Conservation tillage effects in the Atlantic Coastal Plain: An APEX examination

Abstract

The Conservation Effects Assessment Project (CEAP) was established to develop a scientific understanding and methodology for estimating environmental benefits and effects of conservation practices on agricultural landscapes at watershed, regional, and national scales. CEAP's goal is to improve the effectiveness of conservation practices and programs by quantifying conservation effects and providing the science and education needed to enrich conservation planning, implementation, management decisions, and policy. Field observations and computer-based simulation of the effects of agricultural conservation are important components of CEAP. This research supports the CEAP effort by utilizing well-documented field data in conjunction with the Agricultural Policy/Environmental eXtender (APEX) model to quantify long-term conservation effects. In this study, field data collected at a research site located near Tifton, Georgia, were used to evaluate APEX and to quantify long-term benefits of implementing conservation tillage in the Atlantic Coastal Plain region of the United States. The objectives of this research were to (1) quantify differences in crop yield, hydrology, and sediment transport for conventional and conservation tillage systems in the Atlantic Coastal Plain; (2) develop a calibrated APEX simulation for these tillage systems; and (3) quantify the performance of the APEX model with respect to crop yields, hydrology, and sediment yield. Fourteen years of crop yield, surface runoff, subsurface flow, and sediment transport data were quantified comparing conventional tillage (CT) to strip tillage (ST). No treatment differences were found for either cotton (Gossypium hirsutum L.) or peanut (Arachis hypogea L.) yields. Surface runoff from the CT was found to be 1.7 times that of the ST, while subsurface flow from the ST was found to be 1.7 times that of CT. Total water loss (surface and subsurface) was nearly equivalent for the two systems: 30% of annual rainfall. Satisfactory model performance was found for APEX surface runoff simulations. Mixed results were found for model performance of crop yield while model simulations of subsurface flow and sediment yield were less than satisfactory. The APEX modeling framework provides a useful tool for assessing crop yield and hydrologic differences between tillage management systems in the Atlantic Coastal Plain. Additional refinement of modeling approaches may be necessary to adequately represent subsurface flow and sediment transport in these same systems.