2007 Annual Report 1a.Objectives (from AD-416) 1. Use remote sensing tools to develop rapid assessment procedures for soil and water resources in Coastal Plain agricultural systems. a. Evaluate tillage and residue management effects on soil carbon accretion, soil water content and associated changes in crop response. b. Remotely quantify variability in crop residue cover to better develop indices that may be used to rapidly assess conservation tillage adoption at the watershed scale. 2. Modify, test, and apply the Riparian Ecosystem Management Model (REMM) to evaluate and guide restoration and management of riparian buffers and wetlands. 3. Develop an improved GIS modeling framework for accurately quantifying soil moisture, evapotranspiration (ET), and infiltration in Coastal Plain watersheds. a. Evaluate techniques for assimilating estimates of soil-moisture at the soil surface into field and watershed scale hydrologic models. b. Improve methods for estimating evapotranspiration and infiltration within Coastal Plain watersheds. 4. Evaluate the effects of land use and surface water features on nutrient and dissolved oxygen levels in Coastal Plain watersheds. 1b.Approach (from AD-416) OBJ.1: Direct measurements of soil and plant attributes will be related to crop yield and measurable changes in soil organic carbon accretion, soil water content, plant available water content, microbial community size, soil nitrogen, and nitrate leaching. Remotely sensed data will allow us to. 1)integrate the combined effects of soil organic carbon accretion and nitrogen management via real-time, non-destructive assessments of crop response,. 2)monitor crop response as a function of plant available water and nitrogen contents, and. 3)refine crop coefficients for improved irrigation management and water use efficiency. OBJ.2: The Riparian Ecosystem Management Model will be modified to facilitate use for specific applications such as pesticide transport, P retention estimates, and watershed scale buffer scenario testing. Procedures will be tested for integrating modifications of REMM with watershed scale models. REMM integrations with watershed and channel process models will be tested using watershed data collected at ARS and cooperator watersheds in Georgia, Delaware, Mississippi, Maryland, and elsewhere. OBJ.3: A GIS based modeling system will be developed to simulate soil moisture conditions across the region. Based upon existing soil, climate, and vegetation data, the system will allow point, field, and watershed scale estimates of evapotranspiration, runoff, and soil moisture. It is anticipated that the system will be capable of estimating soil moisture across spatially variable fields for purposes of irrigation scheduling, as well as watersheds equivalent in size to the Little River Experimental Watershed for purposes of long term water resource planning. OBJ.4: Levels of dissolved oxygen will be correlated with other measured water quality parameters for 18 sites in the Suwannee River Basin to determine if relationships exist between dissolved oxygen and stream chemistry. 4.Accomplishments Title: Summer cover crops reduce atrazine leaching to shallow groundwater in southern Florida South Florida's surficial aquifer provides potable water for nearly all of south Florida’s rapidly growing population and agricultural practices, which contribute to water quality impairment, have the potential to adversely affect the massive project focused on restoring south Florida’s Everglades ecosystem. Investigations were conducted in southern Florida to assess risks to groundwater quality from atrazine use for sweet corn production in the region and whether maintaining fields with a highly vigorous cover crop, Sun Hemp [Crotalaria juncea L.], during summer fallow periods would reduce impacts. Results demonstrated that climatic and cropping patterns and relatively high dilution rates in the surficial aquifer combined with high atrazine degradation rates in soil to limit contamination levels compared to other atrazine use sites. Measurements also showed that cover crop use lead to significantly lower contaminant levels in groundwater. Atrazine use presents a small although potential significantly risk to groundwater quality in southern Florida and that use of a cover crop like Sunn Hemp during summer months when fields are fallow may be an effective mitigation measure. Growers are being strongly encouraged to plant cover crops. In addition to reduction in herbicide leaching, there are many other potential benefits, including reduced nutrient leaching and wind erosion and improved soil quality. This research contributes to Problem Area 6, Water Quality Protection Systems of the 201 National Program. 5.Significant Activities that Support Special Target Populations None. 6.Technology Transfer Number of non-peer reviewed presentations and proceedings 3