Evaluation of bokashi fermentation leachate as a biofertilizer in urban horticulture : inorganic plant nutrient content in bokashi leachate and its effect as a fertilizer on pak choi

Abstract: The leachate obtained from bokashi fermentation household vessels, are among proponents of the bokashi method believed to be useful as a biofertilizer. The bokashi fermentation method does not lead to foul odours as it is anaerobically fermented in air-­tight bins with lactic acid bacteria, among other groups of microorganisms, and is therefore interesting in the light of an increasing interest of urban farming and unexploited resources of plant mineral nutrients within the urban area. To examine the potential use of bokashi fermentation leachate as a biofertilizer in an urban farming context, leachate obtained from fermentation of food waste from four different sources in Malmö and Lund, Sweden, was tested on pak choi. The leachate was tested in a sand substrate, a garden waste compost substrate and a peat substrate, in order to give a general idea on how the leachate could be applied in actual situations in urban farming projects, with varying use and availability of substrates and soil. The plant mineral content of the leachates varied depending on food source, although the leachates were generally low in nitrogen, supposedly as a result of denitrification during the fermentation process. Thus, substrates low in nitrogen gave poor growth for all leachate treatments, although significant difference between different leachate treatments, were found in all substrates. All leachates were relatively high in potassium and phosphorous. The plants were fertilized with two concentrations of leachates diluted in water. Treatments with higher concentration of leachate gave different shoot weight depending on the food waste source of the leachate. The content of sodium and chloride in the leachates varied remarkably depending on food waste source, and it was concluded that avoidable food waste contained higher amounts than unavoidable food waste, making unavoidable food waste a more appropriate source for production of bokashi leachate fertilizer.