vegetative buffer strips for reducing herbicide
DESCRIPTION
69th SWCS International Annual Conference “Making Waves in Conservation: Our Life on Land and Its Impact on Water” July 27-30, 2014 Lombard, ILTRANSCRIPT
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R. N. Lerch1, C. H. Lin2, K. W. Goyne3, R. J. Kremer1, and S. H. Anderson3
Vegetative Buffer Strips for Reducing Herbicide Transport in Runoff:
Effects of Season, Vegetation, and Buffer Width
1USDA-ARS, Cropping Systems and Water Quality Research Unit, Columbia, MO2 Center for Agroforestry, University of Missouri
3Department of Soil, Environmental and Atmospheric Sciences, University of Missouri
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Rationale and Objectives• Rationale:
– The ability of vegetative buffer strips (VBS) to reduce the transport of herbicides has not been evaluated for high runoff potential soils such as those in the Central Claypan Region of northeastern Missouri.
– Data to needed to support design criteria for implementation relative to contaminant of interest, choice of grass species, and buffer width
• Objectives:1) Assess the effects of season, vegetation, and buffer width on runoff
transport of herbicides 2) Develop design criteria for buffer widths3) Assess soil quality in the buffers since their implementation in 2002.
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Study Location
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• Plot Layout– Mexico silt loam, 5% slope, eroded– Twelve 1.5 m by 16 m plots (4 treatments
replicated 3 times)• Experimental Design
– Grass treatments (3 reps/treatment):1) Tall fescue (TF); 2) Tall fescue with a switchgrass hedge (Hedge +
TF)3) Warm-season grasses (mainly eastern
gamagrass and indian grass) (Native)4) Continuous cultivated fallow (Control)5) Poplar trees + Native grasses (Tree)
– Buffer width Runoff collectors at: -1 m; 1 m, 4m, and 8m
– Seasons (2 reps/trt) – Spring, Summer, Fall• Herbicides (rate, kg/ha)
– Atrazine (2.2), glyphosate (1.5), and metolachlor (1.7)
Materials and MethodsExperimental Design
8 m
1.0 m
4 m
Slope(5%)
Fescue
Runoff sampling troughs
Fescue
T1
Native
T2 T3 T4
TilledArea
Switchgrass hedge width is 0.7 m
8 m
TilledArea
TilledArea
TilledArea
TilledArea
1.5 m
1 M
4 M
Source Area-1 M
8 M
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Materials and MethodsExperimental Design – Vegetation Treatments
Control
Tall Fescue
Native
Hedge + Tall Fescue
Tree-Grass
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• Plot Preparation– 1.5 m by 8 m area above the VBS was roto-tilled to ~10 cm
(source area)– Plots brought to saturation 24 hours before runoff collection– Herbicides broadcast with a backpack sprayer 16 hours before
runoff collection (not incorporated)• Runoff Collection
– Rainfall rate = 50 mm hr-1
– Collected beginning with initiation of flow at the 8 m sampler– Collected every 10 minutes for 60 minutes; composited to create
one sample for each buffer width (i.e., -1, 1, 4, and 8 m)• Runoff Sample Analyses
– Water and sediment analyzed for herbicides– Suspended sediment
• Soil Quality Assessments– Soil samples collected in May 2011– Enzyme activities – dehydrogenase, β-glucosidase, and
fluorescein diacetate hydrolysis (0-10 cm)– Atrazine degradation – 56 day incubations (0-10 cm)– Saturated hydraulic conductivity (0-10 cm and 10-20 cm)
Materials and MethodsExperimental Design
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• Relative Load−Normalized Load = contaminant mass at each
sampling position normalized to the total mass at the -1m samplers (input)
• Statistics− 3-way ANOVA for runoff data Factors - Season, Vegetation, Width PROC Mixed procedure with repeated measures Significance level, α = 0.05 PDIFF for LS mean comparisons
– 1-way or 2-way ANOVA for soil quality data Significance level, α = 0.05 F-LSD0.05 for mean comparisons
Materials and MethodsComputations and Statistics
-1m(Input)
1m 4m 8m
X X X XC1 C2 C3 C4
M1 M2 M3 M4M1/M1 M2/M1 M3/M1 M4/M1
( N o r m a l i z e d t o I n p u t )
Q1 Q2 Q3 Q4
– Non-linear regression used to correlate relative load reduction to buffer width General form of the 1st-order decay equation: y = a + be-kx
y = relative load; x = buffer width;k – rate constant; a,b – model coefficients
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ResultsRainfall
Error bars indicate +/‐SD
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ResultsRunoff
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ResultsRunoff
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ResultsAbsolute and Relative Loads
Error bars indicate +/‐SD
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ResultsInput Normalized Loads
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ResultsVegetation X Season Interactions
Atrazine Metolachlor
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ResultsDissolved vs Sediment-Bound
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ResultsGlyphosate - Dissolved vs Sediment-Bound
47%
36%
27%24%
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ResultsLoad Reductions as a Function of Buffer Width
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ResultsLoad Reductions as a Function of Buffer Width
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Grass Buffer DesignAnticipated Field‐Scale Results
Collecting runoff samples Drainage to Buffer Area Ratio8:1 2:1 1:18:0
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Results – Runoff ExperimentsMechanisms for Reducing Transport
• Infiltration– Runoff volume reductions: 62% for TF 54% for Hedge+TF 54% for Native 7-8% reduction per meter of buffer
• Sediment Trapping– Sediment load reduced by: 88% for TF 85% for Hedge+TF 80% for Native ~10% reduction per meter of buffer
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Soil Quality Assessments
Degradation of contaminantsMicrobial activitySoil hydrologic propertiesSorption Properties
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Atrazine Degradation
Statistical Differences
Vegetation Treatment
Control TF Hedge+TF Native Tree
Atra
zine
Rem
aini
ng o
r Min
eral
ized
(%
of A
pplie
d)
0
1
2
3
4
5
10
15
20
25
30
Atra
zine
Hal
f-Life
(day
s)
0
2
4
6
8
10
12
14Atrazine RemainingAtrazine Mineralized Half-Life
a a aa
a
a b b b b
a a a b ab
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Soil Enzyme Activities
Control TF Hedge+TF Native Tree
Act
ivity
(nm
ol o
r m
ol g
-1h-1
)
0.0
0.2
0.4
0.6
5.0
10.0
15.0
20.0Glucosidase Dehydrogenase FDA
a abb b b
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Hydraulic Conductivity
Treatment differences within a depth were NS Species by Depth interaction was NS
Control TF Native Tree Depth Means
Ksa
t (m
m h
r-1)
0
50
100
150
200
250
300
350 0-10 cm10-20 cm
a
b
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Summary and ConclusionsWater Quality• Vegetation treatment ‐ highly significant Load reductions in the range of 60‐90% for the vegetated treatments
• Buffer width – highly significant Exponential decrease in load with increasing width for the vegetation treatments
• Season – minor effect Only Hedge+TF treatment showed an effect for atrazine and metolachlor in summer
• Buffer Design Regression equations provide practical design criteria – accounts for contaminant, drainage‐to‐buffer area ratios, and vegetative cover type Potentially achieve desired reductions with less land taken out of production
Soil Quality• After 9 years, VBS had minimal effect on microbial activity or soil hydrologic properties
• Microbial adaptation to atrazine common in all treatments – t1/2 = 4.5 to 9.7 d