Compost-in-Place System

Operation Background:

ʻĀīna Hoʻokupu o Kīlauea (AHK) is a nonprofit dedicated to facilitating solutions to economic, social, and agricultural/food security challenges in the greater Kīlauea community on the North Shore of Kauaʻi. AHK was formed in order to formally steward 75 acres of Kauaʻi County land now known as the Kīlauea Community Agricultural Center.

The Kīlauea Community Agricultural Center (KCAC)’s mission is to contribute to island food security and to a healthy, stable, balanced local agricultural economy by providing valuable productive agricultural land at low or no cost to farmers, operating Kīlauea Community Farm—producing food at low or no cost to community members in need—and providing a permanent Farmers Market facility for ongoing direct-to-consumer produce market development. The market facility has been in development for the past two years.

Through the pandemic, KCAC ran a fully sponsored farmers market box program that helped to feed community members for no cost, as well as supported the farm staff and internship program. The box program continues today in partnership with the Hawaii Independent Food Bank.

KCAC’s soils are Lihue series and the area sees approximately 60 inches of annual rainfall. Soils in the Lihue series are deep, well-drained and formed from weathered igneous rock.

Yoshito L’hote leads AHK and runs the farm with his two sons. They grow row crops including leeks, carrots, arugula, radish, cucumber, beets, brassica and lettuces. They have pigs in a deep litter system as well as sheep, chickens and turkeys in their operation. Current management challenges include plant disease in particular parts of their fields, low levels of topsoil, some pest issues, and a known phosphorus deficiency. Their current practice is to use targeted applications of Boron and Phosphate fertilizers applied to the beds and at transplant, to spray with organic-approved pesticides when needed (which is rare), and to amend with pig litter and poultry litter (at appropriate application intervals according to GAP), produced on-site.

Soil Health Goals:

The farmers at KCAC are working towards some overarching soil health goals. These were developed based on recent soil health tests they had analyzed by the Crow Soil Ecology and Biogeochemistry Lab at UH Mānoa.

Soil Health Practice: On-Site Compost-in-Place System

In the Fall and Winter of 2022, the farm participated in Oahu RC&D’s Farmer Soil Health Cohort. This program, funded through a cooperative agreement with Oahu RC&D and NRCS PIA, aims to accelerate the adoption of soil health practices by farmers on Oahu, Kauai, Maui and Hawaii Island. As part of their participation in the cohort, Yoshi and his team designed and demonstrated a pilot in-field compost system. With this practice, the farmers’ goal is to build resilience to changing rainfall patterns as well as reduce reliance on imported fertilizers/nutrient sources. The composting system will help them achieve this by increasing organic matter content to build the nutrient holding capacity and aggregate structure in their soil.

Yoshi’s pilot composting-in-place system is a 120-foot compost windrow pile built up using feedstock produced in their Korean Natural Farming (KNF) inoculated pig deep litter system on site. Additional layers of feedstock used to build the piles include a 1 to 1.5 foot layer of wood chips on the bottom. To improve aeration, every 6 feet, a 6 inch diameter PVC pipe—drilled with holes—is inserted at the foundational layer and laid perpendicularly across the pile. This design aerates the piles, saving the farm labor hours as the piles will not need to be turned. Once the layers of feedstock in the pile are built to four feet in height, the pile is covered again with wood chips and left to sit until fully cured.

To ensure food safety, the farmers will carry out practices appropriate for raw manure application, keeping a log of all of their additions of litter to the pile, and will not use any of the finished compost until 120 days have passed from the last addition. The team will also keep a daily log of the pile temperature and perform microbial testing every 6 months to ensure harmful pathogens are killed through the composting process.

As a proactive measure, they are installing a vegetative barrier using vetiver to prevent nutrient leaching from the piles. By installing vetiver rows downslope from the pile, any surface water runoff will funnel into the rows and percolate along the deep root system of the plant, keeping nutrients onsite and preventing them from entering the local streams and oceans. In preparation for high rain events, Yoshi also adds an additional layer of mulch to the top of the piles to prevent surface runoff and erosion from the compost pile. This additional mitigation measure will also help reduce the loss of nitrogen through volatilization.

Weeds do tend to encroach the piles; additional mulch can be used to control weed pressure.

The KCAC team plans to have 4 or 5 rows built in the same field by the end of 2023. As of now, Yoshi and his team are still waiting for the first pile, which they started in 2022, to be ready and estimate that the compost will be fully cured and verified as safe after 12 months of building and decomposition. As this is a compost-in-place system, when the piles are mature, the plan is for them to be spread out somewhat in place, and for the farmers to roll their greenhouses over the area and plant into the composted fields. Once this happens they will begin new piles in another field.

As Yoshi gets his pig manure from his own system onsite, the only significant costs for this practice are for the PVC pipes, fuel for the skidsteer, and the labor required to move the pig waste over to the compost each day.

For the KCAC team, the labor comes out to a total of 5 to 6 hours weekly to maintain the system. This looks like one person working for 10 minutes each day to scoop out one row of pig mulch with the skidsteer and add it to the compost pile, as well as twice a week, two people taking one hour to to a more thorough cleaning of the pens and adding that pig mulch to the pile afterwards.

Monitoring and Updates:

As of March 2023, Yoshi and his team have one compost pile going strong, with plans to create up to 5 on the same field. The PVC pipes seem to be aerating the compost adequately, eliminating the need to turn the piles, though further study and microbial testing is necessary to verify the quality of the compost and the kill of any potentially harmful microorganisms.

Note: This material is based upon work supported by the U.S. Department of Agriculture, under agreement number NR2192510002C002. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the U.S. Department of Agriculture. In addition, any reference to specific brands or types of products or services does not constitute or imply an endorsement by the U.S. Department of Agriculture for those products or services.