Using Polymers to Reduce Sediment and Nutrient Losses from Central Coast Vegetable Fields

The Issue

Agricultural run-off from Central Coast vegetable fields carries sediments and nutrients into the tributaries that drain into the Monterey Bay National Marine Sanctuary, one of the largest ocean sanctuaries in the United States. The Central Coast Regional Water Quality Control Board, the agency that enforces state and federal water quality regulations, is requiring farmers to reduce the discharge of contaminants from agricultural fields into surface water bodies, such as streams, rivers, lakes and the ocean. In order to reach targets for clean water, growers will need to put in place affordable, conservation practices that minimize the impacts of farming on the health of aquatic environments.

What Has ANR Done?

Chemical polymers are long chained molecules that can be used to bind soil particles together so that soil is less likely to erode during irrigation and rain events. Farmers in the Northwest of the United States and in the San Joaquin Valley of California have successfully used small doses of the polymer, polyacrylamide (PAM), to control erosion when they apply water to the furrows between the crop rows. However, little information was available on how to use PAM with overhead sprinklers, the principal method of watering vegetables on the Central Coast. By conducting field trials in commercial fields and on research plots, UCCE Monterey County farm advisors were able to develop a practical method to inject PAM into sprinklers to minimize erosion from vegetable fields. Results of more than 10 field trials have shown that the injection of low concentrations of PAM (2.5 to 5 ppm) into the irrigation water reduced sediment levels in tail water by 90 percent on average. On some soil types sediment losses were reduced by 98 percent. Additionally, losses of phosphorus and nitrogen nutrients that are bound to sediments were reduced by 70 percent on average.

The Payoff

Use of PAM Reduces Sediment Levels in Tail Water by More Than 90 percent

The use of PAM is helping growers make dramatic progress in improving water quality. By retaining sediments in the fields, water in nearby creeks and rivers stays clear. By keeping soil nutrients, such as phosphorus and nitrogen from migrating into surface water, algal blooms are prevented and the health of aquatic environments can be maintained. Finally, growers have found that they can make significant strides in reaching water quality targets set by regulators and save money at the same time. Using PAM to stop irrigation-related erosion reduces annual costs of cleaning sediments out of drainage ditches and retention ponds.

Contact

Michael Cahn
Irrigation and Water Resources Advisor
UC Cooperative Extension, Monterey County
(831) 759-7350 - mdcahn@ucdavis.edu