RCD Ag Water Project Yields Benefits for Farmers and the Delta

 

The declining health of the Delta Ecosystem has recently been the topic of many articles and discussions. In the past two years the Contra Costa Resource Conservation District (CCRCD) has worked with several farmers who stepped forward to “do their bit” to help the Delta, and at the same time, improved their crop production.  This year, the results from pilot projects implemented by these farmers were very promising ─not only for improving Delta water quality, but also for the farmers’ crops.

 

Program Description         Benefits to Farmers         Water Quality Improvement            The Future

 

The Program:  The CCRCD reached out to growers who traditionally furrow irrigate their row crops, primarily processing tomatoes and sweet corn.  Since furrow irrigation often discharges large quantities of muddy “tailwater,” that may be directed into Marsh Creek, or Discovery Bay and eventually back into the Delta, tailwater is seen as one possible source of pollution, as well as contributing to the loss of good topsoil.

 

The State Water Resouces Control Board created an Agricultural Water Quality Grant Program (AWQGP) to help farmers reduce or eliminate irrigation tailwater and/or stormwater runoff.  The CCRCD obtained funding from this program and worked with local farmers to develop five project sites totaling 335 acres where techniques called “beneficial management practices (BMPs)” were implemented.  Two of the growers with larger parcels converted from furrow irrigation to surface drip irrigation on their processing tomato fields.  The surface drip systems used drip tape placed on the surface of the furrows or, in some cases, in every other furrow.  Irrigation water and nutrients were disbursed via the drip tape, allowing for a more direct application to the plants’ root zone.  (This method is also sometimes used to apply liquid fertilizer.)

 

Benefits to Farmers:  Besides benefiting water quality (discussed below) the drip irrigation systems resulted in a more uniform distribution of water and cost savings due to less water being applied.  Crop yield increases ranged from 24% to 70% in four fields.  The drip irrigated fields had fewer weeds, resulting in a labor cost savings to growers.  Reduced maintenance of field ditches and tail water collection pits (which are used with furrow irrigation) also increased labor savings and benefited the growers.  

 

Economic Benefits of Drip Irrigation

(on one 144 acre field for a whole irrigation season)

Water Usage

Water Cost Savings

Weeding Costs Savings

Ditch Maintenance Costs Savings

Total Cost Savings

Decreased by 290 acre feet

$5800

$7200

$3000

$16,000

 

Water Quality Improvements: To measure the effectiveness of the drip systems, the CCRCD monitored water quality at the drip irrigated projects sites, and at nearby furrow irrigated fields.  Tailwater samples were compared for concentrations of analytes, such as Total Organic Carbon (TOC), Total Suspended Solids (TSS) or sediments, pH, and Specific Conductance (or salts)..

 

The obvious difference between the furrow irrigated fields and the drip irrigated fields was the significantly reduced volume of tailwater discharged from the drip irrigated fields.  Tailwater on the drip irrigated fields was typically non-flowing water, less than an inch deep, at the end of a furrow. During the midday heat no tailwater was discharged from the fields.  Not surprisingly, the water quality measurements showed the drip irrigated fields had much lower TSS values [High TSS (turbidity) in water may also mean higher concentrations of bacteria, nutrients, pesticides and metal, as these pollutants may attach to sediment particles and be carried into water bodies].

 

                               Total Suspended Solids (Water Turbidity)

15 to 69 mg/ L
 

2800 mg/L
 

440 mg/L
 

 

Total Organic Carbon, pH, and Specific Conductance did not vary significantly and even increased slightly at some drip irrigated sites when single grab samples were taken  (The volume of water flowing off a field would also need to be measured to evaluate pollutant load reductions).  Some constituents, such as TOC and salts, could become more concentrated in the relatively little tailwater generated by surface drip irrigation systems. 

 

The Future:  The success of the surface drip irrigation systems from last year spilled over to this year.  Two additional projects, an additional 131 acres, became part of the program in 2007.  A drip irrigation system was installed on 95 acres of processing tomatoes and 36 acres of sweet corn.  Water quality monitoring has been conducted, but the analytical results were not yet available for this Annual Report.  Although the water quality numbers are not yet known, both growers are pleased with the systems and with the vitality of their crops as of this report date.

 

From a water quality standpoint, it does not get any better than a preliminary observation at the corn field – no tailwater discharge.  With no runoff at all, no water sample collection was necessary.

 

The Contra Costa RCD greatly appreciates the assistance of the Natural Resources Conservation Service and the University of California Cooperative Extension for help with outreach and education for this project. Most importantly, we sincerely thank the growers who participated in this program. As some of the larger growers in the county, they have made a good faith effort to improve surface water quality by significantly reducing or eliminating tailwater discharges.  These efforts  will benefit the Delta ecosystem as a whole.