EFFECTIVENESS OF VEGETATIVE FILTER STRIPS IN CONTROLLING

LOSSES OF SURFACE-APPLIED POULTRY LITTER CONSTITUENTS

I. Chaubey, D. R. Edwards, T. C. Daniel, P. A. Moore Jr., D. J. Nichols

ABSTRACT. 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 (Testuca arundinacea Schreb.j plots (1.5 x 24.4 m) amended with poultry litter (5 Mg/ha). The VFS reduced mass transport of ammonia-nitrogen (NHyN), total Kjeldahl nitrogen (TKN), ortho-phosphorus (PO4-P), total phosphorus (TP), chemical oxygen demand (COD), and total suspended solids (TSS). Mass transport of TKN, NHyN, 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 (r^ = 0.70 to 0.94) by a first-order relationship between constituent removal and VFS length. Keywords, Runoff, Water quality. Animal manure. Poultry litter

Land application of animal manure is generally regarded as an economic means of making beneficial use of manure constituents. Runoff from land application sites, however, is a

potentially significant source of pollution, since it can contain undesirable concentrations of sediment, organic matter, nutrients, and microorganisms. The increasing size and concentration of animal production facilities in some regions have made land application of manure a topic of high public interest.

Use of vegetative filter strips (VFS) has received considerable attention for removing impurities in runoff from cropland and areas of livestock activity. Vegetative

Article was submitted for publication in August 1994; reviewed and approved for publication by the Soil and Water Div. of ASAE in May 1995. Presented as ASAE Paper No. 93-2011.

The investigation was supported in part by the United States Environmental Protection Agency under Assistance Agreement C9006706-91-1 to the Arkansas Soil and Water Conservation Commission. Further support was provided by the Arkansas Soil and Water Conservation Commission and the U.S. Department of the Interior, Geological Survey, through the Arkansas Water Resources Center. Mention of trade names of commercial products does not constitute endorsement or recommendation for use. This article is presented as a contribution to Regional Research Project S-249.

The authors are Indrajeet Chaubey, ASAE Student Member, Graduate Student, Biosystems and Agricultural Engineering Dept., Oklahoma State University, Stillwater, Oklahoma (former Graduate Student, Biosystems and Agrciultural Engineering Dept., Universityof Arkansas, Fayetteville); Dwayne R. Edwards, ASAE Member Engineer, Associate Professor, Biosystems and Agricultural Engineering Dept., University of Kentucky, Lexington; Tommy C. Daniel, Professor, Dept. of Agronomy, University of Arkansas, Fayetteville; Philip A. Moore Jr., Soil Chemist and Adjunct Associate Professor, USDA-Agricultural Research Service, Dept. of Agronomy, University of Arkansas, Fayetteville; and D. Jeff Nichols, Research Assistant, Dept. of Agronomy, University of Arkansas, Fayetteville. Corresponding author: Dwayne R. Edwards, Biosystems and Agricultural Engineering Dept., University of Kentucky, Lexington, KY 40546-0276; e-mail: <dedwards@bae.uky.edu>.

filter strips (also referred to as grass filters, vegetative buffer strips, filter strips, or buffer strips) consist of grass or other cover and are emplaced down slope of pollutant sources to remove sediment, nutrients, and other materials from the incoming runoff. While VFS can occur naturally, the term generally (and in this article) denotes a man-made nonpoint source pollution management practice. Vegetative filter strips can purify entering runoff by promoting infiltration of soluble pollutants, deposition of sediment and sediment-bound pollutants, and adsorption of pollutants onto soil and plant surfaces (Dillaha et al., 1989). Several studies have been conducted to investigate the use of VFS for nonpoint source pollution control, but there are currently no generally accepted methods for VFS design with respect to pollutant removal that fully account for the many different mechanisms that govern VFS performance. Consequently, VFS can be installed in areas and under conditions in which they are either ineffective or perhaps overdesigned.

Field studies involving runoff from cattle feedlots/bamyards (e.g., Westerman and Overcash, 1980; Young et al., 1980; Dickey and Vanderholm, 1981; Edwards et al., 1983; Dillaha et al., 1988; Schellinger and Clausen, 1992), cropland runoff (e.g., Dillaha et al., 1989; Magette et al., 1989; Michelson and Baker, 1993), and runoff from vegetated areas receiving various treatments (e.g., Doyle et al., 1975, 1977; Thompson et al., 1978; Paterson et al., 1980; Bingham et al., 1980; Overman and Schanze, 1985; Schwer and Clausen, 1989) indicate that VFS can be very effective in removing various constituents from incoming runoff. Depending on factors such as runoff rate, nature and length of the VFS, and pollutant source area characteristics, VFS can remove in excess of 90% of runoff constituents such as total Kjeldahl nitrogen (TKN), total phosphorus (TP), fecal coliforms, and total suspended solids (TSS). The nature of incoming flow is also reported to have a significant effect on VFS effectiveness; Dillaha

VOL. 38(6): 1687-1692

Transactions of the ASAE

1995 American Society of Agricultural Engineers 1687

etal. (1986) reported that VFS effectiveness decreased markedly following the development of concentrated flow within the VFS.

Several scientists have successfully described the capability of VFS to remove materials in incoming runoff through use of mathematical simulation models (Barfield etal., 1979; Kao and Barfield, 1978; Tollner et al., 1976, 1977; Hayes et al., 1979; Hayes and Hairston, 1983). One of the more recent modeling developments was reported by Lee et al. (1989), who developed an event-based model to simulate phosphorus transport in VFS.

The objective of this study was to test the effectiveness of VFS for the removal of sediment, nutrients, and organic matter from land areas amended with poultry litter. This work complements previous studies by examining poultry litter as the animal manure source as opposed to livestock manures, which have often been used in studies of this nature. The study also adds to prior work in that most studies have addressed use of VFS just beneath row-cropped land or feed lots; this work addresses VFS effectiveness just beneath pasture/range land.

MATERIALS AND METHODS Three plots with dimensions of 1.5 x 24.4 m (long axes

oriented down slope) were constructed on a Captina silt loam (fine-silty, mixed mesic, Typic Fragiudult) at the main Agricultural Experiment Station in Fayetteville, Arkansas (approximately 36°N Lat). Each plot was graded to a uniform 3% slope and bordered with rust-proofed metal to isolate runoff. A cover of fescue was established in spring 1992 by seeding at approximately 500 kg/ha. Wooden gutters were installed across each plot, with tops at ground surface level, at 3.1, 6.1, 9.2, 12.2, 18.3, and 24.4 m down slope of the top to enable collection of runoff at those locations (fig. 1). Each gutter had inside dimensions of 1.5 X 0.1 m and was fitted with a removable, water-tight cover that prevented water entry into the gutter during the nonsampling times.

Poultry litter was manually applied in May 1993 (approximately 13 months after seeding the plots) at 5 Mg/ha to the upper 3.1 m of each plot. The grass height was approximately 10 cm at the time of litter application, and the proportion of soil surface covered by the grass was essentially 100%. Prior to litter appHcation, soil samples (Oto 2.5 cm depth) were collected from each plot and analyzed by the University of Arkansas Agricultural Services Laboratory. The results of the soil analyses are

Table 1. Soil and poultry litter composition

Manured -

VFS \<jutters

Constituent

H2O Organic matter

pH

EC

Total N NH3-N NO3-N P K Fe Cu

22.5 0.7

5.3

Soil (%)

Concentration

(1.2t) (0)

(pH units)

(0.2)

(dS/m)

0.0177

557.7 1.6 1.5

75.7 36.5

129.2 6.5

(0.0005)

(mg/kg)

(25.8) (1.5) (1.5) (4.9)

(19.9) (7.6) (1.3)

Poultry litter*

24.61

8.5

6.0

33 100 4516

176 15 833 61900

101 467

(%)

(1.0)

(0)

(0)

(6686) (390)

(25) (462)

(4697) (30) (12)

* Mean of three replications; "as is" basis. t Standard deviation.

given in table 1. The composition of the poultry litter and application rates of selected litter constituents appear in tables 1 and 2, respectively. The litter application to the upper 3.1 m of the plots and the placement of the runoff collection gutters enabled assessment of effectiveness of VFS lengths of 0, 3.1, 6.1, 9.2, 15.2, and 21.4 m.

Four rainfall simulators (Edwards et al., 1992), altogether capable of applying rainfall to one complete plot, were used to supply rainfall at an intensity of 50 mm/h two days following litter application. The plots received no natural rainfall between litter application and the simulated rainfall. The municipal water that was used as the simulated rainfall source was sampled and analyzed for various constituents (table 3). The duration of simulated rainfall was 1 h after the beginning of runoff. Runoff samples were manually collected from the gutters approximately every 0.17 h. All runoff samples for a given sampling time were collected sequentially beginning with the gutter most distant from the source area. The times required to collect the samples were measured to enable computation of runoff rates and volumes.

Aliquots of the samples were filtered (0.45 jLim pore diameter) for ortho-phosphorus (PO4-P) and nitrate-nitrogen (NO3-N) analysis. The runoff samples were then refrigerated (4° C) and analyzed using standard methods (Greenberg et al., 1992) by the Arkansas Water Resources Center Water Quality Laboratory for TKN, ammonia-nitrogen (NH3-N), NO3-N, TP, PO4-P, chemical oxygen demand (COD), and TSS. The macro-Kjeldahl method was used for TKN analysis. Ammonia was determined by the ammonia-selective electrode method. Ion chromatography

Table 2. Nutrient application rates

Figure 1-Schematic of experimental field plot (not to scale).

Constituent

Total N NH3-N NO3-N P

Application Rate (kg/ha)

185.9 25.4

1.0 88.9

1688 TRANSACTIONS OF THE AS A E

Table 3. Municipal water composition

Constituent

TKN NH3-N NO3-N TP PO4-P

Concentration* (mg/L)

0.476 0.003 0.550 0.050 0.003

(0.011) (0.31) (0.00) (0.01) (0.03)

* Mean of three replications. t Standard deviation.

was used in analyses of NO3-N and PO4-P. Total P was analyzed by the ascorbic acid colorimetric method following sulfuric acid-nitric acid digestion. The closed reflux, colorimetric method was used for COD determinations.

The runoff amount and poultry litter constituent concentration data were used to compute mass losses of TKN, NH3-N, NO3-N, TP, PO4-P, COD, and TSS occurring at various VFS lengths. Analyses of variance were performed to determine the effects of VFS length on average concentration, average mass loss, and average proportion of mass loss reduction for the litter constituents studied. Least significant difference (LSD) testing was performed to determine significant differences in VFS length performance when analyses of variance indicated a significant overall VFS length treatment effect. All tests of significance were conducted at the p = 0.05 level.

RESULTS AND DISCUSSION VFS LENGTH EFFECTS ON LITTER CONSTITUENT CONCENTRATIONS

Table 4 contains flow-weighted mean runoff concentrations, averaged across replications, for all the investigated poultry litter constituents. Runoff concentrations of all constituents were significantly affected by VFS length, although concentrations of TSS and COD did not decrease significantly after a VFS length of 3.1 m. The data generally indicate the influences of filtration by the grass, dilution by the simulated rainfall, and infiltration of soluble poultry litter constituents. Decreasing concentrations of litter constituents, however, were expected since dilution will occur if the simulated rainfall is relatively pure in comparison to the runoff and if

the VFS topsoil is relatively pure in comparison to the manure-treated topsoil.

VFS LENGTH EFFECTS ON LITTER CONSTITUENT MASS TRANSPORT

Data on mean mass transport measured at each VFS length are given in table 5. Except for the case of NO3-N, VFS length treatment had an overall significant effect on the mass transport of all poultry litter constituents investigated. Means separation according to VFS length treatment level, however, indicated variation in the VFS lengths beyond which no further mass transport reduction occurred. Mass transport of TKN, NH3-N, and PO4-P significantly decreased up to a VFS length of approximately 9.2 m. Mass transport of TP decreased up to a VFS length of 6.1 m, while mass transport of COD and TSS decreased only up to a VFS length of 3.1 m. Mass transport of NO3-N tended to increase (although not significantly) with VFS length and averaged 0.82 kg/ha. It is likely that the predominant source of NO3-N in the runoff was the simulated rainfall itself (table 3), the soil, and/or the grass, since (a) the NO3-N content of the poultry litter was low, and (b) the short time and dry conditions between litter application and rainfall would not have promoted NO3-N formation. A reduction in runoff NO3-N transport might have been observed if the simulated rainfall NO3-N concentration had been low relative to that of the litter. Mass transport data for the other constituents, however, indicate that mass is being removed as the runoff travels down slope. Except for the case of NO3-N, then, the data of table 5 indicate that decreasing concentrations of constituents shown in table 4 are due to filtration mechanisms (i.e., infiltration and trapping/adsorption to grass and/or debris) as well as to dilution.

Infiltration appears to be the mechanism most responsible for mass removal of P. Although some P was associated with the solids in runoff, most (64%, table 4) was in the soluble PO4-P form, in which case a deposition mechanism would not have been applicable. Infiltration might also be responsible for the majority of N removed by the VFS from the incoming runoff, since there is evidence that the organic N in poultry litter (which, in this case, accounted for 85% of the total N) is comprised primarily of soluble uric acid (e.g., Schefferle, 1965) and would presumably not be subject to physical filtration or deposition. Experiments that include partitioning incoming

Table 4. Mean* poultry litter constituent concentration as a function of VFS length

Table 5. Mean* poultry litter constituent mass transport as a function of VFS length

Constituent

0

TKN 26.50at NH3-N 7.15a NO3-N 0.67a TP 6.72a PO4-P 4.29a TSS 61.60a COD 170.68a

3.1

6.88b 2.02b 0.62b 2.22b 1.38b

22.26b 53.11b

VFS Length (m)

6.1 9.2

(mg/L)

4.68bc 0.90bc 0.56c 1.04bc 0.75bc

16.78b 37.25b

3.03bc 0.64bc 0.55c 0.59bc 0.44bc

19.10b 32.94b

15.2

1.85c 0.12c 0.52cd 0.28c 0.20c

11.05b 19.49b

21.4

1.67c 0.05c 0.50d 0.22c 0.17c

12.52b 19.54b

Constituent

0

NO3-N 0.4at TKN 15.5a NH3-N 4.2a TP 4.0a PO4-P 2.5a TSS 35.9a COD 101.4a

3.1

0.7a 9.2b 2.2b 2.3b 1.5b

22.7ab 56.3b

VFS Length

6.1

(m)

9.2

(kg/ha source area)

0.9a 7.1bc 1.3bc 1.5bc l.lbc

23.8ab 54.9b

1.0a 5.1bc l.Ocd 0.9c 0.7cd

29.8ab 50.1b

15.2

1.1a 4.2c 0.3cd 0.6c 0.4d

20.2b 37.2b

21.4

0.9a 3.4c O.ld 0.4c 0.3d

18.6b 31.1b

* Mean of three replications. t Within-row means followed by the same letter are not significandy

different by LSD test.

* Mean of three replications. t Within-row means followed by the same letter are not significantly

different by LSD test.

VOL. 38(6): 1687-1692 1689

poultry litter constituents into solid and soluble phases will be necessary to better assess the relative importance of infiltration and other mechanisms in terms of VFS effectiveness.

A first-order equation was used to describe the relationship between mass transport of litter constituents and VFS length. The equation used was:

M: LL = '- ^ 1 , 0 ^^^^ (1)

where M; ,L = mass transport (kg/ha) of constituent I

transported past VFS length L (m) Mj o = mass transport (kg/ha) of constituent I initially

entering the VFS kj = rate coefficient (1 /m) for constituent I

The parameters kj were determined from linear regressions of natural logarithms of mass transport data against VFS length. The values of kj are given in table 6. No data for TSS and NO3-N are shown, because the coefficient of determination for TSS was insignificant, and NO3-N transport was unaffected by VFS length.

Figure 2 demonstrates the relationship between mean observed and regression (first-order) mass transport of NH3-N, TP, and PO4-P. In all cases, regression mass transport values were comparable to the observed values (table 5 and fig. 2).

VFS LENGTH EFFECTS ON PROPORTIONS OF MASS TRANSPORT REDUCTION

VFS length effectiveness was computed for each poultry litter constituent from:

Ey = 100[(M^j-Mij)/Moj] (2)

where

MiJ

M. 00

= effectiveness (%) of VFS length I for constituent J

= mass of constituent j transported past VFS length I

= mass of constituent j transported past the zero VFS length (i.e., initially entering the VFS)

The effectiveness values of the various VFS lengths with respect to the poultry litter constituents are indicated in table 7. No values are shown for NO3-N since, as discussed earlier, mass transport of this constituent was independent of VFS length. Furthermore, no data for TSS or COD are given in table 7, because the VFS effectiveness with regard to these constituents did not vary with VFS length for lengths of from 3.1 to 21.4 m. The average effectiveness (computed for all lengths and replications) of the VFS for

Table 6. Results of linear regression analysis for determination of rate coefficients of the first-order kinetic equation (Mj L = Mi,oe t j L )

Constituent (m-i)

TKN NH3-N TP PO4-P COD

-0 .084 -0 .174 -0.123 -0.113 -0 .064

0.791 0.995 0.932 0.942 0.698

o Q .

— I — I — I — I — I — I — I — I — I — I — I — I — I — I — r -

NH3-N (Predicted) • NH3-N (Observed)

TP (Predicted) • TP (Observed)

PO4-P (Predicted) PO4-P (Observed)

5 10 15

VFS length, m

20 25

Figure 2-Predicted (first-order) and observed mass transport of NH3-N, TP, and PO4-P as functions of VFS length.

TSS was 34.5%, whereas the VFS were 50.7% effective in reducing incoming COD transport.

Results in table 7 indicate that a 21.4-m VFS length was from 80.5 to 98.0% effective in reducing incoming mass transport of TKN, NH3-N, TP, and PO4-P. The LSD testing of the mean effectiveness values, however, indicates that the effectiveness in terms of TKN and TP removal was constant for VFS lengths of 9.2 m and greater. Effectiveness of NH3-N and PO4-P removal increased up to a VFS length of 15.2 m.

CONTEXT AND APPLICABILITY OF RESULTS This study focused on only the first runoff event

following poultry litter application to the VFS source area; thus, it was not a "long-term" study. In the context of this particular VFS application, however, the results are nonetheless useful. The emphasis on the first post-litter-application runoff event is justifiable because it has been demonstrated to be far worse in terms of quality of treated area runoff than succeeding runoff events (McLeod and Hegg, 1984; Edwards and Daniel, 1994). Edwards and Daniel (1994), for example, found that 80% of all solids

Constituent

TKN NH3-N TP PO4-P

Table 7. Mean* VFS length effectiveness

3.1 (%)

39.2ct 46.6c 39.6c 38.8d

6.1 (%)

53.5bc 69.8b 58.4bc 55.1cd

VFS Length (m)

9.2 (%)

66.6ab 77.6b 74.0ab 70.5bc

15.2 (%)

75.7a 94.1a 86.8a 84.9ab

21.4 (%)

80.5a 98.0a 91.2a 89.5a

* k is rate coefficient, and r̂ is coefficient of determination.

* Mean of three replications. t Within-row means followed by the same letter are not significantly

different by LSD test.

1690 TRANSACTIONS OF THE A S A E

losses occurring during four rainfall events occurred during the first runoff event following poultry litter application to fescue. Minimizing first post-application runoff losses of poultry litter constituents is therefore critical to minimizing total constituent losses.

The long-term effectiveness of VFS would be an issue of concern in a use of VFS below pasture if there were evidence of accumulation of nutrients, sediment, or other litter constituents. Investigations of runoff losses of poultry constituents applied to fescue, however, have consistently demonstrated that nutrient losses are typically quite low (only a few percent of amounts applied) (Edwards and Daniel, 1993; 1994). It is therefore more likely that incoming nutrients in runoff from amended pasture will be insufficient to maintain optimal grass density within the VFS than that nutrients will accumulate within the VFS. Available information also suggests that when VFS are used below pasture, effectiveness will not be appreciably degraded due to a build-up of solids within the VFS. Reported solids losses from fescue pasture treated with poultry litter are relatively low in comparison to those that are characteristic of cropland or feedlots (Edwards and Daniel, 1993; 1994). In addition, most (by far) of the solids transported from litter-treated fescue consist of litter particles (as opposed to soil) that can decompose rather rapidly (Edwards et al., 1994). In view of the preceding discussion, it appears likely that VFS used to remove pollutants transported from pasture will not experience some of the same processes that significantly diminish long-term effectiveness of VFS installed down slope of cropland, feedlots, or other sources that provide a relatively high and constant pollutant input.

It was recognized that the litter-treated "source area" was small in comparison to the VFS. A longer litter-treated source area, as would be more typical in actual practice, would have increased hydraulic and pollutant loadings to the VFS and thus altered some VFS performance measures. The focus of this study, however, was on characterizing VFS effectiveness as a function of VFS length rather than hydraulic and pollutant loadings. More comprehensive studies that eventually address all major factors that influence VFS performance are needed, because the effects of those factors and their interactions will ultimately be necessary to best implement VFS technology in situations outside the reported collective database.

SUMMARY AND CONCLUSIONS Poultry litter was applied at 5 Mg/ha to the upper 3.1m

of 24.4 m long grassed (fescue) plots. The remainder of the plots acted as a VFS for the runoff produced by simulated rainfall (50 mm/h). Runoff was sampled at selected down slope distances, analyzed, and used to compute concentrations of poultry litter constituents, mass transport of the constituents past the sampling points, and effectiveness of the various VFS lengths in reducing constituent mass transport.

The VFS removed significant quantities of TKN, NH3-N, TP, PO4-P, TSS, and COD from incoming runoff. Removal of NH3-N and PO4-P increased up to a VFS length of 15.2 m. Increases in TKN and TP removal were observed up to a VFS length of 9.2 m, while TSS and COD

removal did not increase beyond a VFS length of 3.1 m. The VFS appeared to be ineffective in removing NO3-N from incoming runoff, but their effectiveness could have been masked by the relatively high NO3-N concentration of the simulated rainfall.

Fescue VFS appear to hold promise for improving quality of runoff from source areas treated with poultry litter, if considerations mentioned in the introductory portion of this article are followed. Additional work is needed to determine the effect of source area to filter area ratio on VFS effectiveness and to quantify impacts of other variables such as type of vegetation and incoming flow rate on VFS performance.

REFERENCES Barfield, B. J., E. W. Tollner and J. C. Hayes. 1979. Filtration of

sediment by simulated vegetation, 1. Steady-state flow with homogeneous sediment. Transactions oftheASAE 22(3):540-545, 548.

Bingham, S. C , R W. Westerman and M. R. Overcash. 1980. Effect of grass buffer zone length in reducing the pollution from land application areas. Transactions oftheASAE 23(2):330-335, 342.

Dickey, E. C. and D. H. Vanderholm. 1981. Vegetative filter treatment of livestock feedlot runoff. / . Environ. Qual. 10(3):279-284.

Dillaha, T. A., R. B. Reneau, S. Mostaghimi and D. Lee. 1989. Vegetative filter strips for agricultural nonpoint source pollution control. Transactions oftheASAE 32(2):513-519.

Dillaha, T. A., J. H. Sherrard and D. Lee. 1986. Long-term effectiveness and maintenance of vegetative filter strips. VPI-VWRRC-BULL 153:1-39.

Dillaha, T. A., J. H. Sherrard, D. Lee, S. Mostaghimi and V. O. Shanholtz. 1988. Evaluation of vegetative filter strips as a best management practice for feed lots. J. Water Pollution Control F^^. 60(7): 1231-1238.

Doyle, R. C , G. C. Stanton and D. C. Wolf. 1977. Effectiveness of forest and grass filters in improving the water quality of manure polluted runoff. ASAE Paper No. 77-2501. St. Joseph, Mich.: ASAE.

Doyle, R. C , D. C. Wolf and D. R Bezdicek. 1975. Effectiveness of forest buffer strips in improving the water quality of manure polluted runoff. In Managing Livestock Wastes, Proc. 3rd Int. Symp. on Livestock Wastes, 299-302. St. Joseph, Mich.: ASAE.

Edwards, D. R. and T. C. Daniel. 1993. Effects of poultry litter application rate and rainfall intensity on quality of runoff from fescuegrass plots. 7. Environ. Qual. 22(2):361-365.

. 1994. Quality of runoff from fescuegrass plots treated with poultry litter and inorganic fertilizer. J. Environ. Qual. 23(3):579-584.

Edwards, D. R., T. C. Daniel, R A. Moore Jr. and A. N. Sharpley. 1994. Solids transport and erodibility of poultry litter surface-applied to fescue. Transactions oftheASAE 37(3):771-776.

Edwards, D. R., L. D. Norton, T. C. Daniel, J. T. Walker, D. L. Ferguson and G. A. Dwyer. 1992. Performance of a rainfall simulator. Arkansas Farm Research 41(2): 13-14.

Edwards, W. B., L. B. Owens and R. K. White. 1983. Managing runoff from a small, paved beef feedlot. J. Environ. Qual. 12(2):281-286.

Greenberg, A. E., L. S. Clesceri and A. D. Eaton. 1992. Standard Methods for the Examination of Water and Wastewater, 18th Ed. Washington, D.C.: Am. Public Health Assoc.

Hayes, J. C , B. J. Barfield and R. I. Bamhisel. 1979. Filtration of sediment by simulated vegetation II. Unsteady flow with non-homogeneous sediment. Transactions oftheASAE 22(5): 1063-1067.

VOL. 38(6): 1687-1692 1691

Hayes, J. C. and J. E. Hairston. 1983. Modeling the long-term effectiveness of vegetative filters on on-site sediment controls. ASAE Paper No. 83-2081. St. Joseph, Mich.: ASAE.

Kao, T. Y. and B. J. Barfield. 1978. Predictions of flow hydraulics of vegetated channels. Transactions of the ASAE 21(3): 489-494.

Lee, D., T. A. Dillaha and J. H. Sherrard. 1989. ModeHng phosphorous transport in grass buffer strips. ASCE J. Environ. Engr.Div. 115(2): 409-427.

Magette, W. L., R. B. Brinsfield, R. E. Palmer and J. D. Wood. 1989. Nutrient and sediment removal by vegetated filter strips. Transactions of the ASAE 32(2):663-667.

McLeod, R. V. and R. O. Hegg. 1984. Pasture runoff water quality from application of inorganic and organic nitrogen sources. J. Environ. Qual. 13(1): 122-126.

Michelson, S. K. and J. L. Baker. 1993. Buffer strips for controlling herbicide runoff losses. ASAE Paper No. 93-2084. St. Joseph, Mich.: ASAE.

Overman, A. R. and T. Schanze. 1985. Runoff water quality from waste water irrigation. Transactions of the ASAE 28(5): 1535-1538.

Paterson, J. J., J. H. Jones, F. J. Olsen and G. C. McCoy. 1980. Dairy liquid waste distribution in an overland flow vegetative-soil filter system. Transactions of the ASAE 23(4):973-977, 984.

Schefferle, H. E. 1965. The decomposition of uric acid in built up poultry litter. J. Applied Bacteriol. 28(3):412-420.

Schellinger, G. R. and J. C. Clausen. 1992. Vegetative filter treatment of dairy barnyard runoff in cold regions. J. Environ. Qual. 21(l):40-45.

Schwer, C. B. and J. C. Clausen. 1989. Vegetative filter treatment of dairy milkhouse waste water. J. Environ. Qual. 18(4):446-451.

Thompson, D. B., T. L. Loudon and J. B. Gerrish. 1978. Winter and spring runoff from manure application plots. ASAE Paper No. 78-2032. St. Joseph, Mich.: ASAE.

Tollner, E. W, B. J. Barfield, C. T. Haan and T. Y. Kao. 1976. Suspended sediment filtration capacity of simulated vegetation. Transactions of the ASAE 19(4):678-682.

Tollner, E. W, B. J. Barfield, C. Vachirakomwatana and C. T. Haan. 1977. Sediment deposition patterns in simulated grass filters. Transactions of the ASAE 20(5): 940-944.

Westerman, P. W. and M. R. Overcash. 1980. Dairy open lot and lagoon-irrigated pasture runoff quantity and quality. Transactions of the ASAE 23(5): 1157-1164, 1170.

Young, R. A., T. Huntrods and W. Anderson. 1980. Effectiveness of vegetated buffer strips in controlling pollution from feedlot runoff. J. Environ. Qual. 9(3):483-487.

1692 TRANSACTIONS OF THE ASAE