David B. Marx

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.

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.

Spatial Variations in Nutrient and Microbial Transport from Feedlot Surfaces

Nutrient and microbial transport by runoff may vary at different locations within a beef cattle feedlot. If the areas making the largest contributions to nutrient and microbial transport can be identified, it may be possible to institute site-specific management practices to reduce runoff nutrient and microbial transport. The objectives of this study were to: (1) measure selected feedlot soil properties and nutrient and microbial transport in runoff from various feedlot locations, (2) compare the effects of unconsolidated surface materials (USM) (loose manure pack) and consolidated subsurface materials (CSM) (compacted manure and underlying layers) on nutrient and microbial transport, and (3) determine if nutrient and microbial transport in runoff are correlated to selected feedlot soil characteristics. Simulated rainfall events were applied to 0.75 m wide by 2 m long plots. No significant differences (P < 0.05) in feedlot soil characteristics or nutrient transport in runoff were found between USM and CSM. However, concentrations of E. coli were significantly greater in the USM than the CSM. Pen location was found to significantly influence feedlot soil measurements of Bray-1 P, calcium, chloride, copper, electrical conductivity (EC), loss on ignition, organic N, phosphorus, potassium, sodium, sulfur, total N (TN), water-soluble P, and zinc. Runoff measurements of dissolved phosphorus (DP), EC, and NH4-N were significantly influenced by pen location and were correlated to selected feedlot soil characteristics. Thus, it may be possible to estimate DP, EC, and NH4-N in runoff from selected feedlot soil parameters.

Crop Residue Effects on Runoff Nutrient Concentrations Following Manure Application

Manure is applied to cropland areas managed under diverse conditions, resulting in varying amounts of residue cover. The objective of this study was to measure the effects of crop residue on nutrient concentrations in runoff from areas where beef cattle or swine manure were recently applied but not incorporated. Plots 0.75 m wide by 2 m long were established at the study site. Existing residue materials were removed, and corn, soybean, or winter wheat residue was added at rates of 2, 4, or 8 Mg ha-1. Manure was then applied at rates required to meet estimated annual nitrogen requirements for corn. Control plots with manure but no residue, and plots with no residue and no manure were also established. 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), total phosphorus (TP), NO3-N, NH4-N, total nitrogen, runoff, and soil loss were measured for each rainfall event. When beef cattle or swine manure was applied to plots containing residue materials, nutrient concentrations in runoff were not affected by the amount of crop residue on the soil surface. Concentrations of DP and NO3-N in runoff from the plots with beef cattle manure were significantly greater on the plots with residue than on the no-residue treatments. No significant differences in runoff nutrient concentrations were found between the residue and no-residue treatments with swine manure. Concentrations of DP and TP were significantly less on the no-residue/no-manure treatment than on the plots with beef cattle or swine manure.

NARROW GRASS HEDGE EFFECTS ON NUTRIENT TRANSPORT FOLLOWING COMPOST APPLICATION

The placement of stiff-stemmed grass hedges on the contour along a hillslope has been shown to decrease nutrient transport in runoff. This study was conducted to measure the effectiveness of a narrow grass hedge in reducing runoff nutrient transport from plots with a range of soil nutrient values. Composted beef cattle manure was applied at dry weights of 0, 68, 105, 142, and 178 Mg ha -1 to a silty clay loam soil and then incorporated by disking. Soil samples were collected 243 days later for analysis of water-soluble phosphorus (WSP), Bray and Kurtz No. 1 phosphorus (Bray-1 P), NO3-N, and NH4-N. Three 30 min simulated rainfall events, separated by 24 h intervals, were then applied. The transport of dissolved phosphorus (DP), total P (TP), NO3-N, NH4-N, total nitrogen (TN), runoff, and soil erosion were measured from 0.75 m wide × 4.0 m long plots. Compost application rate significantly affected soil measurements of WSP, Bray-1 P, and NO3-N content. The transport of DP, TP, NO3-N, NH4-N, TN, runoff, and soil erosion was reduced significantly on the plots with a grass hedge. Mean runoff rates on the hedge and no-hedge treatments were 17 and 29 mm, and erosion rates were 0.12 and 1.46 Mg ha -1 , respectively. Compost application rate significantly affected the transport of DP, TP, and NO3-N in runoff. The experimental results indicate that stiff-stemmed grass hedges, planted at selected downslope intervals, can significantly reduce the transport of nutrients in runoff from areas with a range of soil nutrient values.

NUTRIENT TRANSPORT AS AFFECTED BY RATE OF OVERLAND FLOW

Little information is currently available concerning the effects of varying flow rate on nutrient transport by overland flow. The objective of this study was to measure the effects of overland flow rate on nutrient transport following the application of beef cattle or swine manure to plots containing 0, 2, 4, or 8 Mg ha -1 of corn residue. After addition of residue materials to 0.75 m wide by 2.0 m long plots, beef cattle or swine manure was added and the plots were then either disked or maintained in a no-till condition. Three 30 min simulated rainfall events, separated by 24 h intervals, were applied at an intensity of approximately 70 mm h -1 . The transport of dissolved phosphorus (DP), particulate P (PP), total phosphorus (TP), NO3-N, NH4-N, total nitrogen (TN), and soil loss was measured. Nutrient load from the plots on which manure was applied was not significantly affected by the amount of corn residue on the soil surface. Transport of DP in runoff was greater under no-till than till conditions. Rate of overland flow significantly affected PP and TP load. The transport of NO3-N and TN was affected by runoff rate but was not significantly influenced by tillage. Both tillage and runoff rate were found to affect the transport of NH4-N in runoff. Soil loss was significantly influenced by the amount of residue on the soil surface and runoff rate. Tillage condition and runoff rate should be considered when nutrient transport from land application areas is estimated. Keywords. Crop residue, Land application, Manure management, Manure runoff, Nitrogen movement, Nutrient losses, Phosphorus, Runoff, Tillage, Water quality.

Nutrient and Bacterial Transport in Runoff from Soil and Pond Ash Amended Feedlot Surfaces

The addition of pond ash (fly ash that has been placed in evaporative ponds and subsequently dewatered) to feedlot surfaces provides a healthier environment for livestock and economic advantages for the feedlot operator. However, the water quality effects of pond ash amended surfaces are not well understood. The objectives of this field investigation were to: (1)�compare feedlot soil properties, and nutrient and bacterial transport in runoff, from pond ash amended surfaces and soil surfaces; (2) compare the effects of unconsolidated surface materials (USM) (loose manure pack) and consolidated subsurface materials (CSM) (compacted manure and underlying layers) on nutrient and bacterial transport in runoff; and (3) determine if the measured water quality parameters are correlated to soil properties. Simulated rainfall events were applied to 0.75 m wide × 2 m long plots with different surface materials and surface conditions. Measurements of calcium, magnesium, sulfur, and pH were found to be significantly greater on the pond ash amended surfaces. In comparison, the soil surfaces contained significantly greater amounts of Bray 1-P. The runoff load of NH4-N was significantly greater on the pond ash amended surfaces, while the total phosphorus (TP) load was significantly greater on the soil surfaces. The NO3-N and total nitrogen (TN) loads in runoff were significantly greater on the feedlot surfaces containing CSM. Concentrations of E.�coli in runoff were similar on the pond ash amended surfaces and soil surfaces. The dissolved phosphorus (DP), particulate phosphorus (PP), and TP load of runoff were all significantly correlated to Bray 1-P measurements.

NITROGEN AND PHOSPHORUS CONCENTRATIONS OF RUNOFF AS AFFECTED BY MOLDBOARD PLOWING

The excessive application of manure on cropland areas can cause nutrients to accumulate near the soil surface. This study was conducted to measure the effects of moldboard plowing on the redistribution of nutrients within the soil profile and nutrient transport by overland flow. Composted beef cattle manure was applied at dry weights of 0, 68, 105, 142, and 178 Mg ha-1 to a silty clay loam soil and then incorporated by disking. Selected plots were moldboard plowed 244 days later to a depth of approximately 23 cm. Soil samples for analysis of water-soluble phosphorus, Bray and Kurtz No. 1 phosphorus (Bray-1 P), NO3-N, and NH4-N were collected at depths of 0-5, 5-15, and 15-30 cm before and after moldboard plowing. Three 30 min simulated rainfall events, separated by 24 h intervals, were then applied. Dissolved phosphorus (DP), NO3-N, NH4-N, and total nitrogen (TN) content of runoff were measured from 0.75 wide × 2.0 m long plots. Bray-1 P content at the 0-5 cm soil depth was reduced from 200 to 48.0 mg kg-1 and NO3-N content decreased from 9.49 to 2.52 mg kg-1 as a result of the moldboard plowing operation. Consequently, mean concentrations of DP and NO3-N in runoff decreased from 1.76 and 2.29 mg L-1 under no-till conditions to 0.03 and 0.60 mg L-1 on the moldboard plow plots. Thus, the experimental results suggest that moldboard plowing can significantly reduce concentrations of DP and NO3-N in runoff from land application areas.

NARROW GRASS HEDGE CONTROL OF NUTRIENT LOADS FOLLOWING VARIABLE MANURE APPLICATIONS

The effectiveness of a narrow grass hedge in reducing runoff nutrient loads following manure application was examined in this study. Beef cattle manure was applied to 0.75 m wide by 4.0 m long plots established on an Aksarben silty clay loam located in southeast Nebraska. Manure was added at rates required to meet none or the 1, 2, or 4 year nitrogen requirements for corn. Runoff water quality was measured during three 30 min simulated rainfall events. Manure application rate significantly affected dissolved phosphorus (DP) and total phosphorus (TP) loads in runoff on the plots without a grass hedge. However, DP and TP loads were not significantly affected by manure application rate on the plots containing a hedge. The hedge reduced the mean load of DP in runoff from 0.69 to 0.08 kg ha-1 and the load of TP from 1.05 to 0.13 kg ha-1. When averaged across manure application rates, 0.11 kg NO3-N ha-1, 0.02 kg NH4-N ha-1, and 0.49 kg total nitrogen (TN) ha-1 were measured from the plots with a hedge, compared to 0.39 kg NO3-N ha-1, 0.55 kg NH4-N ha-1, and 2.52 kg TN ha-1 from the plots without a hedge. For the plots with a grass hedge, runoff loads of DP and TP where manure was applied were similar to values obtained with no manure application. Each of the runoff water quality parameters was significantly affected by runoff rate. A narrow grass hedge placed on the contour across a hillslope significantly reduced runoff nutrient loads following variable manure applications.

Analysis of an Ion-Selective Electrode Based Methodology for Integrated On-The-Go Mapping of Soil pH, Potassium, and Nitrate Contents

Knowledge of the spatial variation of soil attributes is critical for precision agriculture. On-the-go soil sensors have been able to provide relatively high mapping density while assessing this variation. A new ion-selective electrode (ISE) based approach was developed and tested for simultaneous mapping of soil pH, residual nitrate (NO3-), and soluble potassium (K+) contents. In this article, results of laboratory experiments investigating the effects of key measurement factors on ISE performance are presented. In addition to four different soils, these factors included: soil/water ratio (SWR), quality of water used for electrode rinsing (QWR) and for ion extraction (QWE), presence of ionic strength adjuster (ISA), and solution agitation (stirring). After the targeted ion activity presented by different soils, SWR was the second most influential factor causing increased measurement variance, while the influence of QWE was only significant for pH measurements. Based on this study, the following measurement parameters were recommended: agitated purified water extraction without ISA, addition of a fixed amount of water (preferably 1:1 soil/water ratio), and use of regular (tap) water for electrode rinsing.