Runoff and nutrient losses from conventional and conservation tillage systems during fixed and variable rate rainfall simulation

Abstract

Tillage systems and fertilizer sources impact soil health and ecosystem services. Rainfall simulations can be used to evaluate tillage and fertilizer management effects on ecosystem services associated with runoff amount and quality. Fixed rate (FR; 57 mm h⁻¹ for 60 minutes) and variable rate (VR; based on the pattern of the most frequent spring rain) simulations were conducted on corn (Zea mays L.) plots supplied with conventional fertilizer (CF; ammonium nitrate [NH₄NO₃]) or poultry litter (PL) and managed with conventional tillage (CT) or no-tillage (NT) on a Cecil soil (Ultisol) near Watkinsville, Georgia. Simulations were conducted in separate years (FR in 2004 and VR in 2005). Tillage and tillage × fertilizer interactions had significant effects on total runoff and sediment loss under FR but not VR. Under FR, 55.8% of the simulated rainfall was partitioned into runoff from CT compared with 9.7% from NT. Under VR, 42% to 60% was partitioned into runoff with no difference among treatments. Sediment loss was 11-fold greater from CT compared with NT under FR (919 g versus 82 g). Under VR, sediment loss varied between 755 g and 2,174 g with no difference among treatments. Tillage and tillage × fertilizer interactions had significant effects on total load for ammonium-nitrogen (NH₄-N) and nitrate-nitrogen (NO₃-N) in both methods and dissolved reactive and total phosphorus (DRP and TP) under VR. Fertilizer source affected loads of NH₄-N under VR and NO₃-N and TP under both methods. Our results confirm that 12 years of continuous NT on a Cecil soil, representative of much of the Southern Piedmont, is far superior to CT for reducing runoff and sediment loss. Larger and more intense storms predicted in future climate projections warrant greater adoption of reduced tillage systems to counteract potential runoff and sediment losses from CT systems.