Despite its name, Bokashi composting is a fermentation process for handling kitchen scraps right in the home. It is fairly easy to do and produces few odors. The majority of the material ends up as fermented kitchen scraps and some is drained out the bottom as a brown liquid, commonly called Bokashi tea or Bokashi leachate. Advocates of this process claim that the Bokashi tea is a good fertilizer, full of all the nutrients your plants need.
In my previous discussion about Bokashi, I speculated that the tea contained few nutrients. At the time I found no chemical analysis of Bokashi tea, not even from proponents of the process. One of my readers has now found such a study and I will have a close look at the data in this post.
What is Bokashi Composting?
The process is called Bokashi composting, but in reality it is not a composting process. As discussed in my previous post, this is a fermentation process. It pickles the food scraps and the end product is called Bokashi ferment which is then added to a compost pile, or incorporated into soil to start the real composting process.
The excess water and juice from the food scraps migrates to the bottom of the Bokashi pail, and are drained away to prevent the fermenting material from getting too wet. This liquid is called Bokashi tea, or Bokashi leachate.
Chemical Analysis of Bokashi Tea
In this study, kitchen scraps were obtained from several places including a home, and I am going to use that data since it is more representative of the material a gardener would process. The collected material was then fermented in a lab location so they could control the environment. The table above shows nutrient levels in pure Bokashi tea (concentrate) and the diluted form (middle column) which is 2% of the concentrate. The 2% value is considered high by the researchers, whereas 1% is considered low.
To compare this to normal fertilizer values, I have added the values for the MSU fertilizer which is used for growing a wide range of plants including orchids.
Note that the above table shows the macronutrients in mg/l and the micronutrients in ug/l. The values for the MSU fertilizer have been converted to element mass numbers to match the ones reported in the research (ie P values instead of P2O5).
Nitrogen levels in Bokashi tea are very low. Phosphorus and potassium are on the high side.
The level of several micronutrients are also very low.
Levels of Sodium and Chloride
In addition to the plant nutrients reported above, the Bokashi tea also had high levels of sodium (1200 mg/l) and chloride (4300 mg/l). Once diluted to the 2% level used in the above table, the leachate will have a sodium value of 24, with 50 being toxic to plants. The chloride is at 85 mg/l and a value of 70 is considered toxic.
Much of the sodium chloride would be from salt added during cooking, or salt added as a preservative in commercial food. People using Bokashi leachate on plants should be careful which food they process.
Growing Plants With Bokashi Tea
The study also tried growing pak choi in a number of different medias using both Bokashi tea and standard fertilizer.
Plant growth using Bokashi tea was much slower than control plants, in both sand and peat substrates. It is assumed that this is largely due to the very low nitrogen levels.
“The low concentration of inorganic nitrogen in the leachates can be assumed to be due to denitrification processes taking place during the fermentation, as the food waste was kept anaerobically in air-tight containers, thereby promoting denitrifying bacteria. ”
Should You Use Bokashi Tea as a Fertilizer?
Bokashi tea could be used as a fertilizer if additional nitrogen is added. Without the added nitrogen, it is a poor fertilizer at best and at worst, the high sodium chloride could be toxic to plants.
I would not recommend it for use on potted plants. Add it to the garden where additional nitrogen might be available, and where excess sodium is easily washed away.
It should be diluted to at least 1% to ensure the sodium chloride levels are not toxic.
So bokashi diluted to 1-2% ( ratio 100:1) (npk1:3:14)with ratio 10:1 urine (npk 11:1:2) ( add some bone meal for phosphorus (npk 3:15:0))would be a great tea, then further compost the bokashi as the nitrogen factor/layer of traditional aerobic compost. Or directly bury it.
Save your salty, dairies and meats for a black soldier fly bin (chicken feed) or worm farm. If you have either.
Does anyone know if Bokashi liquid will react with bone meal to make P available to plants faster? Thanks!
Bokashi leachate has a pH of about 5, so yes it should solubilize the phosphate.
Appreciated the article, after reading so much in favour of Bokashi this is fresh air.
To stop another myth. Denitrification is a false deduction. Bokashi leachate contains little nitrogen because most of the input N is still in the fermenting bin. It will reach the soil from there. The main point of bokashi is the food, not the sauce!
Nitrogen is essential to build protein molecules. That’s what makes it a macronutrient. Protein molecules are complex and do not break down in lacto-fermentation, which does nothing but convert a (small?) fraction of the carbohydrates: C6H12O6 -> 2 C3H6O3 (lactic acid). Proteins, fats and remaining carbs stay largely intact.
Molecules added to the soil will be broken down by many microorganism species, the most important of which in this context are the nitrogen releasers and fixers. These are natives; they do not come via EM but are the true effective microorganisms in the end-to-end bokashi process.
So if you want to bust a bokashi myth, ask what all the non-lacto-fermenting species in EM actually do, if indeed they survive at all. I think they were selected for Higa’s ideas to feed bacteria direct to soil and livestock, and are of questionable value in the context of preparing food waste for consumption by soil life. Expensive, carbon-emitting freeloaders.
My guess is that the proportions of elements in leachate represent free molecules from cytoplasm released by cell breakdown, plus some lactic acid / lactate.
The amount of nitrogen in the leachate is in the table.
Nitrogen fixing bacteria are not going to play a significant role in decomposing the ferment.
That is a helpful table. I wanted to point out that some people (including some here?) misinterpret its low N content as evidence of denitrification in the bokashi ferment, which is the opposite to what happens. Bokashi is just like any other lacto-fermented food: mildly acidic (to us); softened, preserved, but not broken down. Its protein is basically intact (or else every food nutritional study is wrong!) so the nitrogen remains.
Yes, nitrogen fixers may not decompose the food. What they (and some phosphorus solubilizers) definitely do is bloom when pure lactic acid is added to soil – see Rodríguez-Morgado et al (2017) Effect of L-lactic acid from whey wastes on enzyme activities and bacterial diversity of soil, Biology and Fertility of Soils 53:389–396.
I should add they bloom “as long as water is present” because that is necessary and sufficient for lactic acid to convert to lactate, which is what they actually consume. There may be enough water in the leachate, but I always dilute it before addition to soil. In dry conditions water is essential, certainly for leachate and probably before adding bokashi food too.
Why does this matter? Because blooming native soil bacteria are the true effective microorganisms in the end-to-end bokashi process. They increase soil microbial biomass significantly, an average 60% in one MSc project. When the food runs out excess biomass dies, feeds worms (etc) and becomes soil organic matter. Apart from its homolactic fermenting bacteria, I believe that the EM bran is worthless except as a few extra food scraps for the natives. See Mayer et al (2010) https://doi.org/10.1016/j.apsoil.2010.08.007
I agree with much of what you say. I compare bokashi to ensilaging which seems to produce the same ferment product without the addition of EM.
Everything I have looked at regarding bokashi, compost and especially compost tea seems to conclude that the added microbes add very little value to soil. Thanks for the last link.
Bokashi is a relative of ensilaging, yes, but their end products differ because their inputs differ. As far as I can ascertain, silage does not make a great soil amendment.
To understand why, I think we need look no further than the nutrient content of food waste. In aggregate it must be one of the richest and most balanced diets imaginable, with a wider variety of proteins, carbs and (significantly?) micronutrients, plus the high energy content of fats. Add lactate and no wonder the soil life blooms!
“silage does not make a great soil amendment” – actually it does. Hay used as mulch is great for developing good soil. Hay is also fed to animals which turnings into manure which is considered to be a great soil amendment.
Keep in mind that most kitchen scraps is mostly water. To compare nutrient values you would have to compare dry weight numbers.
Hay is not silage until fermented.
IMO anything green used as mulch is good for soil and cut-and-drop is better than gathering for compost, because decomposition is almost all aerobic and the soil is shielded from erosion and evaporation.
Fresh greens contain too much moisture for either ensilage or bokashi if they are the major input. Less than 20% dry matter diverts into a butyric fermentation instead of lactic. I know a student experiment did that because they used too much cabbage. You don’t want the result and neither do your cows or your soil life!
The CSIRO advises farmers to wilt grass for 36 hours before ensilage, or until 30% dry matter can be measured. A study across all parts of Wales found that the average food waste was just over 25% dry matter. Since I’ve never had a batch of bokashi go butyric I guess that’s a safe level.
An interesting aside: the below 1% average nitrogen content of Welsh food waste equates to about 3.5% dry matter. That’s half of an artificial NPK like Growmore, which suggests that bokashi has a good nitrogen replacement fertiliser value.