John E. Gilley

RUNOFF AND SOIL LOSS AS AFFECTED BY THE APPLICATION OF MANURE

Manure has been used effectively to improve crop production and soil properties because it contains nutrients and organic matter. While it is generally accepted that the improved soil properties associated with manure application lead to changes in runoff and soil erosion, few studies have quantified these impacts. Water quality models used to assess watershed management and estimate total maximum daily load must accurately predict loading rates from fields where manure has been applied. This study was conducted to assemble and summarize information quantifying the effects of manure application on runoff and soil loss resulting from natural precipitation events, and to develop regression equations relating runoff and soil loss to annual manure application rates. For selected locations at which manure was added annually, runoff was reduced from 2 to 62%, and soil loss decreased from 15 to 65% compared to non-manured sites. Measured runoff and soil loss values were reduced substantially as manure application rates increased. Regression equations were developed relating runoff and soil loss to manure application for rates ranging from 11 to 45 Mg ha –1 , and slope lengths varying from 21 to 24 m. The equations can be used in estimating environmental impacts or to account for manure applications in water quality modeling efforts.

HYDRAULIC CHARACTERISTICS OF RILLS

Rill density and rill flow rates were determined during rainfall simulation tests conducted at 11 sites located throughout the eastern United States. A mean rill density of 1.0 rills/m was found for the study locations. From measurements of the relative distribution of flow rates, a procedure is identified for partitioning flow between individual rills. Regression equations were developed for relating rill width and hydraulic roughness coefficients to flow rate. Equations were also derived for predicting mean flow velocity from visually determined measurements of advance velocity. Information reported in this study can be used to estimate hydraulic characteristics of rills.

Water Erosion Prediction Project (WEPP): Development History, Model Capabilities, and Future Enhancements

The Water Erosion Prediction Project (WEPP) was initiated in August 1985 to develop new-generation water erosion prediction technology for use by federal action agencies involved in soil and water conservation and environmental planning and assessment. Developed by the USDA-ARS as a replacement for empirically based erosion prediction technologies, the WEPP model simulates many of the physical processes important in soil erosion, including infiltration, runoff, raindrop and flow detachment, sediment transport, deposition, plant growth, and residue decomposition. The WEPP project included an extensive field experimental program conducted on cropland, rangeland, and disturbed forest sites to obtain data required to parameterize and test the model. A large team effort at numerous research locations, ARS laboratories, and cooperating land-grant universities was needed to develop this state-of-the-art simulation model. WEPP project participants met frequently to coordinate their efforts. The WEPP model can be used for common hillslope applications or on small watersheds. Because it is physically based, the model has been successfully used in the evaluation of important natural resources issues throughout the U.S. and in many other countries. Upgrades to the modeling system since the 1995 DOS-based release include Microsoft Windows operating system graphical interfaces, web-based interfaces, and integration with Geographic Information Systems. Improvements have been made to the watershed channel and impoundment components, the CLIGEN weather generator, the daily water balance and evapotranspiration routines, and the prediction of subsurface lateral flow along low-permeability soil layers. A combined wind and water erosion prediction system with easily accessible databases and a common interface is planned for the future.

Fate and transport of antimicrobials and antimicrobial resistance genes in soil and runoff following land application of swine manure slurry.

Due to the use of antimicrobials in livestock production, residual antimicrobials and antimicrobial resistance genes (ARGs) could enter the environment following the land application of animal wastes and could further contaminate surface and groundwater. The objective of this study was to determine the effect of various manure land application methods on the fate and transport of antimicrobials and ARGs in soil and runoff following land application of swine manure slurry. Swine manure slurries were obtained from facilities housing pigs that were fed chlortetracyline, tylosin or bacitracin and were land applied via broadcast, incorporation, and injection methods. Three rainfall simulation tests were then performed on amended and control plots. Results show that land application methods had no statistically significant effect on the aqueous concentrations of antimicrobials in runoff. However, among the three application methods tested broadcast resulted in the highest total mass loading of antimicrobials in runoff from the three rainfall simulation tests. The aqueous concentrations of chlortetracyline and tylosin in runoff decreased in consecutive rainfall events, although the trend was only statistically significant for tylosin. For ARGs, broadcast resulted in significantly higher erm genes in runoff than did incorporation and injection methods. In soil, the effects of land application methods on the fate of antimicrobials in top soil were compound specific. No clear trend was observed in the ARG levels in soil, likely because different host cells may respond differently to the soil environments created by various land application methods.

HYDRAULIC ROUGHNESS COEFHCIENTS AS AFFECTED BY RANDOM ROUGHNESS

ABSTRACT Random roughness parameters are used to characterize surface microrelief. In this study, random roughness was determined following six selected tillage operations. Random roughness measurements agreed closely with values reported in the literature. Surface runoff on upland areas is analyzed using hydraulic roughness coefficients. Darcy-Weisbach and Manning hydraulic roughness coefficients were identified in this investigation on each soil surface where random roughness values were determined. Hydraulic roughness coefficients were obtained from measurements of discharge rate and flow velocity. The experimental data were used to derive regression relationships which related Darcy-Weisbach and Manning hydraulic roughness coefficients to random roughness and Reynolds number. Random roughness values available in the literature can be substituted into the regression equations to estimate hydraulic roughness coefficients for a wide range of tillage implements. The accurate prediction of hydraulic roughness coefficients will improve our ability to understand and properly model upland flow hydraulics.

Critical Shear Stress and Critical Flow Rates for Initiation of Rilling

Abstract This study was conducted to identify critical shear stress and critical flow rates required initiate rilling on selected sites. The data used in this investigation were collected from soils located throughout the USA where crop residues had been removed, and moldboard plowing and disking had occurred. Runoff and soil loss measurements were made on sites where simulated rainfall was applied to preformed rills. Multiple regression analyses were used to relate critical shear stress values and critical flow rates to selected soil properties. The soil-based regression equations were found to provide reliable estimates. Information identified in this study will improve our ability to understand and properly model upland runoff and erosion processes.

Runoff and Erosion as Affected by Corn Residue: Part I. Total Losses

THE Effects ofming rates of corn residue on runoff and erosion from a loess soil in southwestern Iowa were measured using a rainfall simulator. Consistent reductions in runoff, sediment concentration and soilloss resulted from increased residue application. Small amounts of surface cover produced substantial reductions in erosion. A regression equation relating surface cover to residue weight was obtained. Equations describing relative runoff, sediment concentration and soil loss as a function of surface cover were also developed using regression analysis.

Interrill Soil Erosion- Part I: Development of Model Equations

ABSTRACT EQUATIONS describing overland flow depth, rainfall induced soil detachment and sediment transport capacity on interrill areas were identified. The Darcy-Weisbach equation which included a parameter for predicting flow resistance caused by rainfall was used to calculate depth of overland flow. Soil detachment was determined from an equation incorporating raindrop induced, impact pressure estimates. The product of a soil transport factor, bottom shear stress and flow velocity was used to calculate sediment transport capacity. Nondimensional forms of the model equations were evaluated using existing experimental data.

LONG–TERM MANURE AND FERTILIZER APPLICATION EFFECTS ON PHOSPHORUS AND NITROGEN IN RUNOFF

Long–term manure and fertilizer applications to a soil can increase phosphorus (P) and nitrogen (N) transport in runoff. This study was conducted to determine P and N transport in runoff following long–term (since 1953) manure and fertilizer applications. Duplicate soil samples (32) were collected in 1998 from the top 0.1 m of selected plots of a long–term manure and fertilizer applications field experiment and later placed in 1 m 2 soil pans in the laboratory. Manure and fertilizer were mixed with 16 of the soil samples, while no treatment was applied to the other half (long–term residual effect). Simulated rainfall was then applied to the soil during initial and wet (24 hours later) events. Manure added just before simulated rainfall resulted in significantly greater concentrations of dissolved P (DP), bioavailable P (BAP), particulate P (PP), total P (TP), NO3–N, and NH4–N than when the last manure application was the previous year in 1997. Soil test P level was not a significant factor in DP loss when manure was applied just before rainfall. When the last manure application was the previous year, similar concentrations of DP, BAP, PP, and TP were measured on the manure and no–manure treatments. Concentrations of NO3–N and NH4–N in runoff were not influenced by long–term fertilizer application, but significantly increased with increasing N application rate when N was applied just before rainfall. Phosphorus concentration in runoff decreased with time of runoff up to 45 minutes, after which the P concentration remained constant. NO3–N and total N concentrations continued to decrease for the entire runoff period. Manure and fertilizer should not be applied when the probability of rainfall immediately following application is great.

NUTRIENT CONCENTRATIONS OF RUNOFF DURING THE YEAR FOLLOWING MANURE APPLICATION

Little information is currently available concerning temporal changes in nutrient transport following the addition of manure to cropland areas. This study was conducted to measure nutrient transport in runoff as affected by tillage and time following the application of beef cattle or swine manure to a site on which corn (Zea mays L.) was grown. Rainfall simulation tests were initiated 4, 32, 62, 123, and 354 days following land application. Three 30 min simulated rainfall events, separated by 24 h intervals, were conducted at an intensity of approximately 70 mm h-1. Dissolved phosphorus (DP), particulate phosphorus (PP), total phosphorus (TP), NO3-N, NH4-N, total nitrogen (TN), electrical conductivity (EC), and pH were measured from 0.75 m wide by 2 m long plots. Concentrations of DP, TP, and NH4-N, in general, declined throughout the year on both the no-till cattle and no-till swine manure treatments. Tillage did not significantly affect concentrations of DP, PP, TP, NH4-N, or pH on the swine manure treatments, but significant variations in these variables were measured over time. Under no-till and tilled conditions on both the cattle and swine manure treatments, the smallest concentrations of DP, NO3-N, NH4-N, and TN occurred on the final test date. The increase in pH of runoff during the study is attributed to the addition of CaCO3 to the rations of beef cattle and swine. Tillage appeared to have less of an impact on runoff nutrient transport from cropland areas than length of time since manure application.