Dwayne R. Edwards

A PORTABLE RAINFALL SIMULATOR FOR PLOT–SCALE RUNOFF STUDIES

Rainfall simulators have a long history of successful use in both laboratory and field investigations. Many plot–scale simulators, however, have been difficult to operate and transport in the field, especially in remote locations where water or electricity is unavailable. This article describes a new rainfall simulator that is relatively easy to operate and transport to and from the field while maintaining critical intensity, distribution, and energy characteristics of natural rainfall. The simulator frame is constructed from lightweight aluminum pipe with a single 50 WSQ nozzle centered at a height of 3 m (9.8 ft). An operating nozzle pressure of 28 kPa (4.1 psi) yields continuous flow at an intensity of 70 mm h –1 (2.8 in. h –1 ) over a 1.5– U 2–m (4.9– U 6.6–ft) plot area with a coefficient of uniformity of 93%. Kinetic energy of the rainfall is about 25 J m –2 mm –1 (142.8 ft–lb ft –2 in. –1 ), approximately 87% of natural rainfall. The simulator can be easily transported by two field personnel and completely assembled or disassembled in approximately 10 min. Water usage is at a minimum as the simulator utilizes only one nozzle.

Effectiveness of Vegetative Filter Strips in Retaining Surface-applied Swine Manure Constituents

Simulated rainfall was used to evaluate the effectiveness of vegetative filter strips (VFS) of varying lengths (0, 3, 6, 9, 15, and 21 m) in reducing sediment and nutrient losses from plots treated with liquid swine manure at 200 kg N/ha. Mass transport of ammonia nitrogen (NH3-N), total Kjeldahl nitrogen (TKN), ortho-phosphorus (PO4-P), total phosphorus (TP), and total suspended solids (TSS) was reduced significantly (p < 0.05) by fescue (Festuca arundinacea Schreb.) VFS. The 3 and 21 m VFS removed 65 and 87% of incoming TKN, 71 and 99% of incoming NH3-N, 65 and 94% of incoming PO4-P, and 67 and 92% of the incoming TP, respectively. Effectiveness of VFS, however, did not increase significantly beyond 3 m for TSS and chemical oxygen demand and averaged 61 and 50%, respectively. Mass transport of TKN, NH3-N, PO4-P, and TP was minimized at the 9 m VFS length. The VFS did not significantly reduce nitrate nitrogen and fecal coliform from the incoming runoff. First-order kinetics described the removal of manure constituents.

VEGETATED FILTER STRIP REMOVAL OF CATTLE MANURE CONSTITUENTS IN RUNOFF

Pasture runoff can contribute to elevated concentrations of nutrients, solids, and bacteria in downstream waters. The objective of this study was to determine the effects of vegetative filter strip (VFS) length on concentrations and transport of nitrogen, phosphorus, solids and fecal coliform in runoff from plots treated with cattle manure. Three plots with dimensions of 2.4 ×30.5 m were used. The upper 12.2 m of each plot was treated with cattle manure, while the lower 18.3 m acted as a VFS. Runoff produced by rainfall simulators was sampled at VFS lengths of 0, 6.1, 12.2, and 18.3 m and analyzed for total Kjeldahl nitrogen (N), ammonia N, nitrate N, total phosphorus (P), ortho-P, fecal coliforms, total suspended solids and other parameters. The VFS significantly reduced concentrations and mass transport of incoming solids, fecal coliform, and most nutrient forms, particularly P. The relationships among VFS length, concentration and mass transport were well-represented by first-order exponential decay functions. Approximately 75% of incoming total Kjeldahl N, total P, ortho-P, and total suspended solids was removed within the first 6.1 m of the filter strips. Runoff concentrations of fecal coliform concentrations entering the filter strips were as high as 2 ×107 FC/100 mL; after a filter length of 6.1 m, however, the runoff exhibited no measurable concentration of fecal coliforms. This experiment suggests that even relatively short filter strips can markedly improve quality of runoff from grassed areas receiving cattle manure.

Effectiveness of Vegetative Filter Strips in Controlling Losses of Surface-applied Poultry Litter Constituents

Vegetative filter strips (VFS) have been shown to have high potential for reducing nonpoint source pollution from cultivated agricultural source areas, but information from uncultivated source areas amended with poultry litter is limited. Simulated rainfall was used in analyzing effects of VFS length (0, 3.1, 6.1, 9.2, 15.2, and 21.4 m) on quality of runoff from fescue (Festuca arundinacea Schreb.) plots (1.5 ¥ 24.4 m) amended with poultry litter (5 Mg/ha). The VFS reduced mass transport of ammonia-nitrogen (NH3-N), total Kjeldahl nitrogen (TKN), ortho-phosphorus (PO4-P), total phosphorus (TP), chemical oxygen demand (COD), and total suspended solids (TSS). Mass transport of TKN, NH3-N, TP, and PO4-P were reduced by averages of 39, 47, 40, and 39%, respectively, by 3.1 m VFS and by 81, 98, 91, and 90%, respectively, by 21.4 m VFS. Effectiveness of VFS in terms of mass transport reduction was unchanged, however, beyond 3.1 m length for TSS and COD and averaged 35 and 51%, respectively. The VFS were ineffective in removing nitrate-nitrogen from the incoming runoff. Removal of litter constituents was described very well (r2 = 0.70 to 0.94) by a first-order relationship between constituent removal and VFS length.

A Microcomputer-Based Irrigation Scheduler for the Humid Mid-South Region

This article presents the development and field validation of the University of Arkansas Irrigation Scheduler, a microcomputer based program designed to assist in scheduling irrigations in the humid Mid-South. The program has separate subroutines for stationary and towable center pivot systems, and surface (furrow and flood) irrigation systems. The program is designed to schedule irrigations for a system, thus, the water source is the focal point not each individual field served by the water source. Algorithms are incorporated into the center pivot programs to optimize scheduling based on soil moisture considerations as well as tactical goals concerning pivot placement. The program supports irrigation scheduling for soybeans, cotton, corn, and grain sorghum. The user input necessary is daily maximum temperature, daily precipitation and irrigation dates and, for pivot systems, irrigation application depths. The results of several years of field use, in both qualitative and quantitative analyses, indicate that the program is a valuable irrigation scheduling tool for use in the humid Mid-South.

Performance of Vegetative Filter Strips with Varying Pollutant Source and Filter Strip Lengths

Vegetative filter strips (VFS) can reduce runoff losses of pollutants such as nitrogen (N) and phosphorus (P) from land areas treated with fertilizers. While VFS effectiveness is considered to depend on lengths of pollutant source and VFS areas, there is little experimental evidence of this dependence, particularly when the pollutant source is manure-treated pasture. This study assessed the effects of pollutant source area (fescue pasture treated with poultry litter) length and VFS (fescue pasture) length on VFS removal of nitrate N (NO3-N), ammonia N (NH3-N), total Kjeldahl N (TKN), ortho-P (PO4-P), total P (TP), total organic carbon (TOC), total suspended solids (TSS), and fecal coliform (FC) from incoming runoff. This research examined poultry litter-treated lengths of 6.1, 12.2, and 18.3 m, with corresponding VFS lengths of up to 18.3 m, 12.2 m, and 6.1 m, respectively. Runoff was produced from simulated rainfall applied to both the litter-treated and VFS areas at 50 mm/h for 1 h of runoff. Pollutant concentrations in runoff were unaffected by litter-treated length but demonstrated a first-order exponential decline with increasing VFS length except for TSS and FC. Runoff mass transport of NH3-N,TKN, PO4-P, TP and TOC increased with increasing litter-treated length (due to increased runoff) and decreased (approximately first-order exponential decline) with increasing VFS length when affected by VFS length. Effectiveness of the VFS in terms of NH3-N, TKN, PO4-P, TP and TOC removal from runoff ranged from 12-75, 22-67, 22-82, 21-66, and 8-30% respectively. The data from this study can help in developing and testing models that simulate VFS performance and thus aid in the design of VFS installed downslope of pasture areas treated with animal manure.

SUITABILITY OF A GPS COLLAR FOR GRAZING STUDIES

The traditional means of tracking animal location in a field is by visual observation. Not only is this method labor intensive, it is also prone to error as the observer can alter cattle movement, observation periods are often too short to obtain confidence in general daily behavior patterns, and observer fatigue becomes an issue. In the 1990s, the University of Kentucky began using GPS collars on cattle to track their position with the goal of incorporating this information into cattle management practices. One of the key unanswered questions regarding the GPS collars is the accuracy of the position data recorded by the collar. The objective of this work was to assess the capabilities and limitations of using GPS collars to track animal movement in grazed watersheds. Static tests were conducted in an open field, under trees, and near fence lines to ascertain the impacts of various field features on collar performance. Dynamic tests were carried out to examine the errors associated with the collars while operated under real-world conditions. Results from these tests indicate that the collars generally provide data with horizontal accuracies of 4 to 5 m. This information will assist researchers in the development of experiments based on collar capabilities and limitations.

QUALITY OF RUNOFF FROM PLOTS TREATED WITH MUNICIPAL SLUDGE AND HORSE BEDDING

Land application of horse stall bedding and municipal sludge can increase runoff concentrations of nutrients, organic matter, and bacteria as well as steroidal hormones such as estrogen. Concentrations of materials in runoff from sites treated with animal manure can be reduced by aluminum sulfate, or alum [Al2(SO4)3•14H2O] treatment. The objectives of this study were to assess plots treated with horse stall bedding or municipal sludge for: (a) runoff quality [concentrations of nitrate nitrogen (NO3-N), ammonia nitrogen (NH3-N), orthophosphate-phosphorus (PO4-P), fecal coliform (FC), chemical oxygen demand (COD) and 17- sestradiol (17 s-E, a form of estrogen)]; (b) changes in runoff quality caused by alum treatment; and (c) time variations in concentrations of the analysis parameters. Horse bedding and municipal sludge were applied to twelve 2.4 ×6.1 m fescue plots (six each for the bedding and sludge). Three of the bedding-treated and three of the sludge-treated plots were also treated with alum. Simulated rainfall (64 mm/h) was applied to the 12 treated plots and to three control (no treatment) plots. The data were analyzed as originating from separate completely randomized, one-way designs with three replications of each treatment. The first design had treatment levels of bedding, bedding and sludge, and control, while the second design had treatment levels of sludge, sludge and alum, and control. The control data were common to both designs. The first 0.5 h runoff was sampled and analyzed for the parameters described above. Analysis parameter concentrations for the waste treated plots were generally lower than those previously reported for runoff after organic treatments. In some cases, concentrations were no different from the controls. Mass losses of all parameters were low and agronomically insignificant. Alum addition decreased runoff PO4-P concentrations and increased NO3-N concentrations but had no effect on concentrations of other parameters. A significant effect of alum addition on 17 s-E and COD concentrations was anticipated on the basis of previous studies; its absence might have been due to inadequate mixing or interval between addition and simulated rainfall. Relationships between concentration and collection time followed two patterns: (a) highest concentrations occurring during the first sample (two minutes following runoff initiation; NO3-N, COD, FC and 17 s-E) and (b) delay in peak concentration until four minutes following runoff initiation (NH3-N and PO4-P). The detection of different general relationships between concentration and time suggests that different mechanisms are dominant in transport of the parameters analyzed.

Effect of Extractable Soil Surface Phosphorus on Runoff Water Quality

Phosphorus (P) additions to surface water from agricultural nonpoint sources are of concern, because P often limits eutrophication of surface waters. Numerous sources of runoff P exist: indigenous soil and plant material, land-applied manure and sludge, and commercial fertilizer. In many soils receiving commercial fertilizer and manure, concentrations of P at the soil surface have been steadily rising due to either long-term or excessive applications of P. Critical levels of soil surface P may exist, above which runoff may promote eutrophication. Methods for rationally identifying these critical levels are needed to manage losses of P, which implies the need for accurate methods of relating soil surface P concentration (Ps) to runoff P concentration. A study was conducted on both pasture and tilled plots (with and without residue) to evaluate the relationship between Ps and dissolved reactive P in runoff (PR) using simulated rainfall. The data indicated that even for comparable storms, Ps alone was not a satisfactory estimator of PR. A model describing the kinetics of P release from surface soil to runoff was used to include additional variables in predicting PR. When used with uncalibrated parameters, the model explained a significant proportion of the variation in observed PR values for pasture plots (r2 = 0.43) but was less successful in predicting PR for tilled plots (with and without residue, r2 = 0.13). Calibration of (adjustments to) the extraction coefficients resulted in an overall coefficient of determination between observed and predicted PR values of 0.73. While the model was successful in describing how PR and the independent variables are related for the pasture plots, the extraction coefficients should be calibrated to obtain best estimates of PR. When used with calibrated extraction coefficients, the model provided realistic estimates of PR over the range of experimental conditions.

VEGETATIVE FILTER STRIP REMOVAL OF METALS IN RUNOFF FROM POULTRY LITTER-AMENDED FESCUEGRASS PLOTS

Runoff from land areas amended with poultry (Gallus gallus domesticus) manure can contain elevated concentrations of metals such as Cu, Fe, and Zn. Vegetative filter strips (VFS) can reduce runoff concentrations of animal manure components, but reported studies have typically focused on nutrients and solids rather than metals. This experiment assessed the impact of VFS length (0 to 12 m) on concentrations and mass losses of Cu, Fe, K, Na, Ni, and Zn in runoff from fescuegrass (Festuca arundinacea Schreb.) plots (1.5 m wide ×6 and 12 m long) treated with poultry litter. The runoff was produced from simulated rainfall applied at 50 mm h–1 until 1 h of runoff had occurred. Runoff Ni concentrations were below detection levels in all cases. Concentrations of Cu, Fe, K, Na, and Zn did not differ between litter-treated plot lengths but were significantly (p <0.001) affected by VFS length, decreasing in an approximately firstorder fashion. Means separation indicated that concentrations of Cu, Fe, K, and Zn did not significantly decrease after a VFS length of 3 m, while Na concentrations decreased up to a VFS length of 6 m. Mass transport of only Cu significantly decreased with increasing VFS, suggesting that VFS removal mechanisms such as adsorption to clay particles might play a larger role with regard to Cu than to Fe, K, Na, and Zn.