed pasture in Georgia, USA. Transactions of the ASABE. 60(3):861-875. Https://doi:10.13031/trans.12053.