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United States Department of Agriculture

Agricultural Research Service

Title: Variable Rainfall Intensity and Tillage Effects on Runoff, Sediment, and Carbon Losses from a Loamy Sand under Simulated Rainfall

Authors
item Truman, Clinton
item Strickland, Timothy
item Potter, Thomas
item Franklin, Dorcas
item Bosch, David
item Bednarz, C - UGA - TIFTON

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 19, 2006
Publication Date: August 1, 2007
Citation: Truman, C.C., Strickland, T.C., Potter, T.L., Franklin, D.H., Bosch, D.D., Bednarz, C. 2007. Variable rainfall intensity and tillage effects on runoff, sediment, and carbon losses from a loamy sand under simulated rainfall. Journal of Environmental Quality. 36:1495-1502.

Interpretive Summary: The low-carbon, intensively cropped Coastal Plain soils of Georgia are susceptible to runoff, erosion, and drought. Reduced tillage systems offer a best management tool for sustained row crop production. We compared constant (Ic) and variable (Iv) rate rainfall intensity simulations to evaluate differences in runoff (R), sediment (E), and carbon (C) losses from a Tifton loamy sand cropped to cotton and managed under conventional- (CT) and strip-till (ST) systems. The Iv pattern represented the most frequent occurring intensity pattern for spring storms in the region. Compared to CT, ST decreased R by 2.5-fold, E by 3.5-fold, and C losses by 7-fold; and increased surface soil organic C by 20%. Maximum runoff for Iv events was 1.6 times greater than for Ic events. Total sediment loss for Iv events were 19-36% greater than that for Ic events. Maximum sediment loss rates were ~ 3 times greater than those for Ic events. Total carbon loss values for Iv events were 1.5 times greater than those for Ic events and maximum carbon loss rates for Iv events were 4 times greater than those for Ic events. Tillage effects on runoff, sediment and carbon loss were greater than rainfall intensity effects. Carbon enrichment ratios (CERs) mostly were at or below 1.0 for the ST treatment and at or above 1.0 for the CT treatment. Maximum CER for CT-Ic, CT-Iv, ST-Ic, and ST-Iv was 2.0, 2.2, 1.0, and 1.2, respectively. Our results suggest that strip tillage increases rainfall infiltration into the soil and decreases transport of sediment, carbon, and commonly used agrichemicals as compared to conventioanl tillage. Results also suggest that the processes controlling water storage and sediment and carbon losses from soil would be better understood if variable rainfall intensity patterns derived from natural rainfall were utilized in rainfall simulation studies to evaluate their fate and transport from CT and ST systems. GRACEnet Publication.

Technical Abstract: The low-carbon, intensively cropped Coastal Plain soils of Georgia are susceptible to runoff, erosion, and drought. Reduced tillage systems offer a best management tool for sustained row crop production. Simulated rainfall, with constant rate rainfall intensity, has been used to evaluate relative differences in runoff, sediment, and chemical losses from conventional and reduced tillage systems. Understanding and comparing these losses from different tillage systems could be improved if the effect of variable rainfall intensity during a storm was quantified. Our objective was to quantify and compare effects of constant (Ic) and variable (Iv) rainfall intensity patterns on runoff (R), sediment (E), and carbon (C) losses from a Tifton loamy sand (Plinthic Kandiudult) cropped to cotton (Gossypium hirsutum L.), and managed under conventional- (CT) and strip-till (ST) systems. Four treatment combinations were evaluated: CT-Ic, CT-Iv, ST-Ic, and ST-Iv, each replicated three times. Field plots (12), each 2-m wide by 3-m long, were established on each tillage-intensity treatment. Each 6-m2 field plot received simulated rainfall at a constant (57 mm h-1) or variable rainfall intensity pattern for 70 min (12-run ave.=1402 mL; cv=3%). The Iv pattern represented the most frequent occurring intensity pattern for spring storms in the region. Compared to CT, ST decreased R by 2.5-fold, E by 3.5-fold, and C losses by 7 times; increased soil organic C by 20%. Rmax values for Iv events were 1.6 times greater than those for Ic events, with Rmax for Iv events occurring 38 min before corresponding values for Ic events. Etot values for Iv events were 19-36% greater than that for Ic events. Emax values for Iv events were ~ 3 times greater than those for Ic events, and time to Emax (tEmax) for Iv events occurred 4-11 min before that for Ic events. Tillage effects on R and E were greater than rainfall intensity effects. Ctot values for Iv events were 1.5 times greater than those for Ic events. Cmax values for Iv events were 4 times greater than those for Ic events, with time to Cmax for Iv events occurring 18-23 min before corresponding values for Ic events. During the first 35 min (0-35 min), more R (34-37%), E (37-43%), and sediment-transported C losses (55-57%) occurred from Iv events than from Ic events. Conversely, during the last 35 min (35-70 min), more R (same percentages), E, and sediment-tranported C losses occurred from Ic events than from Iv events. Carbon enrichment ratios (CERs) mostly were at or below 1.0 for the ST treatment and at or above 1.0 for the CT treatment (except for first 20 min). Maximum CER for CT-Ic, CT-Iv, ST-Ic, and ST-Iv was 2.0, 2.2, 1.0, and 1.2, respectively. Partitioning, entrainment, enrichment, and transport of sediment, carbon, and commonly used agrichemicals would be better understood if variable rainfall intensity patterns derived from natural rainfall were utilized in rainfall simulation studies to evaluate their fate and transport from CT and ST systems.

Last Modified: 10/1/2014
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