Improving Agricultural Runoff Management for Irrigated Lands in

California

A. Ristow, S. Prentice, W. Wallender, W. Horwath

Department of Land, Air, and Water Resources University of California, Davis, California

Outline

Introduction SAFS Project Initial Runoff Research Current Water Quality

Research Results Recommendations

Introduction

Delta water resources are being stressed by population growth, climate, and competing land uses

Focus of Clean Water Act (1973) is shifting Loss of agricultural discharge waiver

pressuring growers (2003)

POINT SOURCE POLLUTION CONTROLS 19731973

TMDL MONITORING

20032003

Introduction

Farm-based conservation practices presently exist for reducing soil losses and runoff potential…

Winter Legume Cover Cropping (WLCC)

Reduced Tillage (RT) Systems

Sediment Traps

Introduction

…However, potential benefits and disadvantages for California’s unique agro-ecosystems are not well understood

Changes in water balance and management

Timing of Field Operations

Cost / Benefit analyses of WLCC and RT systems

Sustainable Agriculture Farming Systems (SAFS), UC Davis

SAFS Experimental Design 1986 - 2001

Agro-chemical based -representative of typical Central Valley system

CONVENTIONAL

LOW INPUT

ORGANICManaged according to CCOF guidelines - organic N from manure and WLCC

Intermediate system - Nitrogen from WLCC and some supplemental inorganic N; occasional herbicides

• Four year, three crop rotation

• Side-by-Side research plots

• Adaptive Management

• Collaborative research

SAFS Experimental Design 1986 - 2001

Runoff Infiltration and Soil Water Storage Using WLCC (1998-2000)

Determine a field’s ability to conserve water for subsequent crops

Evaluate the effects of soil physical conditions on the water balance

Rainfall, runoff, and soil water content data collected on Fallow and WLCC treatments

Objectives

Winter Runoff SAFS Research Plots

WLCC

Fallow

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CONVENTIONAL

LOW INPUT

ORGANIC

Precipitation

SAFS-Runoff as Percentage of Rainfall 1999-2000

1998 – 2000 Runoff Research Summary

Net runoff from CONV (winter fallow) test areas was consistently higher than WLCC and ORG

Soil moisture content was significantly higher in the WLCC system

WLCC can improve soil water storage for subsequent crops if it is destroyed before additional soil water is lost as evapotransporation

SAFS Experimental Design 2002 - Present

CONVENTIONAL

LOW INPUT

ORGANIC

Initial SAFS study led to expansion of parameters in 2002 and relocation to dedicated sustainable agriculture research facilities

SAFS Experimental Design 2002 - Present

CONVENTIONAL

LOW INPUT

ORGANIC

STANDARD TILLAGE

REDUCED TILLAGE

STANDARD TILLAGE

REDUCED TILLAGE

STANDARD TILLAGE

REDUCED TILLAGE

2003 – 2006 SAFSWater Quality Research

– Examine runoff quality and quantity – Tillage system comparisons– Use of grower-collaborator fields– Determine relationships between

cropping systems and TMDL discharge potential

2003 – 2006 SAFS Research

Quantify runoff from systems employing WLCC, RT, and sediment traps

Quantify nutrient, pesticide, and sediment concentrations of runoff from each system

Identify factors influencing runoff quality and soil water relations in the systems under study

Objectives

SAFS Controlled Research Plots - Winter 2003-2004

Runoff channeled through trapezoidal flume draining into a ditch at the end of plot

Portable sampler and data-logger collect data on runoff quantity

Water samples taken automatically at regular intervals during storm

Challenges To Monitoring

•Data collection was limited by several complexities during the first storm season

•Sampler was not designed for this scale of operation

•Small plot size and flat runoff surface produced negligible discharge from all research plots

•The natural variation associated with agro-ecosystems is an important factor to consider when monitoring for water quality

Rainfall Simulation

Attempts To Overcome Challenges

• Installed stilling well to overcome “noise” in data readings

• Rainfall simulation exercise to determine minimum rainfall needed to generate runoff

Installation of Stilling Well

Grower-Collaborator Fields Winter 2003 – 2004

•Negligible data from SAFS research plot for 2003-2004

•However, 2003–2004 data collection from grower fields was effective

•Growers were added for 2004 – 2005 season

•Additional growers will provide information on RT systems for 2004 - 2005

Installing Runoff Collection Sumps at SAFS Research Site

Winter 2004-2005

Collection Sump

Data logger

Catchment

Collection Sump

Data logger

Catchment

Collection Sump

Data logger

Catchment

•Stilling wells and rain simulation not reliable

•Research team went to use of collection sumps for 2004 – 2005

−This change has provided useful data (Analysis pending)

Grower-CollaboratorField Site Description

From left to right: Winter Fallow field (NCC), Sediment Trap treatment (PST), and a Winter Cover-Cropped field (CC) located at Rominger Brothers Farm in Yolo County.

Methods

Large-scale comparisons of alternative vs. conventional practices from local growers

Discharge measured with an area-velocity (AV) sensor placed in bottom of main drainage ditch leaving field

Data-logger / auto-sampler and rain gauge take readings and samples at pre-programmed intervals

Methods continued

Discharge is measured and sampled at regular intervals during all runoff events…

…then collected and transported to UCD for water quality analyses:

– Sediment– Nitrate (NO3

-), Ammonium (NH4

+), Phosphate (PO4-)

– Dissolved Organic Nitrogen, Phosphorus, and Carbon (DON, DOP, DOC)

– Pesticides

Winter 2003 – 2004

Summer 2004

Results From Grower Fields

Discharge Hydrograph Comparing Non-CC and CC

FieldsEarly Storm Season

(December 29th, 2003)Late Storm Season

(February 25th, 2004)

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3AM25 Wed Feb 2004

6AM 9AM 12PM 3PM 6PM 9PM 26 Thu 3AM 6AM 9AM 12PM 3PM

25-26 February 2004

m3smm

2/25/2004 2:00:00 AM - 2/26/2004 4:00:00 PM

Cover Cropped (133.723 m3) Non Cover Cropped (912.445 m3) Precip (52.7 mm)

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12/29/2003 3:00:00 AM - 12/29/2003 9:00:00 PM

Cover Cropped (58.015 m3) Non Cover Cropped (246.951 m3) Precip (49.7 mm)Precip.

NCCCC

mm3 / s

mm

Discharge Comparisons

Winter 2003 -2004 Discharge

16.3%0.52m/s

0.9%Total Winter Precipitation Discharged as Runoff

Average Peak Runoff Velocity

NCC CC 

0.24m/s

Summer 2004 Discharge*NCC  CC

Total Discharge

30,385 m3 19,150 m3

*Total input not measured

Load of Constituents

P DOP NO3-N NH4-N DON DOC

January 1st, 2004 February 25th, 2004

g / event / acre

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P DOP NO3-N NH4-N DON DOC

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Sediment Load

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/ ev

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TSS

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Concentration

PPM

Winter 2003 -2004 Runoff Summer 2004 Runoff

NCC Sediment Trap CC

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P NO3-N NH4-N DOP DON DOC

Results

SS (mg / L)

Tur

bidi

ty

(N

TU

)

Relationship between Suspended Solids (SS) and Turbidity

Winter 2003 – 2004

y = 0.6305x + 199.14

R2 = 0.7956

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Summary of Results:Winter 2003 - 2004

Winter fallow field discharged eighteen times more runoff than WLCC field

Average peak runoff velocities from fallow field were twice as high as WLCC field runoff

Use of sediment trap significantly reduced phosphate, NO3, NH4, dissolved organic P and N concentrations from fallow field runoff

Summary of Results:Winter 2003 - 2004

Significantly lower concentrations for Phosphate, NH4, organic N, and Turbidity in WLCC field compared to Fallow field

Concentrations for all fields were low Cover Cropping appears to greatly

minimize sediment loads and other non point source pollutants (NPSP)

Summary of Results:Summer 2004

Following winter CC, concentrations of most water quality constituents were significantly higher than winter fallow runoff concentrations

Recommendations

Alternative management practices have potential to reduce winter and summer discharge

These practices may:– Minimize Sediment loads– Mitigate agro-chemical pollution in California

Agriculture– Assist water coalition groups in meeting watershed

TMDL goals

Recommendations

Conceptual models must be developed

– Correlate water inputs and load reductions with alternative agricultural management practices

Agricultural contribution to NPSP may lie within acceptable drinking water quality standards

However there may be ecological significance to NPSP that has yet to be determined

Concern?

In Summer, field scale water balance may be affected following winter CC. The pros and cons must be examined.

Our Questions

How do field configurations (e.g., size, length of run) affect infiltration, runoff energy, and NPSP discharges?

Your Questions…

?