Using Biochar to Increase Soil Health and Microbiology

Operation Background:

Thrive Hawaii Family Farm is a 2.5-acre certified organic operation in Haleiwa. Both GoFarm Hawaii graduates, Jennifer and Jason Witte lease the land and grow productive food crops like cassava, bok choy, spinach, eggplant, zucchini and other mixed greens and root vegetables. They sell CSA shares locally as well as operate Farm to Barn Cafe on the property, selling breakfast and lunch made with farm produce.

Since beginning their operation, Jennifer and Jason have prioritized rehabilitating their fallow farmland back to health. Soil health practices they have incorporated include soil carbon amendments (compost, biochar, and green mulch), installing windbreaks, rotating crops, and managing irrigation. These practices restore function and health to their soil, and regular soil testing guides their nutrient application.

On a regular basis, Jenn and Jason’s fertilizer program includes prepping all beds with bone meal (tankage) or azomite (volcanic ash). They do another heavy fertilizer application just before planting. They also use a backpack sprayer to apply large batches of kelp extract for nitrogen and KNF sulfur, and occasionally fish emulsion.

Jason and Jenn apply compost every three to six months, which they source from Island Topsoil. They use 2 wheelbarrows full of compost per 100 foot bed. The farmers are happy with the quality of Island Topsoil’s product, which is created following OMRI standards for balanced composting.

For pests, Jenn and Jason spray neem and soap surfactant, and use black plastic to control weeds as needed.

Soil Health Practice:

Through their participation in the Soil Health Cohort Training Program Oahu RC&D launched in partnership with NRCS in March 2022, Thrive Hawai’i Family Farm conducted a trial to integrate biochar into their farm management system to further enhance their soil microbial habitat, continue increasing soil carbon, and potentially enhance water holding capacity.

The trial was designed to integrate biochar application as closely as possible into Thrive’s existing operation and its practices.

Three one hundred foot beds were divided up into four sections each, and different combinations of fertilizer (the growers’ existing practice of tankage and azomite), compost, and biochar were implemented (see trial design below).

Amendments were worked in with a BCS harrow and had access to 6 in drip irrigation as needed.

Monitoring and Updates:

Unfortunately, due to unexpected crop issues clear data was not able to be collected from this trial. A second crop trial within a greenhouse was also tried with zucchini, but unfortunately no substantial results were observed.

One important consideration for any farmer applying biochar is that it can take time to improve soil properties and nutrient availability for plants. One application of biochar can last for up to a decade as biochar does not decompose easily (source). Too high applications of biochar may also lead to decline in crop yield due to its large surface area, which allows the nutrients to attach to it and makes them unavailable for plant uptake.

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.