| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
a School of Environment and Natural Resources, The Ohio State University, 2021 Coffey Rd., Columbus, OH 43210-1085
b Environmental Soil Science, Univ. of Missouri-Columbia, 302 Anheuser-Busch Natural Resources Building, Columbia, MO 65211
* Corresponding author (blanco.16{at}osu.edu)
Received for publication February 19, 2006.
 |
ABSTRACT |
|---|
 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
Abbreviations: B-FS, grass barriers above filter strips • CF-B-FS, grass barriers above filter strips in concentrated flow • CF-FS, filter strips in concentrated flow • FS, filter strips • NPS, nonpoint source
|
INTRODUCTION |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
While barriers and FS are effective for controlling transport of sediment and sediment-bound nutrients (Daniels and Gilliam, 1996; Eghball et al., 2000; Blanco-Canqui et al., 2004b), their performance depends on the runoff flow conditions (Dosskey et al., 2002). Studies suggest that FS are less effective in controlling NPS pollutant transport in concentrated runoff leaving large agricultural areas because they are prone to overtopping and inundation (Blanco-Canqui et al., 2004a). While there are questions on the effectiveness of FS in concentrated flow, actual quantitative field and plot data comparing FS performance under interrill and concentrated flow are limited. A review of FS research has highlighted the need for conducting field studies designed to assess the FS performance for reducing transport sediment and nutrients under concentrated runoff (Krutz et al., 2005).
Grass barriers may offer higher hydraulic resistance to concentrated runoff because of their stiff stems and upright growth (Dunn and Dabney, 1996; Blanco-Canqui et al., 2004b), but field and plot studies designed to document the performance of barriers under interrill and concentrated flow conditions are also few. A lab study by Meyer et al. (1995) showed that switchgrass barriers, planted across concentrated flow channels, ponded runoff up to 400 mm above the barriers, trapping 
90% of coarse sediments. A related lab study by Dabney et al. (1995) reported that barriers ponded concentrated runoff and deposited sediment above the barriers more than FS did. Gilley et al. (2000) showed that switchgrass barriers changed the surface hydrology of the soil by ponding runoff above barriers, thereby reducing interrill flow in croplands. Some studies have suggested that barriers may be more effective at trapping sediments than at reducing runoff (Self-Davis et al., 2003). In a field study, Dabney et al. (2004) observed that switchgrass barriers planted at 0.5-m intervals across concentrated flow channels showed potential for stabilizing gullies and reducing soil erosion in sloping lands. The potential of barriers for reducing runoff, sediment, and nutrient transport is partly attributed to the improved soil structure. Soils under long-term switchgrass barriers often have lower bulk density and higher macroporosity (Rachman et al., 2004a), and higher saturated hydraulic conductivity and water infiltration rates (Rachman et al., 2004b) which can reduce runoff (Gilley et al., 2000).
Blanco-Canqui et al. (2004a, 2004b) compared the effectiveness between barriers and FS for reducing sediment and nutrient transport in interrill and concentrated runoff. However, the authors did not assess the effectiveness of each conservation practice separately under interrill and concentrated flow. Field data on individual performance of barriers or FS are needed for proper design, use, and management. Data are also needed for the development and validation of models to predict performance of barriers and FS for reducing transport of NPS pollutants (Srivastava et al., 1998; Krutz et al., 2005). The hypotheses of this study were that: (1) the FS are effective under interrill runoff, but their effectiveness in concentrated flow is significantly less, and (2) barriers remain equally effective under both interrill and concentrated flow. If these hypotheses hold, it would suggest that barriers may be used as a companion treatment to FS to enhance the effectiveness of FS to reduce concentrated runoff from agricultural fields, and reduce the amount of land usually required for FS establishment when they are used by themselves. Although barriers alone may remove significant amounts of sediment in runoff, wider buffers may be needed for effective removal and transformation of dissolved NPS pollutants (Dabney et al., 2006). We hypothesize that wider buffers consisting of FS accompanied by barriers above may be an alternative for reducing NPS pollution in concentrated runoff. The study objectives were to assess the effectiveness of (1) FS alone, and (2) switchgrass barriers planted above FS for reducing runoff, sediment, N, and P loss in interrill and concentrated flow conditions.
|
MATERIALS AND METHODS |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
This paper only evaluates four treatments including FS, CF-FS, CF-B-FS and B-FS because the objective of the study was to compare the performance between B-FS and CF-B-FS and between FS and CF-FS for reducing sediment and nutrient transport in interrill and concentrated flow. Data from all six treatments were, however, used in statistical analysis per the original design to improve the statistical power. This study was designed to compare the effectiveness of each conservation practice separately under interrill and concentrated flow. Information from this study would be useful to the design and management of these grass systems under the two types of runoff. Comparison of performance between B-FS and FS and between CF-B-FS and CF-FS were reported in a companion study (Blanco-Canqui et al., 2004b).
The plots were oriented up- and downslope along the dominant soil slope, and bordered with 200-mm-high by 250-mm-wide soil berms treated with polyacrylamide at a rate of 9 kg ha–1 and Du Pont nonwoven geotextile fabric (Blanco-Canqui et al., 2004c). Plots had an upslope 1.5- by 8-m pollutant source area managed under continuous cultivated fallow, above a downslope FS of equal size. The source area was tilled with a rototiller to a depth of 80 mm in July 2001 and also rototilled after rainfall events. A 0.7-m barrier was established from mature transplants at the downslope edge of the source area just above a FS in July 2001. Existing fescue was used as FS in both treatments and periodically mowed to 100 mm high. A 200-mm-wide by 100-mm-deep v-shaped channel was constructed in the center of the pollutant source area of CF-FS and CF-B-FS to simulate concentrated flow.
Rainfall Simulation and Runoff Collection
A rotating-boom rainfall simulator was used to apply rainfall to assess the performance of the treatments (Swanson, 1965). The simulator was positioned between two plots and supplied rainfall to a plot pair at 66 ± 5 mm h–1. A dry-run rainfall application of 1 h was applied 24 h before wet-run application of the same intensity and duration. The dry and wet rainfall applications were selected to match natural rainfall events with a 10-yr return period for mid-Missouri (Hershfield, 1961). Fertilizer was applied at 80 kg ha–1 of N, 35 kg ha–1 of P, and 66 kg ha–1 of K to the source area 24 h before rainfall. No crop was grown, and fertilizer was applied only to assess the treatment effectiveness for trapping nutrients.
V-shaped collectors (0.08 m wide, 1.5 m long, and 0.06 m deep) were constructed of angle iron to sample runoff water. They had a hinged cover fitted with a watertight gasket to close it to the V-shaped trough. Collectors could be opened and closed quickly between sampling periods because of the hinged covers. Collectors were installed perpendicular to the soil slope and across the plot width at 1 m above the downslope edge of the source area and in the FS area at 0.7, 4, and 8 m below the source area. A V-shaped groove was cut in the soil to place the collector. Collectors were tightly anchored with four steel spikes (10 mm diam. by 250 mm long) to eliminate runoff undercutting below. Collection pits of 300-mm diam. by 250-mm depth were sited just outside the plot area to place sampling containers. Collectors were set to a 3% slope of hydraulic head to facilitate water flow into containers in collection pits.
Runoff was sampled every 10 min. for 5 s at all sampling positions during the 1-h wet-runs. Samples were collected first from the collector at the lower end of the plot and then successively from each collector upslope (Chaubey et al., 1994) to prevent runoff flow from breaking downstream (Srivastava et al., 1996). Total runoff volume was regressed against time of collection, and the resulting regression equations were integrated over time from 0 to 60 min to compute runoff volume on a 1-h basis. Runoff depth was computed as the ratio of the runoff volume to the contributing area above a sampling point in accord with similar studies (Gilley et al., 2000).
Sediment, Nitrogen, and Phosphorus Analysis
Two aliquots of runoff were taken for the sediment, N, and P analyses. One 0.5-L aliquot was used for determination of sediment concentration. One composite 0.25-L aliquot for each sampling position over time was used for the N and P analysis. Runoff sediment concentration was measured by evaporation (Brakensiek et al., 1979). Samples for nutrient analysis were stored in an insulated cooler, transported to the laboratory, and immediately filtered through a Whatman #1 filter paper for determining nitrate (NO3–N), ammonium (NH4–N), and orthophosphate (PO4–P) concentrations. Total N and P concentrations were determined from the unfiltered sample volumes. Analysis of N and P was conducted using a Lachat flow injection analyzer (Lachat QuikChem 800, Zellweger Analytics, Milwaukee, WI). Sediment and nutrient masses were computed as the product of runoff and concentration (Eghball et al., 2000). Organic N was calculated as the difference between NO3–N and NH4–N from total N, whereas particulate P was the difference between total P and PO4–P (Eghball et al., 2000). Runoff sediment was divided by the corresponding contributing area above a sampling point to compute sediment mass per unit area.
Addition of Inflow
Additional runoff inflow was added at the top of the plots to expand the assessment of the effectiveness of the treatments for controlling concentrated flow. Additional inflow simulated greater runoff that would be expected to occur from a larger sediment source area. Inflow was applied at 2.5, 5.0, 7.5, 10.0, and 12.5 L min–1 to simulate sediment source areas of 1.2, 1.4, 1.6, 1.8, and 2 times (1.2x, 1.4x, 1.6x, 1.8x, and 2x) the actual plot size. Inflow was added simultaneously with 62.5 ± 5 mm h–1 of simulated rainfall by pumping from a 3.7-kL polyethylene tank coupled with flow rate regulators (Omega FP-5300, Eng., Stamford, CT). Inflow entered plots through a 1.5-m-wide, 80-mm-i.d. pipe placed on the contour across the plot width. The pipe had 10-mm-diam. holes at 50-mm intervals on the downslope side to deliver water onto a 0.15- by 1.5-m piece of geotextile fabric used to reduce scour erosion. Inflow was started 10 min after the initiation of simulated rain and continued throughout the duration of rainfall. Inflow was applied for a period of 15 min after which runoff samples were collected for that inflow. The inflow rate was then increased to the next higher rate, and the process of sampling was repeated. Runoff weight was measured by location, and aliquots were taken only for measurement of sediment concentrations. Runoff and sediment mass were integrated over time for a total of 15 min of simulation.
Statistics
The General Linear Models (GLM) procedure of SAS (SAS Institute, 2005) was used to conduct the analysis of variance (ANOVA) to test the hypotheses that differences in runoff, sediment, and nutrient reduction between adjacent sampling positions (–1 and 0.7, 0.7 and 4, and 4 and 8 m) were the same for interrill and concentrated flow conditions. Orthogonal contrasts were used to test the main effects for FS, CF-FS, CF-B-FS, and B-FS. The percent values of runoff, sediment, or nutrient were computed using Eq. [1]
 | [1] |
|
RESULTS AND DISCUSSION |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
|
|
|
The lower effectiveness of CF-FS was attributed to the bending of grass stems by concentrated runoff and channelization of flow near the edge of the sediment source area. The filtering capacity of the CF-FS treatment declined with increased transport capacity of the concentrated runoff. We observed that the upper 1-m CF-FS adjoining the field edge was partially inundated with runoff at the end of 1 h of rain simulation with supplemental runoff. We hypothesize that the lower effectiveness of the CF-FS is related to the reduction in hydraulic roughness and stiffness of the fescue stems. It is conceivable that concentrated runoff velocity in CF-FS was higher through the filter strips, reducing settling and infiltration of fine sediments when compared to interrill flow in FS.
Nitrogen and Phosphorus
Nutrient reductions between FS and CF-FS were variable. The FS removed organic N (Fig. 1B) and NO3–N (Fig. 1C) more than CF-FS at the 0.7-m position (P < 0.01), but differences in other nutrients were not significant. The FS removed 62% of organic N and 34% of NO3–N, whereas the CF-FS removed only 43% of organic N and 21% of NO3–N. On average, the 0.7-m FS and CF-FS removed 54% of particulate P, 30% of NH4–N, and 58% of PO4–P (Table 1). As with sediment, results showed that the effectiveness of narrow FS for removing organic N and NO3–N was significantly reduced with concentrated runoff. The low effectiveness of FS under concentrated flow for removing organic N mirrored the low sediment reduction for this treatment. Sediment removal was correlated to organic N (r2 = 0.98; P < 0.01). It was somewhat surprising that differences in P removal between FS and CF-FS were not significant. One might expect that the higher sediment reduction by FS may also result in higher reduction of particulate P as with organic N. High variability in data may have diminished differences in sediment P between the FS and CF-FS. Removal of particulate P rapidly increased, however, with an increase in treatment width.
Reduction in N loss increased with treatment width for both flow conditions, and nutrient removal between FS and CF-FS did not differ at the 4- and 8-m positions except for NO3–N (P < 0.05). The 4-m strip removed 70% of NO3–N under interrill and 49% under concentrated flow, whereas the 8-m strip removed 83% under interrill and 63% under concentrated flow. Greater filtering of sediments and improved infiltration may be the reasons for the higher reduction of NO3–N in FS (Daniels and Gilliam, 1996). Results suggest that concentrated runoff leaving fields with little or no vegetative and/or residue cover diminishes the effectiveness of narrow FS for controlling losses of organic N and NO3–N.
Performance of Grass Barriers with Filter Strips in Interrill and Concentrated Flow
Runoff and Sediment
Differences in runoff and sediment reduction between B-FS and CF-B-FS were not significant at any sampling position (P > 0.10; Table 2). Both B-FS and CF-B-FS reduced 17% of runoff at the 0.7-m and 34% at the 8-m sampling positions. They reduced an average of 92% of sediment transport at 0.7 m (Table 1). The addition of supplemental inflow did not significantly decrease the performance of barriers. Reduction of sediment transport increased with distance. About 97% was trapped at the 4-m and 99% at the 8-m position, showing that the greatest sediment reduction occurred in the 0.7 m. The B-FS and CF-B-FS spread runoff and created temporary ponding of runoff above the barriers, thereby inducing sediment deposition and thus minimizing sediment in downstream runoff. Runoff ponding depth was 20% more and occupied 25% more area extending above the barriers, forming a larger delta. Barriers did not fail for the conditions of this study.
Based on these results, barriers combined with FS offer a promise for reducing offsite movement of sediment in concentrated runoff. Results agreed with those of Rey (2004) who reported that vegetative barriers can be effective for reducing sediment losses from highly eroded environments with steep slopes. Runoff dispersion by barriers can reduce the runoff energy and velocity to transport sediment in accord with Dabney et al. (2004), who observed that barriers do not only reduce gully erosion but also stabilize field gullies. Our results show that barriers planted immediately above FS can improve the performance of FS and prevent them from being overtopped with sediment-loaded runoff.
Combinations of various plant species for sediment and nutrient control has been shown as a potential and innovative soil erosion control practice (Sheridan et al., 1999). Grass species within mixtures interact and often increase infiltration and macroporosity better than single species.
Nitrogen and Phosphorus
No significant differences in nutrient removal between the B-FS and CF-B-FS treatments were found for any width (Table 2). The 0.7 m of B-FS and CF-B-FS treatment was highly effective, removing >50% of runoff nutrients measured at the edge of the source area. On the average, 70% of organic N, 54% of NO3–N, 50% of NH4–N, 65% of particulate P, and 60% of PO4–P were removed by 0.7 m of buffer. At 8 m, B-FS removed 92% of organic N, 98% of particulate P, 89% of NO3–N, 91% of NH4–N, and 90% of PO4–P, whereas CF-B-FS removed 92% of organic N, 94% of particulate P, 73% of NO3–N, 91% of NH4–N, and 89% of PO4–P. These results indicated that within the scope of our study, barriers in conjunction with filter strips remained equally effective for reducing transport of nutrients under both interrill and concentrated flow conditions. The reduction of nutrient transport increased with distance.
|
CONCLUSIONS |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
Conversely, 0.7 m grass barriers with FS are effective for controlling soil (>90%) and nutrient (>50%) losses under both interrill and concentrated flow conditions. Increased effectiveness of barriers suggests that barriers can be used as a companion treatment to FS for reducing transport of NPS pollutants from agricultural fields. Increase in FS width from 0.7 m to 8 m increased significantly the performance of FS under concentrated flow. The sediment reduction under concentrated flow was only 3% lower than under interrill flow, implying that wide FS may be needed to significantly control the transport of NPS pollutants in concentrated flow although this measure would increase the land taken out of active production. The 0.7 m of barriers in conjunction with FS removed 92% of sediment whereas FS alone of the same width removed only 60% under concentrated flow, which suggested that a combination of 0.7-m barriers with FS may be a potential alternative to minimize the loss of production land for the establishment of wide FS for concentrated flow control.
It is important to mention that caution should be exercised when transferring the study results to field conditions. Performance of barriers under on-farm conditions may differ from that for plot settings. Larger rainfall storms (>65 mm h–1) and higher concentrations of incoming runoff mingled with steeper soil slopes than those tested in this study will eventually cause the failure of grass barriers. The performance of barriers with FS is expected to depend on storm intensity, field slope, and management of the source area. Determination of threshold levels of the performance of grass barriers combined with FS for reducing concentrated flow under on-farm conditions is a research priority for large-scale use of these erosion control practices.
|
ACKNOWLEDGMENTS |
|---|
|
NOTES |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
|
REFERENCES |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
This article has been cited by other articles:
|
|
 |
|
  C. C. Hoffmann, C. Kjaergaard, J. Uusi-Kamppa, H. C. B. Hansen, and B. Kronvang Phosphorus Retention in Riparian Buffers: Review of Their Efficiency J. Environ. Qual., August 24, 2009; 38(5): 1942 - 1955. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. Fiener and K. Auerswald Effects of Hydrodynamically Rough Grassed Waterways on Dissolved Reactive Phosphorus Loads Coming from Agricultural Watersheds J. Environ. Qual., February 6, 2009; 38(2): 548 - 559. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. M. Dabney, K.C. McGregor, G.V. Wilson, and R.F. Cullum How Management of Grass Hedges Affects their Erosion Reduction Potential Soil Sci. Soc. Am. J., January 1, 2009; 73(1): 241 - 254. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
W. A. Miller, D. J. Lewis, M. D. G. Pereira, M. Lennox, P. A. Conrad, K. W. Tate, and E. R. Atwill Farm Factors Associated with Reducing Cryptosporidium Loading in Storm Runoff from Dairies J. Environ. Qual., August 8, 2008; 37(5): 1875 - 1882. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. M. Butler, D. H. Franklin, M. L. Cabrera, A. S. Tasistro, K. Xia, and L. T. West Evaluating Aeration Techniques for Decreasing Phosphorus Export from Grasslands Receiving Manure J. Environ. Qual., May 1, 2008; 37(3): 1279 - 1287. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| The SCI Journals | Agronomy Journal | Crop Science | |||
| Journal of Natural Resources and Life Sciences Education |
Vadose Zone Journal | ||||
| Soil Science Society of America Journal | Journal of Plant Registrations | The Plant Genome | |||
). Because there were no significant differences in sediment and nutrient reduction between interrill and concentrated flow within grass barriers, graphs were not depicted for the corresponding treatments.