For more: http://www.extension.org/67683 Identifying time periods when land application of manure is likely to contribute to surface runoff contamination is important for making proper management decisions and reducing the risk of surface water contamination. Recently, a great deal of attention has been focused on reducing nutrient and sediment losses from the winter period. However, sediment and nutrient losses during the late spring period can be significant and it is important to understand landscape and weather conditions that lead to elevated runoff risk during this time period.

1. Using soil moisture to predict the risk of
runoff on non-frozen ground
Waste to Worth 2013
April 3rd
, 2013
Tim Radatz - Research Specialist, MN and WI Discovery Farms

2. Introduction
• Identifying critical high
risk runoff periods can
reduce environmental risk
• Understanding key
parameters influencing
the likelihood of runoff
generation

3. Objectives
Improve the understanding of the factors that influence
runoff generation in agricultural watersheds
1) Evaluate the influence of storm and landscape
characteristics on surface runoff generation
2) Determine critical thresholds for surface runoff
generation
1) Soil moisture
2) Rainfall Intensity

4. Methods and Materials
• Discovery Farms
Program (DFP)
– Direct plant tillage
– Surface residue 50-
65%
– Three year crop
rotation (Cg/Cs/S)
– Grass waterways and
broad-based terraces
– Tama soil series
– Mean slopes - 5%
http://uwdiscoveryfarms.org/

5. Methods and Materials
• Pioneer Farm (PF)
– Conventional tillage
• Fall - chisel plow
• Spring - soil finisher
– Surface residue 15-30%
– Seven crop year rotation
(C/C/C/O/A/A/A)
– Grass waterways and terraces
– Tama and Ashdale soil series
– Mean slopes – 5 to 7 %
– Farmstead area (2 ha) within PF7
http://www.uwplatt.edu/pioneerfarm

6. Storm Event Data
• Data include – precipitation depth and
intensity, runoff depth from each basin,
antecedent soil moisture (ASM), and crop cover
• Only storm events >2.5 mm
• Non-frozen ground periods 2004-2007

7. Runoff Characteristics
Study period runoff
• Lower number of runoff
events and runoff depth at
DFP
• %Precipitation as Runoff
– 0.9% DFP
– 2.0% PF (1.8% PF3 and PF5)
• Similar precipitation and
landscape characteristics
except for tillage strategies
and crop rotations
• Impervious surfaces located
within PF7
RunoffEvents
0
10
20
30
40
50
60
70
80
90
DF1 DF2 DF3 PF3 PF5 PF7
RunoffDepth(mm)
0
10
20
30
40
50
60

8. Soil Moisture Breakpoint
Analysis
• Runoff coefficient
(runoff/precipitation)
vs. antecedent soil
moisture
• Completed for each
basin
• Breakpoint regression
example

9. Soil Moisture Breakpoint
Analysis
• ASM threshold of
0.39 cm3
cm-3
• Above Threshold
– 16% of precipitation
– 78% of runoff depth
• Below Threshold
– Few runoff events
– Intense storm
events

10. Soil Moisture Breakpoint
Analysis

11. I30 Breakpoint Analysis
• Comparing runoff coefficients and storm
intensity (30 minute max)
– DFP and PF storm events were averaged and
combined
• Antecedent soil moisture groups
– ≤0.35, 0.35 to 0.40, and ≥0.40 cm3
cm-3
• Crop cover groups
– <50% and ≥50%

12. I30 Breakpoint Analysis
0 20 40 60 80 100
I30 (mm hr-1
)
0 20 40 60 80 100
0.0
0.1
0.2
0.3
0.4
RunoffCoefficient(mmmm-1
)
ThresholdI30:9mmhr-1
Slope Above Threshold: 0.007 hr mm
-1
ThresholdI30:6mmhr-1
Slope Above Threshold: 0.006 hr mm
-1
Antecedent Soil Moisture ≥0.40 cm3
cm-3
Crop Cover ≥50% Crop Cover <50%

13. I30 Breakpoint Analysis
Antecedent Soil Moisture 0.35 to 0.40 cm3
cm-3
Crop Cover ≥50% Crop Cover <50%

14. I30 Breakpoint Analysis
Antecedent Soil Moisture <0.35 cm3
cm-3
Crop Cover ≥50% Crop Cover <50%

15. Conclusions
• The ability to identify high risk periods is vital
• Soil moisture measurement can be an indicator
• Thresholds for runoff generation
– ASM
• 0.39 cm3
cm-3
• Above threshold: 16% of precipitation but 78% of
runoff
– I30
• Strongly influenced by ASM
• As ASM increased, I30 thresholds decreased

16. So What Does This Mean…
Important to think about moisture levels when
planning field operations – manure/fertilizer
and pesticide application, tillage
Too late! Planning for intermediate
moisture conditions
Source: http://www.tractorbynet.com

17. Questions?
Special Thanks To:
•Dr. Anita Thompson, Dr. Fred Madison, and Dr. Birl Lowery
•UW-Platteville Pioneer Farm
•UW Discovery Farms
•WI USGS
•Mark, Jan, and Joe Riechers