Water Wise Sustainable Farming in the Southeast USA: It’s All About the Roots

Abstract:

Sod based crop rotation (SBR) is a relatively new system of practice that incorporates at least 2 years of a perennial grass followed by a peanut and then cotton rotation. After 15 years of research on farm scale sites, this system has been found to have many advantages over conventional 3 year peanut-cotton-cotton rotations. These benefits include: increased profits; dramatic reductions in irrigation demand, fertilizer (N,P) pesticide use, and energy consumption; and, better carbon sequestration potential. The SBR system works primarily due to enhancement of plant root growth and improvement to soil properties. To forecast the water savings potential of sod based rotation, we employ the Soil Water Assessment Tool (SWAT) model to simulate irrigation water demands over a 34 year period (1980-2013). We utilize data from a distributed network of weather stations to represent a range of climate conditions in the Florida, Georgia and Alabama area and data that represent a range of soil physical properties. The only calibration parameter adjusted in SWAT to distinguish between the new and conventional system of farming is rooting depth. Each model result providing 34 years of annual irrigation water requirements was fit to a cumulative probability distribution function to forecast the water savings potential of SBR. Depending upon soil type and weather station location, forecasted water savings using SBR ranged between 20.3 and 33.1 cm during a 10% chance drought year. With over 526,000 ha of irrigated conventional acres in cotton and peanut within the states of Alabama, Florida, Georgia, and South Carolina alone, this equates to a potential water savings of 1.07 billion to 1.74 billion m³ of water in a drought year. The cumulative mitigative effect of this system has yet to be realized through actual application in these states. However, even at low rates of application it is evident that SBR could significantly reduce the negative impacts of irrigation in the Southeast US as well as other locations where row crops grow in humid subtropical climates.