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Reduce pollution with proper fertilizer timing
The Issue
Applying nitrogen and phosphorus with irrigation water is a common practice in the Imperial Valley. If the fertilizers are applied incorrectly, the nutrients end up in the drains rather than in the crop. Nitrogen and phosphorus are the two main nutrients that cause eutrophic conditions (high algal biomass and low dissolved oxygen concentrations that cause massive fish kills) in the Salton Sea.Current and proposed federal water quality standards for California require growers to improve the quality of drainage waters. To achieve both federal and state water quality objectives, growers will have to reduce the amount of phosphorus that reaches the drains and the Salton Sea.
What Has ANR Done?
UCCE Imperial County advisors evaluated various lettuce irrigation and fertilizer application practices on (1) basin irrigation systems (0 percent slope and 0 percent runoff) and (2) free-draining graded furrows (1.5 percent slope and normal runoff). We compared various water flow rates and the timing of fertilizer applications.We developed a relationship between water application rates and the amount and rate of fertilizer applications. We then developed recommendations on the amount and duration of fertilizer applications during irrigation events for each irrigation method.
The Payoff
Irrigation management improves fertilizer use efficiency and water quality
The UCCE advisors' recommendations (Best Management Techniques or BMTs) are being adopted by growers. This is improving fertilizer use efficiency and reducing the non-point source pollution in the Salton Sea watershed. Our educational materials also are used to implement plans to meet the TMDL (Total Maximum Daily Load) regulations. Irrigation management is a key factor in controlling the concentration and the load of phosphorus in runoff water. Reducing the rate of surface runoff during and after phosphorus application events could reduce phosphorus load in surface waters by as much as 75 percent compared to standard irrigation practices. Our BMTs were included in the Regional Water Quality Control Board (Region 7) silt/sediment TMDL standards. For additional information, please visit SWRCB success story website: http://www.waterboards.ca.gov/water_issues/programs/nps/success.shtml