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Soil Building Strategy Using Bokashi with the Long View

The SoilFeeders farm team started out in December 2021 using Bokashi as topsoil dressing which caused disturbances in soil-plant-fauna interactions due to the volatile nutrient density of Bokashi.

Regenerating soil ecologies is a slow process and does not produce quick results. Since the regenerative application of Bokashi food waste is little researched and documented, the SoilFeeders farm team is tasked to use hotel-made Bokashi in ways that build up soil life long-term. After preliminary testing with quick soil applications of Bokashi, the farm team decided to turn the volatile food waste ferment into stable compost because it minimizes the impact on fragile soil ecologies and allows to tailor the fertilizer to the needs of crops and context.

Five months into SoilFeeders’ circular nutrient trial one could ask why SoilFeeders has not yet applied the hotel Bokashi to the soil. Instead, the collected bokashi is maturing for up to six months into stabilized compost and then will be applied to the second growing cycle of the trial. Originally, SoilFeeders’ farm team had buried larger amounts of unprocessed Bokashi into trenches of newly opened planting beds and also applied it onto the topsoil (beneath sheet mulching). However, from this experience, the team learned that it is not a sound practice for regenerating the soil. The trench application proves to be disruptive to soil ecologies and only makes sense when breaking new ground for converting pasture or a fallow field into farmland—rare occasions in a place like Hong Kong.

Working the field with the broadfork (a tool that connects a row of steel tines along a crossbar with two pole handles) to aerate the soil and mix in small quantities of Bokashi.

The SoilFeeders team has also worked Bokashi more sensibly into the surface layer using a broadfork. Here soil disturbance is minimized but only a limited amount of Bokashi can be mixed into the soil, leaving most of it still on the topsoil. As the contact surface area is much smaller, the time for breaking down the fermented food scrap is extended to 4 weeks or longer compared to trench application which takes 2 weeks. If crops are planted into Bokashi that have not fully broken down, decomposition heat is produced that ‘burns’ and thus inhibits plant roots.

Contrary to liquid or powdery fertilizer substrates, incorporating Bokashi directly into the soil requires an invasive mechanical process. For this commonly a rotary tiller (rototill) is used which agitates the top 6-12 inches of soil, causing a significant disturbance as most soil organisms are located in the top 6 inches. While rototill integrates Bokashi well into the soil thus speeding up decomposition, it also increases oxidation of organic matter and releases CO2 into the atmosphere. Moreover, beneath the rototilling blades the soil is likely to be over-compacted, a phenomenon known as hardpan. Even burying Bokashi with hand tools like a hoe causes unwanted soil agitation. While such manual methods require significant labor input they have little regenerative efficiency. Since Bokashi application is not a one-off process, the soil would be disturbed every time it is applied, about 2-3 times per year.

Hospitality professionals mix the Bokashi collected by the hotel together with the municipal mulch, and green waste into a cubic meter pile for hot-composting as an efficient way to stabilize and consolidate the fermented food wastes.

Based on the above insights, the farm team decided to convert Bokashi into stabilized organic matter through hot-composting before applying it to the soil. For compost to mature, 4-6 months are needed. Since the municipal mulch added to SoilFeeders’ compost contains a lot of hardwoods, a full 6-month maturation period is required. As Bokashi's application in regenerative farming is still without much precedence, the SoilFeeders team is developing its own approach sensitive to the local context which requires adjustments along the way.

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