Plant sap analysis as a diagnostic tool for winter wheat nutrient use efficiency

Progress report for OW23-386

Project Type: Professional + Producer
Funds awarded in 2023: $74,929.00
Projected End Date: 03/31/2026
Grant Recipient: Palouse Conservation District
Region: Western
State: Washington
Principal Investigator:
Ryan Boylan
Palouse Conservation District
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Project Information


In recent years, producers and conservationists alike have focused on increasing nutrient use efficiency to decrease production costs and protect the environment from the detrimental effects of fertilizer overapplication. Plant sap analysis can enable precise, real-time monitoring of nutrient deficiencies and crop health, potentially providing producers with more accurate information than traditional methods. While its use as a diagnostic tool has been explored in other agricultural systems, little information is available for the Inland Pacific Northwest (iPNW) and winter wheat specifically.

The proposed research will compare traditional nutrient management and monitoring practices with periodic plant sap analyses to guide foliar fertilizer applications on three farms. Cost-benefit analyses of the trials will quantify the economic feasibility of adding this diagnostic tool to crop fertility management.

Project results will be disseminated through education and outreach activities, including field tours, presentations at industry meetings, newsletter articles, social media posts, webpages, and informational handouts.

Study results will help producers evaluate the efficacy of adopting plant sap analysis and will have the potential to significantly advance precision agriculture thereby increasing yields while reducing costs and harmful nutrient runoff and leaching from overapplication of fertilizers.

Depending on the research findings, the project will either aid the widespread adoption of plant sap analysis through education and outreach activities or save producers time and resources by preventing unnecessary or ineffective adoption of technology. Educational resources will be used by agricultural professionals beyond the funding period.

Project Objectives:

The goals of this project are to 1) assess plant sap analysis as an effective and economical winter wheat nutrient diagnostic tool for the Inland Pacific Northwest and 2) disseminate research results and recommendations to producers. Plant sap analysis has potential to improve the accuracy of late-season foliar crop nutrient applications. If it does, plant sap analysis could help producers improve yields and crop and soil health while reducing the overall amount of fertilizer applied, thereby reducing costs and environmental impacts in contrast to fertilizer applications based on recommendations from traditional soil and tissue testing.

Three objectives will guide this project:

Objective 1: Assess the performance of winter wheat produced using fertilizer applications informed by plant sap analysis compared to the performance of winter wheat fertilized according to traditional soil and tissue testing results.

Objective 2: Evaluate producer attitudes and the economic cost-benefits of using plant sap analysis for winter wheat nutrient management.

Objective 3: Disseminate agronomic and economic cost-benefit research results through online resources, publications, and in-person events to inform adoption of sap analysis as a tool for precision nutrient management.



The proposed project will encompass three crop years beginning in April 2023 and concluding in April 2026. Major milestones will be the implementation of on-farm, side-by-side field trials to compare results of “business-as-usual” fertilizer recommendations with sap analysis. See attached project schedule for detail.

2023 WSARE Proposal - Project Schedule


Click linked name(s) to expand/collapse or show everyone's info
  • Neil Appel - Producer
  • Gerrit Bass (Researcher)
  • Ian Clark - Producer
  • Gabby Hannen
  • Kara Matson
  • Alicia Leacox - Technical Advisor
  • Elizabeth Sebo - Technical Advisor
  • Sheryl Zakarison


Materials and methods:

Objective 1: Assess the performance of winter wheat produced using fertilizer applications informed by plant sap analysis compared to the performance of winter wheat fertilized according to traditional soil and tissue testing results.

Three years of on-farm trials will be conducted on three participating Whitman County, Washington, farms. These producers use a no-tillage system and typically employ traditional methods to assess wheat nutritional needs. This has resulted in applications of fertilizer in the fall and sometimes spring to supplement natural soil nutrients.

The on-farm trials will employ a paired plot design (six plots, two on each farm) to compare 1-acre strips of winter wheat fertilized according to recommendations informed by traditional soil and plant tissue tests (control) to 1-acre strips of winter wheat fertilized in the spring according to recommendations informed by soil and plant tissue samples and plant sap analysis (treatment). Each year the strips used for soil and plant tissue test collection will be moved to a different field to follow the rotation of winter wheat. As the plots rotate with the crops, researchers will try to choose fields that are as similar as possible each year. All environmental data that could possibly add additional extraneous variables through this process will be recorded and analyzed for significance. This will include potential variables such as soil type, fertilizer applications, cropping history, slope, and aspect.

Soil samples will be collected at randomly selected locations in both control and treatment plots in the fall and spring. Soil samples will be collected and analyzed 36 times during the project (12 per year, two per control and treatment plot). Tissue tests will be collected and analyzed 18 times during the project (6 per year, one per control and treatment plot). Plant sap will be collected a minimum of three times each growing season (three per year, one per treatment plot). The varying number of samples by technique match best practices for that technique.

Plant sap is typically collected by harvesting leaves from plants in a plot. Best practices include taking two samples, one of young leaves from the top of the plant and the other of older, vital leaves from the bottom of the plant. The number of leaves required for a complete sample varies by crop and nutrients measured. PCD will work directly with lab technicians to determine the needed amount for winter wheat samples.

Soil, tissue, and sap samples will be sent to third-party laboratories for analysis. To ensure consistency throughout the project, each specific laboratory chosen for the respective analysis will be used throughout the entirety of the project. Plant sap analysis has not been standardized, and exact methodologies may vary by lab. Therefore, it is important that the same lab be used throughout the project to analyze plant sap data to ensure consistency.

Finally, PCD will collect winter wheat grain from the randomly selected locations within the six plots prior to harvest to assess quality between the control and treatments. Wheat quality includes test weight, presence of foreign material, damaged kernels, moisture, protein, gluten, grain nitrogen and falling number. PCD staff will complete nutrient use efficiency calculations for all treatments that compare the crop yield per unit of applied fertilizer. Crop yields will be compared using control and treatment strips with yield tracked using yield monitors. Yield data will be collected and reported by the participating farmers.

Objective 2: Evaluate producer attitudes and the economic cost-benefits of using plant sap analysis for winter wheat nutrient management.

Economic cost-benefit analysis will include tracking seed costs, input costs (fertilizer, pesticides, other soil amendments), labor costs, testing costs (sap, soil, and tissue), fuel costs, and other equipment costs. Costs will be subtracted from crop yield multiplied by the average price of wheat for that year. This calculation method will be used for both the control and treatment plots, and results will be compared to establish the economic viability of plant sap analysis as an alternative or addition to traditional methods.

T-tests will be used to assess the significance of differences in economic cost-benefit, yield, soil parameters, nitrogen use efficiencies, and grain quality.

PCD staff will meet with producers annually to assess project progress and collect feedback. PCD staff will also administer a questionnaire to the participating producers in the first and third years of the project to assess changes in attitude for sap testing as an additional method for spring-applied fertilizer. The questionnaire in the first year will include gathering information on recent major management activities that could affect the results of the trials. This information will help PCD determine potential extraneous variables.

Objective 3: Disseminate agronomic and economic cost-benefit research results through online resources, publications, and in-person events to inform adoption of sap analysis as a tool for precision nutrient management.

PCD will host several educational workshops and opportunities to introduce producers to plant sap analysis, share the results of our objective 1 and 2 research activities, and promote the use of proven precision nutrient management tools in the region to enable widespread adoption. If the trials demonstrate that plant sap analysis is not more cost and agronomically effective, then this information will be shared as well so that producers do not adopt ineffective techniques. Additional educational materials will be produced for online resources and publications. The educational plan outlines specific tasks associated with this objective.

Research results and discussion:

Year 1 Research Results (2023 crop year):

In the first year of the project we set up three field trials on three farms in Eastern Washington (Figure 1).  Soil samples were collected in both the 1-acre sap testing plots and the business-as-usual comparison between early April and early May. Samples were collected in three randomly selected locations in both fields. At each sampling location ten soil probes were collected in a circular pattern around the randomly selected point to 30 cm and then were composited by field.  For each plot we composited 30 soil probes and sent the samples to Regen Agricultural Labs in Nebraska.  At that point the the growing season there were only subtle differences between the two plots on all farms.  The soil sampling recommendations received from the lab helped to inform if any top dressing should be done in the business-as-usual plots and what is available for plant up take.  The recommendations from the lab indicated that most soils lacked nitrogen, phosphorus, calcium, potassium, boron, molybdenum, and zinc.  The soil sampling data can be found in Table 1 below. 

Table 1. Spring soil sampling data     

After soil samples were collected plant sap testing started.  Sap testing began in late March and continued through out the spring until early June and was sent to Apical Labs in Canby, Oregon.  The sap testing data was used to track changes in micro and macro nutrient content in old and new leaves of the growing crop and to provide recommendations for foliar applications.  As this was the first time many of the participating farmers had tested this method there was some trial and error in interpreting the results.  With recommendations from the lab and with several consultations our team was able to interpret the results.  The most common recommendations across all three sites included phosphorus, molybdenum, born, zinc, iron, and manganese. Figures 2 - 5 display the sap testing data throughout the sampling period.  Unfortunately, due to some logistical constraints one of the participating farms was unable to apply fertilizer at all in the spring.  This is one of the challenges conducting on farm trials and we have developed a plan to be successful moving forward.  The two remaining farms foliar applied fertilizer based on the recommendations received from the lab between may 15th and June 1st. 

Figures 2 - 5: Sap testing results from participating farms    

In addition to soil sampling and sap testing crop yields and gran quality were measured in both the sap testing and business-as-usual plots just before harvest.  Grain samples were only collected from two of the farms that were able to apply fertilizer in the spring.  The only significant difference that was observed between the two plots were grain yields at the APPWS farm.  The sap testing plot yielded roughly 104 bushels/acre and the business-as-usual comparison yielded 78 bushels/acre.  The ZAKWS farm showed the opposite with the sap testing plot yielding 47 bushels/acre and the business-as-usual comparison yielding 53.58.  Table 2 below has all of the yield and grain quality data collected. 

Table 2: Crop yield and grain quality for the sap and business-as-usual plots

At this point we have only been able to compile the economic data for one of the farms. We decided that we would wait until we have a full economic analysis done to submit it.  We will continue to compile the economic data for the 2023 crop year and will add it to the 2024 crop year data and submit it with our next report.  

Participation Summary
3 Producers participating in research

Research Outcomes

Recommendations for sustainable agricultural production and future research:

Year 1 Research Outcomes:

The were several outcomes from the first year of the trials that are worth noting.  First, sap testing proved to be some what logistically complicated.  The timing from when we sampled, received results and recommendations from the lab, and ordered product, and then applied the product took too long.  As was mentioned in the research results section, one of the farms was not able to foliar apply because the wheat had gotten to big and they were worried about crop damage.  With these lessons learned we have moved our sampling dates earlier in the spring and will be testing at more frequent intervals so the participating farmers will be able to look at results and order product in a timely manner.  

A second outcome that is worth discussing is that one of the participating farmers was so impressed with the sap testing plot that they decided to by a new sprayer. This individual is going to increase the acreage that they will be applying fertilizer to in the spring based on sap testing results outside of the project.  

Finally, there was a lot learned this year about the proper method, timing and interpenetration of sap testing results. For the 2024 crop year we are going to work closely with Apical labs and potentially with a crop consult to provide more accurate recommendations for our region.  

1 Grant received that built upon this project
1 New working collaborations

Education and Outreach

4 Consultations
1 Curricula, factsheets or educational tools
1 Published press articles, newsletters

Participation Summary:

Education and outreach methods and analyses:

Year 1 Education and Outreach Activities:

The first year of the education and outreach activities for the project revolved around planning and spreading the word about the project.  Through the Palouse Conservation District's social media platforms two posts were made about the project that was seen by just over 3,000 followers.  The social media posts can be seen below.  The project was also highlighted in Palouse Conservation District's Annual Report that was distributed to our mailing list reaching over 2,ooo subscribers. A copy of the annual report can be found below. We have been planning for both a sap testing stop on a field day that will be held in May 2024 and a precision agriculture field day that will take place in June 2024.  The education and outreach team have also been working with a contractor to develop our pre-project questionnaire that will be distributed prior to both of these field a days.

Sap Testing Social Media post 1

Sap Testing Social Media Post 2     

2023 Palouse Conservation District Annual Plan


Education and outreach results:

Nothing to report at this time

1 Farmers changed or adopted a practice

Education and Outreach Outcomes

Recommendations for education and outreach:

No recommendations to report at this time.

3 Producers reported gaining knowledge, attitude, skills and/or awareness as a result of the project
Non-producer stakeholders reported changes in knowledge, attitudes, skills and/or awareness as a result of project outreach
5,000 General public
Key changes:
  • Knowledge of sap testing and the logistics involved

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.