Estimating the Application Rate of Locally Produced Liquid Organic Fertilizer to Meet Crop N Requirement

Progress report for OW23-378

Project Type: Professional + Producer
Funds awarded in 2023: $74,547.00
Projected End Date: 08/31/2026
Grant Recipient: University of Hawaii at Manoa
Region: Western
State: Hawaii
Principal Investigator:
Dr. Amjad Ahmad
University of Hawaii at Manoa
Joshua Silva
University of Hawaii at Manoa, College of Tropical Agriculture a
Jensen Uyeda
University of Hawaii
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Project Information


Replacing imported fertilizers with local resources is among the highest research and educational priority identified by stakeholders statewide. The need for N solution fertilizer derived from local resources has been fulfilled through a previous Western SARE award (SW14-026) and meant to be as a supplemental application. The recipe became very popular, especially among organic growers, and they call it “Tankage tea”. The growers currently are using the recipe as a main source of N for annual crops and fruit trees. However, there is a need to determine if the recipe is meeting crop N requirements for optimum yields or if excessive application is causing environmental pollution. The proposal aims to estimate N application rate using a new bio-mineralization filtering system which allows for a 1-week extraction period, instead of the old filtering system limited to only a 1-day extraction period. On-farm trials will be conducted using various crops. Solution and soil samples will be analyzed to determine nitrate, ammonium, and total N. This will allow us to calculate 1) N application over a crop growth period, 2) crop yield, and 3) soil fertility changes over 2-years period. On-farm field days and workshops will be conducted statewide to disseminate the project findings. Video demonstration of the system setup and extension bulletins with project results will be published online. This project is expected to benefit grower’s profitability and local food production sustainability, by providing the crops with required N, reducing nutrient losses, and improving soil health and fertility status.

Project Objectives:
Objective 1) Estimating nitrogen application rate/load using locally made liquid organic fertilizer in on-farm trials.
Objective 2) Measure crop growth and yield response to the use of liquid organic fertilizer as sole nitrogen source.
Objective 3) Develop recommendations, video demonstrations, and educational materials for distribution statewide.
 Objective 4) Conduct field days and workshops to disseminate the project findings and increase adoption rate.

Objective 1): From May 2023 to April 2025.

Conduct field trials on collaborators farms, nutrient solution extraction and collect/analyze solution (Activity 1) and soil samples (Activity 2), and soil health (Activity 3) data to develop nitrogen application and soil health recommendations based on the collected data.


Objective 2) From August 2023 to July 2025.

Collect yield data (Activity 1) and Relative Chlorophyll Content (Activity 2) and plant samples (Activity 3) from both annual and perennial crops tested on the collaborators farms and compare that to recorded optimum yield/nutrient content from each crop to ensure that the crops are getting the required nitrogen for each crop. Develop recommendations based on the data collected.


Objective 3): From May 2024 to April 2026.

Peer-reviewed articles (Activity 1), video demonstration (Activity 2), and extension bulletins/recommendations (Activity 3) using the data collected from Objective 1 and 2 will be used to develop the outreach/education materials.


Objective 4): From August 2024 to April 2026.

Field days/Workshops in year 2 and 3 of the project duration (Activity 1) statewide on 4 (Big Island, Kauai, Maui, and Molokai) major islands (beside Oahu) to demonstrate the new extraction system and increase awareness of the project results statewide. On collaborator farms in year 2 of the project (Activity 2) field days/workshops will be conducted to increase adoption through farmer-to-farmer transfer and knowledge sharing. Public presentations (Activity 3) will be given statewide to disseminate the project findings about the new extraction system, soil fertility, crop yield, and soil health benefits from it.


Click linked name(s) to expand/collapse or show everyone's info
  • Ramsey Brown - Producer
  • Daniel Carroll - Producer
  • Mark Hamamoto - Producer
  • Taylor Kellerman - Producer
  • Seneca Klassen - Producer
  • Gary Maunakea-Forth - Producer
  • Gabriel Sachter-Smith - Producer
  • Gavin Shon - Producer
  • Jon Watase - Producer
  • Christian Zuckerman - Producer


Materials and methods:

To reach the expected outcomes, 4 objectives (2 for research and 2 for educational purposes) were developed.

Objective 1) Estimating nitrogen application rate using locally made liquid organic fertilizer in on-farm trials.

Due to high cost of inter-island travel, the project team will be conducting the on-farm trials on Oahu Island only and will disseminate the project findings through demonstration field days/workshops on the other islands in years 2 and 3 of the project duration.

On-farm trials (on all 10 collaborator farmers-Please see collaborator letters) will be conducted using the new extraction system (350-gallon tote, air pump, bio-mineralization filtering system, injector and drip irrigation lines) for various annual crops and fruit trees (expected crops to be tested are: Sweet corn, Sweet potato, Onion, Taro, Papaya, Avocado, Banana, Breadfruit, cacao, and leafy green). Since Tankage tea is primarily a N source, initial soil test from each of the collaborator farms will be analyzed for total nutrient content and additional fertilizer (P, K and other nutrient) will be added based on each soil results to mitigate any potential nutrient deficiencies aside from Tankage applications. Each trial will be conducted with at least 3 replicates to ensure highest data quality. The extraction will be conducted using the same recipe developed through the previous WSARE award ( However, due to the new filtering system, the extraction will be 3 extractions in one week and once a month (e.g. Monday, Wednesday, and Friday of the first week of each month). This application schedule is decided based on a virtual meeting with the collaborator farmers. The decision was made for the following reasons: 1) Higher extraction of N from same solid fertilizer mix if it’s 3 times continuous extraction, 2) it’s expected to meet the crop requirements compared to previous recipe, and 3) to measure energy/electricity cost from such extraction compare to yield benefits. The solution will be prepared for ~250 gallon to ensure enough space for solid fertilizer, tubing, and oxygen dissolving stones. Also, adjustments maybe made after the 1st growing season, if amount or concentration are found to cause less than optimum crop yield or excessive nutrient application). The activities in each field trial will be:

  1. Prior to each application, 3 solution samples will be collected from the extracts and stored in a cooler with ice (to reduce the chance of nutrient forms changes), then submitted for Nitrate (NO3-N), Ammonium (NH4-N) and total N content (preliminary results showed a negligible NH4-N concentration compared to NO3-N and total N. During the 1st growing season, If NH4-N continues to be negligible, we may stop testing for it and use the fund to purchase more supplies for the collaborator farmers).
  2. Random 3 soil samples, from the application plot, will be collected a day after the extract application and samples will be analyzed for NO3-N, NH4-N and total N content (similarly to Activity-1, when it comes to NH4-N in soil).
  3. At the beginning and end of each trial, random soil samples will be collected to measure changes in soil fertility and the same soil samples collected at the beginning and end of each trial will be tested for biological activities using Solvita soil health kit (Soil Test - Solvita Field Soil Test - for measuring soil CO2 respiration). The data will be used to calculate cumulative N application over each growing season (annual for fruit trees) and compare them to crop requirement. Reflectoquant (Reflectoquant® test strips ( strips will be used to measure real time solution and soil NO3-N concentration (previous studies found a correlation of R2 = 0.96 between chemical analysis and Reflectoquent strips reading of NO3-N content in soil solution) and will be compared with chemical analysis results (If similar results will be obtained during the 1st growing season, we may cut down on NO3-N chemical analysis and use the fund to purchase more supplies to each collaborator farmer).


Objective 2) Measure crop growth and yield response to the use of liquid organic fertilizer as sole nutrient source.

At each of the field trials in Objective 1, crop growth and yield will be measured by:

  1. At the end of each growing season (harvest time for fruit trees) small areas of each plot (to reduce impact on the collaborator-farmers) will be collected for yield data (collaborator-farmers will be asked to provide full yield numbers from each plot as well).
  2. Each month, after the complete 3 extract application, Minolta-SPAD chlorophyll meter will be used to measure relative chlorophyll content (RCC) in crop leaves (RCC is highly correlated with N level in soil). The leaf RCC data will be plotted against NO3-N, NH4-N and total N, in both solution and soil samples, to find the best nutrient level for optimum crop yield.
  3. At harvest, random plant samples will be collected and analyzed for N content in the tissue. This data will be compared with optimum recorded N level in each crop to ensure that the crops are getting the required level.
Research results and discussion:

The new extraction system have been assembled and tested for the nitrate and ammonium concentration in comparison to the old extraction recipe. 

Higher nitrogen (nitrate and ammonium) extraction rate have been reached using the new extraction system. ~300% increase in the nitrate content in the extraction system is achieved (previous recipe reached 50ppm, the new extraction system achieved 150ppm). 

Due to higher extraction rate, the project team is testing extracting from same batch of solid fertilizer or the use of new batch of solid fertilizer for each application (The project team believes that will make a great financial impact on the farmers and reduce waste). 

The higher extraction rate allowed for reaching crop nitrogen requirements in less number of applications. This will have a financial impact on the growers by reduce the need for labor. 

Soil and extraction solutions have been collected and analyzed for nitrogen content to use after crop harvest in data analysis, developing recommendations, and other outreach activities. 

The project team is testing the extraction system using solar-panels for off-grid farms. This will have great benefits for the local growers by reducing transportation of 250+ gallon of extract solution from extraction place to application place (if the farm is off-grid). 

Two on-farm trials running currently to minimize the need for adjustments on all on-farm trials until the final setup is complete and all collaborator farmers receive the final extraction system. 

Participation Summary
12 Producers participating in research

Research Outcomes

Recommendations for sustainable agricultural production and future research:
  1. The new extraction system have tripled the nitrate concentration in the extraction solution. Previous extraction recipe reached 50 ppm nitrate. The new extraction system reached 150 ppm nitrate with 300% increase. 
  2. The new extraction system is using the same old recipe with an addition of bio-mineralization attachment that allowed for higher/faster extraction of nitrogen from the solid fertilizer into the aqueous solution. 
  3. The higher mineralization rate have allowed for fulfilling the crop nitrogen requirements with less number of extraction applications. 
1 New working collaborations

Education and Outreach

3 Consultations
1 On-farm demonstrations

Participation Summary:

Education and outreach methods and analyses:

Objective 3) Develop recommendations, video demonstrations, and educational materials for distribution statewide.
1. Peer reviewed articles will be published in venues appropriate to the target audience, e.g. Agroecology, Sustainable Systems, and HortTechnology.

2. A previously developed video demonstration for the preparation of the liquid organic fertilizer, will be updated using the new bio-mineralization filtering system and application recommendations based on the solution, soil samples, and crop yield collected in Objective 1 & 2.
3. At least 3 extension bulletins will be developed from this project, including, stepby-step DIY demonstration of the new extraction system, crop growth and yield in response to the extract application, and soil fertility and health data.

Objective 4) Conduct field days and workshops to disseminate the project findings and increase adoption rate.
1. Four (4) extraction systems (2 in year 2 and 3) will be purchased for the 4 islands (Big Island, Maui, Kauai, and Molokai) to be used during the workshops/field days. Afterwards, the extraction systems will be donated to GoFarm chapters on each island to be as an educational tool and used by the new cohorts in their plots. On-farm trials on Oahu will be at some of the collaborators-farms and demonstrations of the new extraction system will be conducted in year 2 and 3 of the project duration.
Public presentations will be given on each island to disseminate the project findings in relation to the new extraction system benefits, nutrient extraction level, crop growth and yield responses, and soil fertility and health benefits.

Education and outreach results:

During a farm visit by the project team and talking about the improved extraction system, a new collaborator farmer asked to be included in the on-farm trials. 

Education and Outreach Outcomes

Recommendations for education and outreach:

Nothing to report at this stage (except an on-farm visits for farmers using old extraction system and planning to adopt the new extraction system).

Workshops/on-farm field days will be conducted after harvesting crops from the current on-farm trials results.

Outreach events will be conducted for the new extraction system setup/benefits and crops growth/yield responses. 

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.