Using soil moisture to predict the risk of runoff on non-frozen

ground

Waste to Worth 2013April 3rd, 2013

Tim Radatz - Research Specialist, MN and WI Discovery Farms

Introduction

• Identifying critical high risk runoff periods can reduce environmental risk

• Understanding key parameters influencing the likelihood of runoff generation

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

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/

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

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

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

Run

off E

vent

s

0

10

20

30

40

50

60

70

80

90

DF1 DF2 DF3 PF3 PF5 PF7

Run

off D

epth

(m

m)

0

10

20

30

40

50

60

Soil Moisture Breakpoint Analysis

• Runoff coefficient (runoff/precipitation) vs. antecedent soil moisture

• Completed for each basin

• Breakpoint regression example

Soil Moisture Breakpoint Analysis

• ASM threshold of 0.39 cm3cm-3

• Above Threshold– 16% of

precipitation– 78% of runoff

depth

• Below Threshold– Few runoff events– Intense storm

events

Soil Moisture Breakpoint Analysis

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 cm3cm-3

• Crop cover groups– <50% and ≥50%

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

Ru

noff

Co

effi

cie

nt (

mm

mm

-1)

Thr

esho

ld I3

0: 9

mm

hr-1

Slope Above Threshold: 0.007 hr mm-1

Thr

esho

ld I3

0: 6

mm

hr-1

Slope Above Threshold: 0.006 hr mm-1

Antecedent Soil Moisture ≥0.40 cm3cm-3

Crop Cover ≥50% Crop Cover <50%

I30 Breakpoint Analysis

Antecedent Soil Moisture 0.35 to 0.40 cm3cm-3

Crop Cover ≥50% Crop Cover <50%

I30 Breakpoint Analysis

Antecedent Soil Moisture <0.35 cm3cm-3

Crop Cover ≥50% Crop Cover <50%

Conclusions

• The ability to identify high risk periods is vital• Soil moisture measurement can be an indicator• Thresholds for runoff generation

– ASM • 0.39 cm3cm-3

• Above threshold: 16% of precipitation but 78% of runoff

– I30• Strongly influenced by ASM• As ASM increased, I30 thresholds decreased

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

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