Rainfall simulations were conducted within mixed (cool- and native warm-season) grasslands in the sloping, rocky soils typical of the Ozark Mountains region to estimate nutrient and bacteria levels in runoff from biosolids and mineral fertilizer (MF). The ability of narrow (1 m) vegetated filter strips (VFS) to reduce losses was evaluated. Experiment 1 included an untreated control (C); 37 kg plant available nitrogen (PAN) ha−1 from biosolids applied to the upslope half of the plot with the downslope half serving as a VFS (LBF); 74 kg PAN ha−1 from biosolids, with VFS (HBF); and a uniform biosolids application at the lower rate and no VFS (LBU). Experiment 2 examined runoff from MF applied at 89 kg ammoniacal nitrogen (NH4-N) ha−1 and 147 kg phosphorous (P) ha−1 over the whole plot (MFW) or only on the upslope half (with VFS) (MFF). No significant differences were detected among mean fecal coliform levels despite large differences in magnitude. Losses of NH4-N and P were greater for LBU than for LBF. Although only marginally significant (
An estimated 226,800 dry tonnes of biosolids are produced each year in Missouri where 60% of the sludge is incinerated and 30% is applied to agricultural land [
A considerable body of research has confirmed the potential for losses of nutrients such as nitrogen (N) and phosphorus (P) from agricultural fertilizers applied to fields [
Management practices that can potentially influence nonpoint source pollution levels and water quality include a shift in fertilizer time of application and the use of vegetated filter strips (VFS) to reduce contaminant content. In central and southern Missouri nearly two-thirds of cool-season forage production occurs in spring. Consequently, some producers have shifted fertilizer, manure, or biosolids application to late summer in an effort to increase autumn production either for hay harvest or winter grazing (M. Green and M. Kennedy, pers. comm.). VFS have proven effective in reducing sediment [
The following two experiments were conducted to provide additional data on fertilization management and VFS efficacy on grassland typical of the Ozarks region (i.e., sloping, rocky soils). The biosolids experiment evaluated and compared sediment, nutrient, and bacteria levels found in runoff from biosolids applications with or without a VFS. Biosolids were applied at PAN levels typically applied to native warm-season grasses. The mineral fertilizer experiment investigated the efficacy of a narrow VFS in reducing sediment, nutrient, and bacteria pollutant loads.
Rainfall simulations were conducted from August 2009 to October 2009 on field plots with a Nixa very gravelly silt loam (loamy-skeletal, siliceous, active, mesic Glossic Fragiudults) in Lawrence County, Missouri. Vegetation in plots consisted of a mixture of cool- (especially
Surface runoff plots 1.50 × 2.00 m (long axis oriented downslope) had metal borders 5 cm above and below ground level in order to isolate runoff. Each experiment was conducted with four replicates. The plots were mowed to a height of 10 cm 7 to 10 days prior to rainfall simulations and had similar vegetative cover conditions. A full replication of each experiment was carried out on each of 4 days (Table
Mean volumetric soil moisture, percent vegetative cover, and mean runoff volume from each of the four blocks used in this study.
Date | % Volumetric soil moisture | % Vegetative cover | Mean runoff volume (L) |
---|---|---|---|
Aug. 20, 2009 | 39.1 | 84.4 | 57.1 |
Aug. 27, 2009 | 19.6 | 93.8 | 25.4 |
Sep. 03, 2009 | 24.3 | 88.8 | 14.6 |
Oct. 13, 2009 | 46.7 | 97.2 | 80.2 |
Portable rainfall simulators [
Samples were labeled with a randomly assigned reference number, stored in ice water, and delivered to the Southwest Water Treatment Plant in Springfield, Missouri, within 7 h of collection for stabilization and analyses. Analyses were completed for total suspended solids (TSS), total Kjeldahl nitrogen (TKN), dissolved total Kjeldahl nitrogen (DTKN), NH4-N, dissolved ammoniacal nitrogen (DNH4-N), nitrate nitrogen (NO3-N), TP, dissolved phosphorus (DP), and fecal coliform colony-forming units (CFUs) levels. TSS, NH4-N, and CFUs were determined according to standard biosolids protocols [
Gutters in plots were sealed with a bentonite/soil mixture and were washed of free soil and clay before the rainfall simulations were initiated. Percent ground cover was measured by the line-transect method (3 transects and 10 observations per transect in each plot), and mean volumetric soil moisture (
The four treatments included untreated control (C); 1664 kg ha−1 low rate of biosolids with a 1 m vegetative filter (LBF); 1664 kg ha−1 low rate of biosolids, unfiltered (LBU); 3328 kg ha−1 high rate of biosolids with a 1 m vegetative filter (HBF). PAN and TP values for these treatments are given in Table
Plant available nitrogen (PAN) and total phosphorus (TP) included in mineral fertilizer and biosolids treatments.
Constituent | LB† | HB | MF |
---|---|---|---|
Kg ha−1 | |||
PAN‡ | 36.8 | 73.6 | 89.3 |
TP | 58.3 | 116.6 | 146.9 |
The anaerobically digested, dewatered municipal biosolids used in this study were Class B biosolids [
A blend of triple superphosphate and diammonium phosphate served as the MF in the second experiment. Plots received no amendment (untreated control; C), 89.3 kg ammoniacal nitrogen (NH4-N) ha−1 and 146.9 kg P ha−1 as a blend of MF applied to upslope half (1 m) of the plot which was “filtered” by the downslope 1 m of the plot which served as a vegetative filter strip (MFF), or an identical rate of blended mineral fertilizer spread over the whole plot (MFW). Therefore, the plots were equal in total area, but the MFW treatment received twice as much fertilizer on a plot area basis. With this design we intended for the MFF treatment to simulate grassland bordered by a narrow span of vegetation that could serve as a buffer to a protected water body, slope change, or area of concentrated flow, whereas the MFW treatment would represent a landscape that received uniform fertilization up to the edge of an unprotected (no VFS) critical area.
Because structured treatment levels (i.e., high rate of biosolids treatment was double that of low rate of biosolids treatment) violate an assumption of analysis of variance (ANOVA), the C and biosolids treatment effects from the biosolids experiment were assessed by curve-fitting [
Mean fecal coliform CFUs concentrations ranged from about 100 (C) to nearly 36,000 (LBU) CFUs per 100 mL (Table
Concentration and total fecal coliform colony-forming units (CFUs) in runoff.
Treatment† | Mean CFUs in 100 mL | Mean total CFUs‡ |
---|---|---|
LBU | 35,720 | 10,965,563 |
LBF | 7,080 | 1,348,587 |
HBF | 4,880 | 367,700 |
C | 117 | 90,130 |
Mean fecal coliform colony-forming units (CFUs) concentrations in runoff from control (C); low rate of biosolids, filtered by a 1 m grass strip (LBF); low rate of biosolids, unfiltered (LBU); and high rate of biosolids, filtered by a 1 m grass strip (HBF). CFU level in runoff was not well described by application rate (slope
Preplanned orthogonal contrasts and linear regression were used to compare and isolate aspects of this study. No differences could be declared among biosolids treatments for TSS in runoff. This result could be expected if biosolids are relatively rainfast and have a relatively low impact on altering sediment runoff levels. However, Harris-Pierce et al. [
Untransformed treatment means for all analyzed biosolids nutrients in runoff from Experiment
Contaminant | C | LBF | LBU | HBF |
---|---|---|---|---|
Kg ha−1 | ||||
TSS† | 15.7 | 12.0 | 37.0 | 10.3 |
TKN | 1.10 | 0.67 | 3.33 | 9.00 |
DTKN | 0.33 | 0.77 | 1.67 | 8.67 |
NH4-N | 0.07 | 0.47 | 2.07 | 0.93 |
DNH4-N | 0.07 | 0.47 | 2.10 | 0.87 |
NO3-N | 0.03 | 0.02 | 0.07 | 0.03 |
TP | 0.10 | 0.13 | 0.33 | 0.23 |
DP | 0.07 | 0.10 | 0.23 | 0.13 |
Total suspended solids (TSS), total phosphorus (TP), and dissolved phosphorus (DP) loading in response to TP application rate for C, LBF, and HBF.
Total ammoniacal nitrogen (NH4-N), dissolved ammoniacal nitrogen (DNH4-N), and nitrate nitrogen (NO3-N) loading in response to plant available nitrogen (PAN) application rate for C, LBF, and HBF.
In a separate analysis, C was compared to total nutrient runoff from the MF treatments. MFF loading did not differ from MFW for any factor according to the protected LSD mean separation procedure (
Untransformed treatment means for all analyzed mineral fertilizer nutrients in runoff from Experiment
Contaminant |
|
MFF | MFW |
---|---|---|---|
Kg ha−1 | |||
TSS | 15.6a‡ | 17.6a | 5.7a |
TKN | 1.1b | 5.9ab | 16.7a |
DTKN | 0.33b | 5.4ab | 16.4a |
NH4-N | 0.067b | 5.4ab | 15.7a |
DNH4-N | 0.067b | 5.4ab | 15.6a |
NO3-N | 0.033b | 0.2ab | 0.4a |
TP | 0.10b | 5.4ab | 18.9a |
DP |
0.07a | 1.5a | 13.9a |
These results suggest that even an undersized VFS can reduce certain nutrients when compared to fertilizer applications made without any VFS. DTKN and DNH4-N were dominant components of TKN and total NH4-N values in runoff among all treatments. This result was expected from soluble mineral fertilizer salts and resulted in nearly identical trends among these parameters.
Statistical analysis of fecal coliform in runoff was obscured by variability and perhaps made worse by historical or accidental contamination of plots. However, that the biosolids treatment LBU numerically had the highest mean concentration and total runoff of coliform is noteworthy. In the LBF versus LBU contrast, differences suggest that even a small VFS is capable of decreasing biosolids nutrient levels in runoff when compared to unfiltered runoff. Biosolids applications in the state of Missouri, however, require much wider buffer areas (15.2 to 91.4 m) than those used in these experiments [
MFF and MFW did not differ in any of the orthogonal contrasts. However, it is important to notice that, except for TSS, MFW always differed from the C according to a protected LSD test (
Mineral fertilizer
Colony-forming units
Dissolved ammoniacal nitrogen
Dissolved phosphorus
Dissolved total Kjeldahl nitrogen
Ammoniacal nitrogen (total)
Nitrate nitrogen
Plant available nitrogen
Total Kjeldahl nitrogen
Total phosphorus
Total suspended solids.
The authors declare that there is no conflict of interests regarding the publication of this paper.