Comparison of Crop Yields, Soil Moisture, and Nitrate Leaching with South Georgia Soils in SWAT at the Field Scale under UGA Checkbook Irrigation

Abstract:

Proper multi-state water allocation can be a complicated matter solve, as is evidenced by the past forty years of conflict between Georgia (GA), Alabama, and Florida over the Apalachicola-Chattahoochee-Flint (ACF) river basin’s water resources. To help stakeholders and researchers understand this basin, the Soil and Water Assessment Tool (SWAT) has been employed to model the hydrology and land use practices in this area, such as cotton and peanut farming. In addition, this area is home to many different types of soils. Soil type and morphology can affect crop yields and nutrient cycling, but how different soils in GA effect crop yields in SWAT has yet to be quantified. Thus, the objective of this study was to use a field scale model to determine the effect of soil types in southwestern GA on crop yields, soil moisture (SM), and nitrate leaching. A SWAT model previously calibrated for a cotton-cotton-peanut rotation in Tifton, GA was used in this study with 30 years of weather data and the most common management practices in GA, including UGA Checkbook method for irrigation. 24 different types of soils covering over 98% of Region V Soil-Water Conservation District (SWCD) in the STATSGO map were selected and integrated into the model. Soil properties from SSURGO were matched to the STATSGO soils and used in this study, allowing for diversity soils to be accounted while also using a more detailed soils database. A multiple comparison analysis of the different soils was run with the native SSURGO Tifton soil used as the control. When under UGA Checkbook Irrigation, crop yields had little response to the different GA soil types tested in this study excepting for one very sandy soil. Overall yields were lower for all GA soils investigated without irrigation, but topsoil had a larger response to soil parameterization. SM for the top layer showed much more variation and all soils were statistically significant different compared to the control. SM tended to decrease as available water content decreased, clay content decreased, and hydraulic conductivity increased. Nitrate leaching is currently being analyzed; however, future research into individual soil parameters effect on yields and SM is needed to better understand the relationship between crop yields and soil properties in SWAT for improved water distribution decisions in the ACF.