The California Department of Food and Agriculture (CDFA) Fertilizer Research and Education Program (FREP) Grant Program annually funds research projects related to the environmentally safe and agronomically sound use and handling of fertilizing materials in California.
The following project was recently completed and added to the FREP Research and Project Database.
Nitrogen Content of the Harvested Portion of Specialty Crops to Estimate Crop Nitrogen Removal and Improve Nitrogen Management in Crops

Project Locations: Commercial fields in Monterey, San Benito, Santa Clara and Ventura counties
Project Overview: Through the state’s Irrigated Lands Regulatory Program (ILRP), the Central Coast Regional Water Quality Control Board (CCRWQCB) requires farmers to calculate the nitrogen (N) left in the field after harvest to estimate N that is at risk for leaching into groundwater. ILRP recordkeeping requires a calculation of both the N applied through different types of fertilizers, crop amendments, and irrigation water, as well as N removed through crop harvest, incorporation into woody plant tissue, and other methods such as water treatment. N removal coefficients are an important tool for this calculation because they provide growers and Certified Crop Advisors with a simple, affordable method for estimating the N removed in the harvested portion of the crop. However, N removal coefficients can vary due to soil properties and management practices. Thus, it is important that these coefficients accurately reflect the range of growing conditions and production practices used by growers on the Central Coast.
Project Impact: The N removal coefficients developed in this project were shared with the CCRWQCB and Central Coast Water Quality Preservation Inc. (Preservation Inc.), which is a third-party group assisting growers to meet water quality regulations in the region. The values were incorporated into the dropdown menu used for filling out the Irrigation and Nutrient Management Plan (INMP) Summary Reports by Preservation Inc. and shared with growers and consultants. As a result, the new N removal coefficients were first used in the March 2024 INMP reporting to the CCRWQCB.
Click here to view a FREP Research Update blog for more details and the project’s final report.