Black Soldier Fly Processed Food Scrap | Foliant and Soil Applications : The Life and Times of BSF (Black Soldier Flies)
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Black Soldier Fly Processed Food Scrap | Foliant and Soil Applications

by Terry Green on 11/15/12

Larvae of the Black Soldier Fly (BSF) are extraordinarily efficient in recycling vegetal and food scrap wastes back into the environment. They help accelerate the conversion of organic wastes into valuable earth-friendly products while also reducing the amount of pollutants given off during the decomposition process. The liquid fraction released as the organic waste gets recycled, a leachate of the decomposition process, can be used by gardeners as a foliar spray, and soil conditioner, in stimulating the growth of plants.

Decaying vegetal and food scrap wastes produce volatile fatty acids, acetic acid (vinegar), fragemented carbohydrates, alcohols and other fermentation byproducts in the course of getting broken down and mineralized. These byproducts form through a combination of aerobic and anaerobic microbial activity occurring spontaneously as waste undergoes biological decomposition and mineralization, and end up in the leachate (liquid) fraction released as the waste decomposes.

Not all of these byproducts are beneficial to plants and soil, however, and some are known phytotoxic agents. They can cause stunted or delayed growth of plants when added in excess amounts to the soil. Evidence of their presence, aside from chemical analysis, can be seen by noting poor root growth or failure of seeds to sprout in soil enriched with too much organic matter. Excess acids and alcohols accumulating in leachates can also shut down microbial activity in compost bins, and likewise disrupt beneficial microbial activity in soils upon addition of the leachate directly to soil in an undiluted state.

To avoid the negative inhibitory effect of adding compost leachates directly to soils, they should be diluted in water at the very minimum at least 10-fold (1 part compost liquid mixed with 9 parts water), better yet, 50-fold or greater, if practical, to be on the safe side.  If possible, also check the pH of the liquid to make certain its pH is > 6 and, if necessary, dilute the liquid further to ensure that the solution you apply to your soil is not too acidic. As a general rule, compost liquids left untreated become quite acidic, often reaching a pH in the range of 3.5 to 4.5.

image of growth stimulation of bsf leachate applied to fountain grass
Figure 1. Effect of varying dilutions of BSF-treated leachate on the growth of Fountain Grass cuttings grown in potting soil relative to control plants left untreated. Copyright(c) 2012, Terry Green, All rights reserved.

Figure 1 shows the effect of applying leachates recovered from food scrap wastes recycled and processed using BSF larvae on Fountain Grass. In these studies the average growth of potted Fountain Grass plants was tracked in triplicate sets of experiments over the course of approximately 50 days following pruning of leaves of the plant within 5 cm of the root stock, pairing back the roots, and transferring the plants into fresh potting soil at the beginning of the study.

In a separate series of field tests, the effects of foliar spraying and watering of selected vegetal plants once weekly over approximately a 50 day interval starting after the first week of transplanting vegetal plants into soil plots was examined and is summarized in the table below (Fig. 2).  Indices highlighted indicate that the BSF-treated leachates have a significant foliar stimulatory effect in addition to growth stimulating activity when applied directly to soil under field trial conditions.

image of summary table of BSF leachate growth stimulating effect on plants
Fig. 2. Field test results on weekly applications of BSF-treated food scrap leachate on selected vegetal plants grown in soil following weekly applications relative to control plants unexposed to the leachate treatment. Copyright(c) 2012, Terry Green, All rights reserved.

Not all plants show a response. The appropriate dilution of leachate may in some instances need to be adjusted for optimal outcomes depending upon the particular plant receiving an application.

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