Improving Agricultural Runoff Management for Irrigated Lands in California

1. 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

2. Outline • Introduction • SAFS Project • Initial Runoff Research • Current Water Quality Research • Results • Recommendations

3. 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 TMDL MONITORING 1973 2003 Introduction

4. Farm-based conservation practices presently exist for reducing soil losses and runoff potential… Introduction • Winter Legume Cover Cropping (WLCC) • Reduced Tillage (RT) Systems • Sediment Traps

5. 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

6. Sustainable Agriculture Farming Systems (SAFS), UC Davis

7. SAFS Experimental Design 1986 - 2001 Agro-chemical based -representative of typical Central Valley system CONVENTIONAL Intermediate system - Nitrogen from WLCC and some supplemental inorganic N; occasional herbicides LOW INPUT Managed according to CCOF guidelines - organic N from manure and WLCC ORGANIC

8. SAFS Experimental Design 1986 - 2001 • Four year, three crop rotation • Side-by-Side research plots • Adaptive Management • Collaborative research

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

10. Winter Runoff SAFS Research Plots Fallow WLCC

11. SAFS-Runoff as Percentage of Rainfall 1999-2000

12. 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 1998 – 2000 Runoff Research Summary

13. SAFS Experimental Design 2002 - Present CONVENTIONAL Initial SAFS study led to expansion of parameters in 2002 and relocation to dedicated sustainable agriculture research facilities LOW INPUT ORGANIC

14. SAFS Experimental Design 2002 - Present STANDARD TILLAGE CONVENTIONAL REDUCED TILLAGE STANDARD TILLAGE LOW INPUT REDUCED TILLAGE STANDARD TILLAGE ORGANIC REDUCED TILLAGE

15. Examine runoff quality and quantity Tillage system comparisons Use of grower-collaborator fields Determine relationships between cropping systems and TMDL discharge potential 2003 – 2006 SAFSWater Quality Research

16. 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

17. 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 SAFS Controlled Research Plots - Winter 2003-2004

18. 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

19. Installation of Stilling Well 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

20. 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

21. Installing Runoff Collection Sumps at SAFS Research Site Winter 2004-2005 • 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)

22. 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. Grower-CollaboratorField Site Description

23. 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

24. 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

25. Results From Grower Fields • Winter 2003 – 2004 • Summer 2004

26. CC NCC Precip. mm3 / s mm Discharge Hydrograph Comparing Non-CC and CC Fields Early Storm Season (December 29th, 2003) Late Storm Season (February 25th, 2004)

27. 0.24m/s Summer 2004 Discharge* NCC CC NCC CC Total Winter Precipitation Discharged as Runoff Average Peak Runoff Velocity Total Discharge 30,385 m3 19,150 m3 16.3% 0.9% 0.52m/s Discharge Comparisons Winter 2003 -2004 Discharge *Total input not measured

28. NCC CC 80 70 g / event / acre 60 50 40 30 20 10 0 P DOPNO3-NNH4-NDONDOC Load of Constituents January 1st, 2004 February 25th, 2004 P DOPNO3-NNH4-NDONDOC Late Storm Season Early Storm Season

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

30. Concentration NCC Sediment Trap CC Winter 2003 -2004 Runoff Summer 2004 Runoff PPM

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

32. 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

33. 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)

34. Summary of Results:Summer 2004 • Following winter CC, concentrations of most water quality constituents were significantly higher than winter fallow runoff concentrations

35. 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

36. 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

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

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

39. Your Questions… ?