Highlights

• We reviewed the scientific literature for data on nitrogen concentrations in harvested crop parts
• We analyzed a large number of samples from California fields and orchards for total N in the harvested plant parts
• The results were summarized in two reports

The Team

Daniel Geisseler, Makena Savidge, Edward Turk

Background

The ratio of nitrogen applied to N removed is a key metric in the Central Valley Irrigated Lands Regulatory Program (CVILRP). Growers report applied N and yield to agricultural water quality coalitions. The coalitions in turn convert yield to nitrogen removed from fields and report various statistics to the Central Valley Regional Water Quality Control Board. For these calculations, reliable values of nitrogen concentrations in the harvested parts and perennial tissues of crops are needed.

Objectives

The objective of this project is to generate a robust dataset of nitrogen concentrations in harvested parts and perennial tissues of crops grown in California.

Our Approach

During the first phase of the project, we mined the scientific literature for data on nitrogen concentrations in harvested crop parts with an emphasis on California data. More than 70 commodities were included in the report, which was released in December 2016. For many commodities, a robust dataset of recent samples from California was not available. Based on the report, the crops in need of better data were identified.

During the second phase of the project, we collaborated with John Dickey and his team at the Southern San Joaquin Valley Management Practices Evaluation Program, who collected a large number of samples from fields across the Central Valley. We then processed these samples and analyzed them for total nitrogen by the dry combustion method. The results for nine crops were summarized in a first update of the report, which was released in March 2021. The crops included were carrots, silage corn, peaches, pistachios, plums, pomegranates, sunflower, safflower, and processing tomatoes. In addition, recently published data for cotton and walnuts were included.

Results

The results of the literature review and the laboratory analyses have been summarized in three reports:

• Nitrogen concentrations in harvested plant parts - A literature overview
• Nitrogen concentrations in harvested plant parts - Update 03/2021
• Nitrogen concentrations in harvested plant parts - Update 02/2024