|Parajuli, P -|
|Jayakody, P -|
|Ouyang, Y -|
|Pote, J -|
Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 12, 2012
Publication Date: March 1, 2013
Citation: Parajuli, P.B., Jayakody, P., Sassenrath, G.F., Ouyang, Y., Pote, J.W. 2013. Assessing the impacts of crop-rotation and tillage on crop yields and sediment yield using a modeling approach. Agricultural Water Management. 119:32-42. Interpretive Summary: Traditional agricultural production practices have negatively affected the environment due to poor management of soil and water resources. Alternative cropping practices, such as reduced tillage and crop rotations, can improve the soil and water resources, and simultaneously improve crop yield and economic return to farmers. A collaborative research team of scientists from Mississippi State University and USDA-ARS explored how changes in crop management of tillage and rotation impact the crop yield and sediment yield from the major watershed in the Mississippi Delta, the Big Sunflower River Watershed (BSRW). The team used the Soil and Water Assessment Tool (SWAT) to simulate crop, soil and water parameters within the watershed and compare that with actual stream flow measurements and crop growth and yield measurements. The data demonstrated that the highest corn yields were obtained under conventional tillage production in a corn/soybean rotation, though tillage did not improve the soybean yield in this rotation. The highest sediment yield was found for continuous soybean production using conventional tillage. A maximum cumulative sediment difference of 8 Mg/ha was observed between no-tillage and conventional tillage over a 28 year period of simulation. Farmers continue to modify their cropping systems in response to anticipated return on investment. Improved management practices that enhance the use of water resources can improve the water use efficiency of agricultural crop, reduce the sediment load from the field, and improve overall crop yield. In addition to improving the environment, this will have a significant and direct impact on return to farmers. The results of this study will help to guide watershed crop management and water quality improvement in the BSRW or any other crop dominated watersheds.
Technical Abstract: This study was conducted in the Big Sunflower River Watershed (BSRW), north-west, Mississippi. The watershed has been identified as “impaired waters” under Section 303(d) of the Federal Clean Water Act due to high levels of sediment and total phosphorus. This excess is then transported to the Gulf of Mexico via the Yazoo River, further damaging the nation's water resources. The specific objectives of this study were to assess the impact of three crop-rotations and tillage practices on crop yields and water quality using the Soil and Water Assessment Tool (SWAT) model. The SWAT model was calibrated and validated using monthly stream flow from three spatially distributed USGS gage stations within the BSRW with good to very good performance (coefficient of determination - R2 values from 0.68 to 0.83 and Nash Sutcliffe Efficiency index - NSE values from 0.51 to 0.63). The SWAT model was further calibrated for corn and soybean yields from research fields at Stoneville and validated with yield data from research fields at the Clarksdale experiment stations with fair to excellent statistics (R2 values from 0.43 to 0.59 and NSE values from 0.34 to 0.96). The SWAT model simulation results demonstrated that corn yields were greater for corn under conventional tillage (mean = 9.88 Mg/ha) than no-tillage (mean = 8.81 Mg/ha) in the corn/soybean rotation. However, tillage practices had no effects on soybean yield for the corn/ soybean rotation. Soybean yields under conventional tillage practices showed greater yields (mean = 3.01 Mg/ha) for the soybean after rice rotation than for soybean after corn. Continuous soybean under conventional tillage had the lowest simulated crop yield (mean = 2.07 Mg/ha) and the greatest sediment yield (5.2 Mg/ha) in this study. The cumulative (1981-2009) difference of the sediment yield at the end of the simulation period (2009) indicated a maximum sediment yield difference of about 8 Mg/ha between no-till and conventional tillage practices, with no-till contributing the lowest sediment yield. The cumulative difference of the sediment yield between no-till and conservation till was approximately 2 Mg/ha. The results of this study will help to better understand the impact of management practices on watershed crop management and water quality improvement within the BSRW. This information can be applied to other agricultural watersheds.