Assessment of Harvested and Sequestered Nitrogen Content to Improve Nitrogen Management in Crops

Assessment of Harvested and Sequestered Nitrogen Content to Improve Nitrogen Management in Crops (Harvested and Sequestered Nitrogen Assessment) is a project initiated by the Southern San Joaquin Valley (SSJV) Management Practices Evaluation Program (MPEP) Committee to provide growers and water quality coalitions with reliable data about nitrogen (N) removed from fields in harvested biomass, and N sequestered in perennial crop tissues (such as roots and wood). Growers can then use this information to make more informed decisions regarding nutrient management practices and crop demand; and regulatory metrics calculated by coalitions, and based on N removal, will become more accurate. More effective nutrient management planning will help to minimize the quantity of N lost to leaching below the root zone while maintaining crop yields. Data from this study will provide updates to the 2016 report Nitrogen Concentrations in Harvested Plant Parts – A Literature Overview (N Concentrations Report) (Geisseler, 2016).


Dr. Daniel Geisseler, Assistant Professor, Nutrient Management CE Specialist, University of California, Davis
Numerous other industry and UC cooperators, while not named as such in funding proposals, helped to develop the project, and will be involved in the work, or will support it with results from other projects that they are completing.

Budget and Funding

The overall budget for this project is $284,000 over three years. The MPEP Committee was awarded a grant for $224,095 from the California Department of Food and Agriculture Fertilizer Research and Education Program grant program in 2017. Additional funding comes from the MPEP Committee, from a Conservation Innovation Grant to the Committee by the United States Department of Agriculture’s Natural Resources Conservation Service, and from in-kind contributions from project collaborators.


In the 2016 N Concentrations Report, Dr. Geisseler developed factors to convert the yields of 72 major crops in the Central Valley into N removed from the field. The resulting coefficients were based on the best available information in scientific literature, with the understanding that further refinement would take place later. Due to the age and location of the studies referenced, the final N Concentrations Report (Geisseler, 2016), showed that only 10 crops, covering approximately 12 percent of irrigated lands in the Central Valley, had a solid underpinning for N content in harvested material. Furthermore, even fewer data were available on the amount of N sequestered in perennial crop biomass.

Upon further discussion with commodity groups and experts knowledgeable about each crop during development of this project, it was determined that for some crops there is a severe lack of N-removed data, while for others, the data exist or are being developed as part of ongoing studies or projects. Three categories of opportunities for developing data to inform Y-to-R and N sequestration coefficients are presented in Table 1.

Table 1. Opportunities to refine coefficients, based on discussions with researchers, commodity representatives, and grower/packer/shippers.

To refine the remaining coefficients, this project will assess harvested N content in priority crops (prioritization based on the N-concentrations Report, input from other experts, and availability of collaborators). These new data will supplement existing datasets with additional recent, local, samples from fields across the Central Valley over three growing seasons. These values will also be established for sequestered N in the standing biomass of perennial crops. With these results, growers’ N planning will be better informed, and growers, coalitions, and the Water Boards may more accurately assess progress in the reduction of leachable N in agricultural systems across the Central Valley.


Project objectives are the following:

  1. Assess N concentration of harvested material removed from fields (N mass removed [R]/Harvested material mass [Y]) for approximately 22 crops over several growing seasons.
  2. Establish values for the annual amount of N sequestered in standing biomass for seven perennial crops.
  3. Refine crop yield (Y)-to-R conversion factors, and add N-sequestration rate estimates, for use by growers and grower advisors during nutrient management planning and by coalitions for landscape-scale performance assessment.
  4. Promote and enable expanded knowledge and appropriate use of N-removal coefficients and N-sequestration rates (as part of routine N-management planning and evaluation) by growers, grower advisors, and coalitions. This includes the following:
    a.  Incorporate this information into updates to the N-concentrations Report, and develop an expanded discussion of the appropriate use and applicability of N-removal and N-sequestration estimates in formulating more precise N-fertilizer recommendations.
    b. Update existing online and off-line tools that facilitate estimation of N-fertilizer management in single fields, or in groups of fields, as well as regional assessment of N balance in irrigated croplands.


To refine the remaining coefficients, we will assess harvested and sequestered N concentration in 22 crops (see Table 1) with data collected through one of the following three methods (depending on the crop and data availability). This approach was developed for these commodities through extensive discussions with commodity groups, scientists, and producers.

a.  Incorporate existing, available data (three crops for both N removed and N sequestered);

b.  Incorporate new data from sampling and analysis efforts currently in progress and separately funded (13 crops for N removed; N sequestered for four of these)

c. Obtain new data through targeted, new sampling and analysis in collaboration with partner scientists and grower/packer/shippers; (six crops for N removed, and N sequestered for one of those six).

Newly planned and funded sampling under this Project (Item C above) would span several seasons to account for variation due to differences in weather conditions that affect yields and N-use efficiency. Specific sampling protocols and analysis methods will be defined in detail for each crop to account for variability among cultivars, harvest dates, individual fields, and years of harvest. We will coordinate with scientists, and grower/packer/shippers to procure samples for analysis, and manage, summarize, and interpret results to inform updates to the N-concentrations Report. Analyses will include quality control involving use of “blind” duplicate samples to estimate reproducibility of sample and processing methods and lab measurements.

Results will be incorporated into updates of the N-concentrations Report under this Project. The existing Y-to-R calculator ( ) will be revised to reflect the Project’s findings, and the results will be used to update the assessment and planning tools available to growers, grower advisors, coalitions, and regulators.

Tasks and Schedule

Work is organized into the following, generally sequential, tasks as indicated by the completion year following each task:

  1. In 2017, pilot sampling of peaches, in collaboration with grower/packer/shipper Gerawan Farms (Reedly, CA), is ongoing. The main objective is to refine sampling and analysis methods, and to identify the role of fruit size and seasonality (from early to late-late harvest varieties) in determining rates of N removal per pound of harvested fruit.
    Establish sampling protocols and analysis methods (2018), acquire data from others (2018-2020).

    1. Sample and assess harvested and sequestered N concentration (2018, 2019, 2020)
    2. Interpret results, and develop and publish annual updates to the N-concentrations Report (2018, 2019, 2020)
    3. Develop and publish Y-to-R calculator updates (2018, 2019, 2020)
    4. Outreach to growers and grower advisors (2019, 2020)


For more Information

For more information about the Harvested and Sequestered Nitrogen Assessment Project, contact the project leaders:

Ms. Charlotte Gallock
Coordinator, SSJV MPEP Committee
Kings River Water Quality Coalition

Dr. John Dickey
Technical Program Manager

Dr. Ken Cassman
Senior Agronomic & Soils Advisor