T. C. Daniel

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.

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.

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.

Soil Moisture Regimes of Three Conservation Tillage Systems

ABSTRACT COMPARISON of three conservation tillage systems, chisel plowing (CH), till-plant (TP) and no-till (NT), to conventional moldboard plowing (CN) indicates soil moisture advantages with conservation tillage vary. Volumetric water content (3-year average, 0-76 mm depth) at planting was 0.324, 0.279, 0.267 and 0.246 m^m-^ for NT, CH, TP, and CN, respectively. Average 3-year water content in the 0-0.25 m zone for weekly measurements during the growing season was 0.320, 0.309, 0.300, and 0.297 m^m^ for NT, CH, CN and TP, respectively. Soil moisture was higher in the NT treatment during most of the growing period. However, during a heavy rain period (93 mm), profile recharge in the CN, TP and NT treatments was 34, 34 and 44% less than for the CH treatment, respectively. Less water was removed from the 0.50-1.0 m zone of NT during extensive water depletion. For this soil with a 6-% slope, the NT treatment displayed the least water fluctuation during drying periods.

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.

Quality of Runoff from Four Northwest Arkansas Pasture Fields Treated with Organic and Inorganic Fertilizer

Long-term land application of animal manures, even at agronomic rates, can promote accumulation of soil phosphorus (P) which can, in turn, contribute to increased P loadings to downstream waters. The objective of this study was to assess the soil and runoff effects of replacing animal manure as a soil amendment with inorganic fertilizer (ammonium nitrate, NH4NO3) on fields that had been treated previously with animal manures. Runoff from two pairs of small fields (0.57 to 1.46 ha) was sampled from September 1991 to April 1994. All fields had been treated previously with animal manures; after runoff monitoring began, one field of each pair received only NH4NO3, while the other of each pair continued to receive animal manure. Both soil and runoff P concentrations exhibited statistically significant decreasing trends over the monitoring period. The results demonstrate the potential for positively influencing runoff quality in a relatively short duration by replacing animal manures with ammonium nitrate for fields already having sufficient soil P.

Long‐term phosphorus solubility in soils receiving poultry litter treated with aluminum, calcium, and iron amendments

Abstract Phosphorus (P) runoff from poultry litter applied to fields can adversely impact water quality. The majority of P in runoff from poultry litter is soluble, so decreasing the solubility of P could lessen the impact of poultry litter on water quality. The objective of this study was to determine long‐term P solubility in soils receiving poultry litter treated with aluminum (Al), calcium (Ca), and iron (Fe) amendments at various soil pHs. Soil pH was adjusted to 4.0, 5.0, 6.0, 7.0, and 8.0 using elemental sulfur (S) or CaCO3 with some soil left at its native pH. The pH‐adjusted soil was then incubated with either no litter (control), litter alone (litter control), or litter amended with alum, A12(SO4)3.16H2O, (100 or 200 g/kg), Ca(OH)2 (25 or 50 g/kg), or FeSO4 .7H2O (100 or 200 g/kg). The soil was then allowed to equilibrate in the dark at room temperature for 0, 7, 49, 98, and 294 days. After equilibration, soils were extracted with deionized water and soluble reactive P levels were determined. Wa...

Tillage and residue management influence on corn growth

Abstract The large proportion (nearly 90%) of soil covered by crop residue with no-tillage (NT 0 ) systems often results in decreased soil warming, reduced germination, and reduced early plant growth in parts of the Midwest section of the USA. We hypothesize that removal of some of the residue from the seeding zone could potentially improve crop production with NT 0 . Thus, we evaluated the impact of residue removal from a 30-cm-wide zone directly over the row in a no-tillage system (NT 30 ) compared to NT 0 and conventional moldboard tillage (CN) on soil growing degree days (GDD), soil temperature, and corn ( Zea mays L.) growth and yield. This investigation was conducted in 1987 and 1988 on a Plano silt loam soil (fine-loamy, mixed, mesic, Typic Hapludalfs). Maximum growth rate (MGR) and relative growth rate (RGR) were calculated from weekly measured dry matter and leaf area. Soil temperature at 0–50 cm deep was measured hourly. Soil GDD was calculated from average soil temperature measured at the soil surface and 5 cm deep. Maximum growth rate and RGR were not significantly different between NT 30 and CN treatments in 1987. However, mean values of MGR and RGR were significantly greater for NT 30 than for NT 0 in 1987. This occurred because soil temperature values with NT 30 were similar to those for CN and significantly greater than NT 0 . Maximum growth rate and RGR values with NT 30 were significantly greater than for CN in 1988. This may have resulted from a lower dry matter and leaf area index (LAI) with CN in 1988. During 1987, NT 30 compared to NT 0 had significantly greater time to emergence, MGR, RGR, and soil temperature in the seed zone (0–5 cm) and in the plow zone (0–20 cm). In 1988, NT 30 had greater MGR, RGR, and LAI compared to CN because of the conserved soil water in the top 0- to 15-cm layer during an excessively dry soil season. Based on this research, NT 30 will provide soil thermal and water conditions that are conducive to good plant growth and production while reducing the potential for soil erosion.