Conservation tillage to effectively reduce interrill erodibility of highly-weathered Ultisols

Abstract

Highly weathered Southeastern soils traditionally cropped under conventional tillage systems are drought-prone and susceptible to runoff and soil loss. We quantified differences in infiltration, runoff, soil loss, and interrill erodibilities (K_i) for three soils: Compass loamy sand, Decatur silt loam, and Tifton loamy sand managed under conventional- (CT), strip- (ST), and/or no-till (NT) systems with and without a residue cover (rye [Secale cerale L.]) (+C/-C) and with and without paratilling (+P/-P). Duplicate plots (1 m² [~10 ft²]) on each tillage treatment received simulated rainfall (50 mm h^-1 [2 in hr^-1] for two hours). Runoff and sediment yields were continuously measured, and K_i values were calculated from measured data. The Water Erosion Prediction Project (WEPP) model was used to extend experimental data to long-term annual trends. For the Compass soil, NT-C plots increased runoff by as much as 43% and sediment yields by as much as 10-fold compared to NT+C plots. The NT+P+C plots decreased runoff by as much as 70% and sediment yields by 24-fold compared to CT-P-C. For the Decatur soil, NT+P plots decreased runoff by as much as 71% and sediment yields by as much as 2.7-fold compared to NT-P plots. The NT+P+C plots decreased runoff by as much as 73% and sediment yields by as much as 11.8-fold compared to CT-P-C. For the Tifton soil, ST+P+C plots decreased runoff by as much as 44% and sediment yields by as much as 2.7-fold compared to CT-P-C plots. Calculated K_i values for the Compass, Decatur, and Tifton soils were 0.37, 0.40, and 0.24, respectively. Residue cover decreased effective interrill erodibilities (K_ieff) values by 11%, 2-fold, and 2.6-fold for the Decatur, Tifton, and Compass soils, respectively; Paratilling decreased K_ieff values by 3-fold for the Compass and Decatur soils. The NT and/or ST systems had lower K_ieff values than K_i values from corresponding CT-P-C treatments (Compass = 4- to 37-fold; Decatur = 4- to 13-fold; Tifton = 2-fold). Converting from a CT to a NT or ST system reduced predicted runoff (Compass = 1.7-fold; Decatur = 10% to 17%; Tifton = 1.6- to 2.3-fold) and sediment yields (Compass = 10- to 12-fold; Decatur = 6- to 33-fold; Tifton = 7.3- to 12.1-fold). The most benefit of NT or ST, as quantified by the maximum difference in 100-year predicted runoff and sediment yields, was for the Compass (78%) and Tifton (75%) soils for runoff and for the Compass (10.3-fold) and Decatur soils (9.7-fold) for sediment. Conservation tillage systems (NT, ST) coupled with surface residue cover and/or paratilling are effective in reducing runoff and sediment yields from highly-weathered soils by lowering effective K_i values.