A Hawaiʻi Soil Health Index to Guide Farmer Adoption of Sustainable Management Practices

Progress report for GW19-201

Project Type: Graduate Student
Funds awarded in 2019: $23,036.00
Projected End Date: 07/31/2022
Grant Recipient: University of Hawaii at Manoa
Region: Western
State: Hawaii
Graduate Student:
Major Professor:
Jamie (Jayme) Barton, M.A.
Hawaii Agriculture Research Center
Major Professor:
Dr. Susan Crow
University of Hawaii Manoa
Jonathan Deeniki
University of Hawaii at Manoa
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Project Information

Summary:

The state of Hawaiʻi enacted the Greenhouse Gas Sequestration Task Force act to begin establishing soil health criterion for a certification program where farmers and landowners may be rewarded for healthy management practices. For soil health to be accurately used as a tool, indicators must be calibrated for local conditions to establish sensitive, farmer accessible indicators, threshold values of measured indicators, and to understand soil health’s relationship to yield and carbon sequestration. Previous research identified 14 sensitive soil health indicators for Hawaiʻi, but needs to be further refined and validated to calculate soil health scores and indices, and to be relevant to farmer needs, including yield. Our research will address these shortcomings by establishing replicated on-field demonstration trials of varying management practices. We will work with farmers and facilitate farmer-to-farmer training sessions and farm tours through annual soil health workshops and a developed soil health web tool. These strategies will allow us to understand which soil health indicators are important to farmers and effectively connect soil science to farmer decision-making. Our objectives are to: (i) validate Soil Health Index for Hawaiʻi, (ii) analyze and monitor soil health for two-years to quantify management effects, and through seasons and crop cycles to identify best soil sampling time, (iii) utilize collected soil health data to initialize Soil Health Web Tool for Hawaiʻi to develop realistic management recommendations for farmers with quantified soil health benefits across the diverse land uses and soils in Hawaiʻi, and (iv) solidify farmer network in Hawaiʻi through annual soil health workshops, farmer-to-farmer training sessions, and farm tours. Our research will establish criterion for a farmer incentive program for sustainable management, use soil health to improve air and water quality, mitigate climate change, and maintain our soil resources, and empower producer decision-making through the workshops and web tool.

Project Objectives:
  1. Validate Soil Health Index for Hawaiʻi, including: (i) establishing baselines for a variety crop and soil types, (ii) measuring indicator sensitivities, (iii) calibrating index and scoring for different agricultural management practices in diverse soil types, and (iv) assessing the relationship between the index and yield.
  2. Analyze and monitor soil health for two-years (aggrading, degrading, maintaining) to quantify management effects, and through seasons and crop cycles to identify best soil sampling time.
  3. Utilize collected soil health data to initialize Soil Health Web Tool for Hawaiʻi to develop realistic management recommendations for farmers with quantified soil health benefits across the diverse land uses and soils in Hawaiʻi.
  4. Solidify farmer network in Hawaiʻi through annual soil health workshops, farmer-to-farmer training sessions, and farm tours.

Cooperators

Click linked name(s) to expand
  • Dr. Tai Maaz - Producer (Educator and Researcher)
  • Dr. Johanie Riveria-Zayas (Educator and Researcher)

Research

Materials and methods:

Project sites:

We conducted initial meetings with farmers and collaborators during September-October 2019 and February 2020. During these meetings plot locations were identified and chosen, baseline soil samples were taken, and management practices were finalized (Table 1). Unfortunately, after these initial meetings and baseline sampling, two of the producers had to terminate their experimental plots (see Challenges below). As a solution, two of the producers added a second set of experimental plots (MA`O Organic Farm and Tolentino Farm). These established plots are currently maintained. At MA`O Organic Farm the second set of plots were established on newly acquired lands that we’re unmanaged from at least 10 years. At Tolentino Farm the second set of plots were similar to the original at that site, except no compost was added to investigate the effects of reduced nitrogen rates only. 

Table 1. Soil health management strategies at each of the participating farms. 

Farm

Current practice

First strategy

Second strategy

Third strategy

MA`O Organic Farm

-Salad Mix Greens

-Then root

High inputs of local fish/bone meal by-product (“tankage”) with accumulation of excess soil P

Tankage at reduced rate

Feather meal 

Reduced feather meal

Kahumana

-Salad Mix Greens

-Then root

No fertilizer

or

Reduced rate

or

Full Tankage

Tankage + compost 

Feather meal

+ compost

Reduced feather meal + compost

Owen Kaneshiro Farm

-Pak Choi

Broadcast applications of 21-0-0 

75% Farmer Practice

Sunn Hemp + No fertilizer

Sunn Hemp + 50% FP

Tolentino Farm

-Eggplant

Extremely high rate of fertigated urea, 50% N added as current practice

Reduced rate of fertigated N (25% of farmer practice)

Fertigated N fertilizer

+ compost

Reduced rate of fertigated N

+ compost

Twin Bridges Farm (first year)

-Asparagus

Blended NPK fertilizer

100% Blended NK and no P  + compost

Fertigated fertilizer and no P  + compost

Reduced rate of fertigated and no P  + compost

Twin Bridges Farm (first year)

-Corn

Farmer practice

Compost 20 T/acre + 100% N no P

Compost 20 T/acre + 75% N no P

Compost 20 T/acre + 50%N no P

Aloun Farms

Terminated

Terminated

Terminated

Terminated

Counter Culture

Terminated

Terminated

Terminated

Terminated

Soil health sampling and testing:

The soil health baseline samples were taken from each plot prior to the implementation of treatments. We sampled soil from 0-15 centimeters. Three subsamples from the same vicinity were homogenized to comprise one soil sample. Within each plot, three separate samples were taken from across the plot (i.e., the plot was visibly separated into thirds). Before soil samples were taken, the organic debris on the soil surface was carefully removed. Unfortunately due to COVID-19 regulations and farmer’s decided COVID-19 precautions, sampling in year one (after baseline) did not occur at any farm and year two sampling has only occurred to date at Twin Bridge in November 2020 and Kahumana in December 2020. After sampling, the soils were immediately frozen until lab processing began.

Proposed soil health indicators for Hawaiʻi in Table 2 are being measured following protocols in Hubanks 2019. Due to university fiscal procedures we could not access grant funds until the end of December 2019, so lab processing could not begin until January 2020 (see Challenges below). Then due to COVID-19 and scheduled building construction (see Challenges below), the labs were closed from March 2020 until August 2020. Upon reopening, lab analyses were further delayed as we moved backed into our lab spaces and set up our needed lab equipment. Percent organic carbon, COburst, pH, and water holding capacity were measured for the baseline soil samples at the five farms that continued participating in the research.

Percent organic carbon

We subsampled each soil sample and it was oven-dried at 105°C for at least 48 hours. After the soil was oven-dried, the sample was ground to pass through a 250 μm sieve. Then the samples were acidified by fumigating it in an airtight container of hydrochloric acid. Lastly, approximately 0.25 mg of soil was weighed into combustion tins and were measured using an elemental analyzer. 

COburst

Soil samples were air-dried for at least 7 days. Then approximately 25 g of soil was transferred until a 610 ml airtight container with a septum on the lid. The soils were rewetted to 60% water holding capacity and the containers were sealed and placed in a 25°C incubation chamber for 24 hours. The headspace gas in the containers was sampled and measured for carbon dioxide concentration using gas chromatography. 

pH

Soil samples were air-dried for at least 7 days. Then approximately 10 g of soil was mixed with 20 ml distilled water (1:2 ratio of soil:water). The solution sat for 30 mininutes, and then the pH was measured using a pH meter.

Water holding capacity

Soil samples were air-dried for at least 7 days. Then approximately 10 g of soil was added to a bottomless 50 ml centrifuge tube that had an attached Whatman #52 filter on the bottom. The centrifuge tubes were lowered into a pan of water — rewetting the soil to saturation via capillary action. Once the soils were saturated, the tubes were removed from the pan of water and drained for one hour. After draining, the soils were reweighed to calculate the volume of water retained.

Table 2. Proposed soil health indicators for Hawaiʻi

 

Challenges:

  1. Grant funds were not available until December 20th, 2019 due to university fiscal processes. Because of this delay, soil health baseline lab analyses could not begin until January 4th, 2020. 
  2. COVID-19 unexpectedly and completely changed the way the world works, and we were no exception. Hawai’i ordered an initial stay-at-home order in March 2020. Though our work is essential, it took time for us to adapt to altered working conditions — moving our offices into our homes, organizing meetings online, limiting the people in lab at one time, and adjusting our lives for the new normal. This reduced our possible productivity, particularly during the beginning of shutdown orders. While we have improved on this difference in actual vs. expected productivity, the continuing pandemic still affects our available in-person work hours in order to ensure the continued safety of our lab group. Additionally, due to the exacerbated strains from the pandemic, including lease agreements and the decrease in agritourism, Counter Culture and Aloun Farms had to discontinue their participation in this research. 
  3. In addition to COVID-19 limiting the total working hours that we could spend in the lab for sample processing, our labs were shut down completely from May to August for necessary building maintenance. This building project necessitated evacuation of our equipment, lab supplies, and soil samples from lab spaces within the building — completely halting lab work until its completion. We are still in the process of re-moving into our lab spaces, and re-calibrating and tuning all equipment. 
Research results and discussion:

At the preliminary stages – before soil health scoring calibrations – we can only roughly interpret soil health indicator results (Table 3). All farms are on soil orders that have high activity clays (Mollisols and Vertisols), thus are generally expected to have relatively high fertility and soil health. However, because of this, many of these soils are degraded in Hawaiʻi due to overuse in monocultures over the last 100 years. 

Below are the results for percent organic carbon (Table 4), COburst (Table 5), pH (Table 6), and water holding capacity (Table 7) from the baseline soil sampling for the original five farms planned. We will compare these results to year two soil sampling to learn if the treatments at each farm maintained, increased, or decreased soil health. Additionally, year two sampling includes soil sampling through crop cycles to determine if soil health is affected by sampling time. Lastly, we will conduct a post-hoc power analysis to assess the sensitivity of the soil health indicators.

Table 3. Hawaiʻi soil health indicators and their function and interpretation.

Table 4. Organic carbon (%) in the baseline soil samples from the on-field demonstration trials at each farm prior to the soil health management strategies implementation. The first number is the average of the three samples taken from each plot and the second number is the standard error.

Farm Soil Order Current practice First strategy Second strategy Third strategy
MA`O Organic Farm Vertisol 1.36 ± 0.18 0.85 ± 0.06 1.36 ± 0.09 1.52 ± 0.08
Kahumana Vertisol 1.38 ± 0.09 1.26 ± 0.03 1.14 ± 0.05 0.99 ± 0.12
Owen Kaneshiro Farm Mollisol 1.50 ± 0.02 1.36 ± 0.01  1.26 ± 0.05 1.38 ± 0.03
Tolentino Farm Vertisol 1.93 ± 0.13 1.50 ± 0.07 1.50 ± 0.01 1.34 ± 0.00
Twin Bridges (asparagus) Mollisol 2.18 ± 0.02 1.97 ± 0.15 2.26 ± 0.08 2.50 ± 0.07
Twin Bridges (corn) Mollisol 1.49 ± 0.04 1.54 ± 0.01 1.69 ± 0.11 1.40 ± 0.06

Table 5. COburst (μg of C/g of soil) in the baseline soil samples from the on-field demonstration trials at each farm prior to the soil health management strategies implementation.  The first number is the average of the three samples taken from each plot and the second number is the standard error.

Farm Soil Order Current practice First strategy Second strategy Third strategy
MA`O Organic Farm Vertisol 36.41 ± 14.77 41.57 ± 17.07 13.24 ± 1.63 24.41 ± 0.35
Kahumana Vertisol 64.74 ± 3.30 65.81 ± 7.75 65.31 ± 6.78 55.76 ± 7.24
Owen Kaneshiro Farm Mollisol 17.16 ± 1.38 17.18 ± 0.55 12.53 ± 1.05 8.93 ± 0.88
Tolentino Farm Vertisol 50.56 ± 1.45 44.66 ± 4.13 28.35 ± 1.91 26.15 ± 3.42
Twin Bridges (asparagus) Mollisol 29.07 ± 0.96 30.62 ±  0.49 33.88 ± 0.23 29.94 ± 1.68
Twin Bridges (corn) Mollisol 14.29 ± 2.04 11.60 ± 0.84 6.23 ± 6.31 13.06 ± 0.40

Table 6. pH in the baseline soil samples from the on-field demonstration trials at each farm prior to the soil health management strategies implementation. The first number is the average of the three samples taken from each plot and the second number is the standard error.

Farm Soil Order Current practice First strategy Second strategy Third strategy
MA`O Organic Farm Vertisol 7.46 ± 0.25 7.49 ± 0.16 7.76 ± 0.20 7.72 ± 0.27
Kahumana Vertisol 7.82 ± 0.09 7.68 ± 0.06 7.63 ± 0.12 7.82 ± 0.19
Owen Kaneshiro Farm Mollisol 8.20 ± 0.03 8.38 ± 0.12 8.33 ± 0.05 8.65 ± 0.05
Tolentino Farm Vertisol 7.52 ± 0.12 7.45 ± 0.05 6.67 ± 0.11 6.39 ± 0.14
Twin Bridges (asparagus) Mollisol 6.45 ± 0.07 6.57 ± 0.11 6.42 ± 0.04 6.44 ± 0.05
Twin Bridges (corn) Mollisol 8.57 ± 0.02 8.58 ± 0.02  8.59 ± 0.05 8.57 ± 0.02

Table 7. Water holding capacity (%) in the baseline soil samples from the on-field demonstration trials at each farm prior to the soil health management strategies implementation. The first number is the average of the three samples taken from each plot and the second number is the standard error.

Farm Soil Order Current practice First strategy Second strategy Third strategy
MA`O Organic Farm Vertisol 79.14 ± 2.75 77.44 ± 4.78 73.79 ± 3.54 72.51 ± 3.30
Kahumana Vertisol 96.86 ± 3.45 100.55 ± 6.62 91.86 ± 4.31 90.48 ± 2.08
Owen Kaneshiro Farm Mollisol 82.60 ± 4.49 92.22 ± 2.39 93.74 ± 4.90 82.17 ± 1.31
Tolentino Farm Vertisol 89.71 ± 4.17 91.14 ± 3.59 89.21 ± 1.86 89.94 ± 2.00
Twin Bridges (asparagus) Mollisol 74.40 ± 2.52 81.07 ± 3.18 78.55 ± 1.53 84.19 ± 1.68
Twin Bridges (corn) Mollisol 63.34 ± 1.97 63.61 ± 4.03 61.92 ±1.57 61.12 ±1.06

Timeline

Participation Summary
7 Farmers participating in research

Educational & Outreach Activities

7 Consultations
3 Curricula, factsheets or educational tools
5 On-farm demonstrations
1 Online trainings
2 Webinars / talks / presentations

Participation Summary

5 Farmers
17 Ag professionals participated
Education/outreach description:

By leveraging this project and other soil health efforts we created a Hawai`i ​Soil Health website where we publish news, blogs, outreach activities, and links to our Hawai`i ​Soil Health Tool. The Hawai`i ​Soil Health Tool allows producers to track their soil health through time. They are able to plot their fields on a map and interactively interface with their soil health results. 

In August 2020, we started our soil health webinar series. For the first of the series we invited all College of Tropical Agriculture and Human Resources (CTAHR) extension agents and specialists for a two-part webinar — soil health basics for Hawaiʻi and Hawaiʻi Soil Health web tool tutorial. The first week we presented the basics and background of soil health and testing in Hawaiʻi and used local results from these demonstration trials and other activities. The second week we demonstrated the Hawaiʻi Soil Health Tool and guided extension agents and specialists through a tutorial of using the tool. Videos of these recordings are posted on the Hawaiʻi Soil Health website for viewing at any time. Because many of our relationships to producers and land owners are through extension agents and specialists we began with their training to help during future webinars with producers and with recruiting new producers and land owners to attend.

In progress: 

Once we have year two soil health results, we will have one-on-one meetings with our participating producers in collaboration with partnered extension agents to demonstrate the Hawaiʻi Soil Health Tool and guide them through using the tool themselves. Their feedback will be incorporated into the next tool updates. After we conduct these meetings, we will continue the webinar series by land use (e.g., cropland). From our producers participating in this project, we will identify those farmers that would like to share their experiences and new knowledge gained during the project to present or pre-record a video to share during these webinars.

Challenges: 

Originally we planned to have more comprehensive workshops with tours that facilitated on-hands farmer-to-farmer training. Obviously, we were unable to schedule such workshops due to COVID-19 this year, but are planning to organize them once it becomes safe to do so. Additionally, as there is often a technology barrier, virtual meetings add to the difficulties in communication and training, particularly when other concerns may be occupying producers’ time. 

Project Outcomes

5 Farmers changed or adopted a practice
2 Grants received that built upon this project
Did this project contribute to a larger project?:
Yes
3 New working collaborations
Project outcomes:

While COVID-19 has hindered our capabilities to sample and process those samples as we had originally planned, it has not hindered the development of our Hawaiʻi Soil Health Tool. At this time, the Hawaiʻi Soil Health Tool has all functions that will compose the finalized tool. We have consistently tested these functions, both internally and with College of Tropical Agriculture and Human Resources extension agents and specialists, and are refining them based on feedback from these tests and to increase ease of use. Within the next year, we aim to begin testing the tool with producers directly. We have received an excellent response to the tool and expect it will greatly assist the decision-making producers face when managing a farm, and will help improve soil health and ultimately the productivity of producers’ fields.

Our initial webinar about soil health and the Hawaiʻi Soil Health Tool helped extension agents understand our plans and will lead to recruitment of producers interested in furthering their goals in sustainability while maintaining or increasing their productivity. We plan to continue to expand our outreach to producers and their communities in order to spread more awareness and care for an agricultural systems build on long-term sustainability.

Knowledge Gained:

Certainly, this year we learned that unpredictable situations can alter the course of producers’ plans, no matter how sound. COVID-19 greatly altered the plans of both producers and our research. Two producers had to drop out due to lease agreements and decline of agritourism this year due to the decline in demand. We have learned that we need robust strategies, systems, and tools that can be adapted to changes as close to in real time as is feasible in order to maintain soil quality and sustainable systems.

We learned that complex farm management practices including multiple crop cycling along with demonstration plots and others require equally complex strategies. Sustainable practices will change not just between farms and crops, but will change from plot to plot and depend on what stage of a cycle the crops are on. Sustainable strategies and tools need to be able to account for these cycling management practices in order to prove valuable for producers and maintain soil health.

Sustainable agriculture is necessary but difficult in year-round tropical systems, where the soils are often producing for numerous cropping cycles and temporarily bare in between plantings. Namely, we learned cover crops in year-round systems greatly increase the need for management in order to maintain the health of the soil. For example, cover crops require water needed elsewhere for currently growing crops, or require additional expense that producers may wish to avoid. Our management suggestions for optimizing soil health will need to take these factors into consideration.

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.