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 1973 TMDL MONITORING 2003

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 Agro-chemical based - representative of typical Central Valley system CONVENTIONAL LOW INPUT ORGANIC Managed 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

Runoff Infiltration and Soil Water Storage Using WLCC ( ) 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

SAFS-Runoff as Percentage of Rainfall

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 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 Present CONVENTIONAL LOW INPUT ORGANIC STANDARD TILLAGE REDUCED TILLAGE STANDARD TILLAGE REDUCED TILLAGE STANDARD TILLAGE REDUCED TILLAGE

2003 – 2006 SAFS Water 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  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 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

Installing Runoff Collection Sumps at SAFS Research Site Winter 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-Collaborator Field 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 (NO 3 - ), Ammonium (NH 4 + ), Phosphate (PO 4 - ) – 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 Fields Early Storm Season (December 29th, 2003) Late Storm Season (February 25th, 2004) Preci p. NCCCC mm3/smm mm3/smmm

Discharge Comparisons Winter Discharge 16.3% 0.52m/s 0.9% Total Winter Precipitation Discharged as Runoff Average Peak Runoff Velocity NCCCC 0.24m/s Summer 2004 Discharge* NCC CC Total Discharge 30,385 m 3 19,150 m 3 *Total input not measured

Load of Constituents P DOP NO3-N NH4-N DON DOC January 1 st, 2004February 25 th, 2004 g / event / acre NCCCC P DOP NO3-N NH4-N DON DOC Early Storm Season Late Storm Season

Sediment Load Kg / event / acre TSS January 1 st, 2004February 25 th, 2004 Early Storm Season Late Storm Season

Concentration PPMPPM Winter RunoffSummer 2004 Runoff NCCSediment TrapCC

Results SS (mg / L) Turbidity (NTU) Relationship between Suspended Solids (SS) and Turbidity Winter 2003 – 2004

Summary of Results: Winter 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, NO 3, NH 4, dissolved organic P and N concentrations from fallow field runoff

Summary of Results: Winter Significantly lower concentrations for Phosphate, NH 4, 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… ?