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Treating manure with microorganisms; is bokashi worth it?

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Treating manure with microorganisms; is bokashi worth it?

What is bokashi and why is it being trialled? 

In this Field Lab two farmers in Scotland have teamed up with soil expert, Audrey Litterick, Earthcare Technical, to see if there are practical benefits to using bokashi – treating manure with microorganisms that break down animal bedding and dung – over a 3-year period.  

Manures made through the bokashi process will be compared with those made using standard farming practices on both farms.  

If the reported advantages from bokashi manure treatment are true, then the process could potentially save farmers money as well as improving animal health, nutrient management and carbon footprint. If these advantages turn out to be significant, then this field lab could make the case for bokashi use to become widespread in the UK. 

On-farm research 

We joined Audrey, as she visited Glen Fincastle, one of the two trial sites. 

Andrew Barbour_Audrey Litterick
Andrew Barbour and Audrey Litterick at Glen Fincastle

Andrew Barbour’s interest in bokashi is to find a way of minimising nutrient loss from housed manure and to reduce methane and ammonia emissions from the farm: “[We wanted] to make sure we don't lose nutrients and also hopefully improve our carbon balance, which is one of the claims of bokashi in terms of reduction in methane loss ... from composted materials”.  

Another motivating factor was finding a good alternative to straw (in this case wood chip) and wanting to feed the biology in his fields and improve soil productivity. The idea behind using wood chip as bedding was to provide a good dry bed, which would hold its position in the cow shed, as opposed to straw where there is an initial build-up of material which the cows tend to push around. Seonag Barbour (Andrew’s wife) explained, “It's been very beneficial putting the wood chips down ... and we'll certainly keep on doing it".

A crucial change that they have made at Glen Fincastle is covering the manure stacks with black plastic sheeting. The combination of covering the dung heap and using bokashi should be better than regular manure practices in terms of carbon footprint – losing less methane. There should be lower losses of nitrate (and possibly potassium) through leaching too. 

Does Bokashi improve the quality of manure and increase soil health?  

Samples of the bokashi and non-bokashi manures were taken, as well as soil samples from the chosen field where the manures will be spread in early summer this year. This may help farmers understand the impact the differently treated manures will have on the soil, although it is acknowledged that many years of data would realistically be needed for a conclusive study.  

Audrey bagging samples of treated manure

Initial observations included the fact that the bokashi-treated manure does not smell like farmyard manure – Andrew explained that it is “utterly different: sweet smelling, with less ammonia and seems well broken down”. It was also immediately clear that there was more air and worms in the bokashi-treated manure. It is anticipated that the bokashi-treated manure will be easier to handle and to spread than other manures made on the farm. 

Andrew feels that animal health does not really differ between his bokashi-treated and standard bedding as the shed at Glen Fincastle is a well-aerated environment – their main focus at the moment being on retaining nutrients and trying to reduce greenhouse gas emissions. 

What changes could be expected to soil health after using bokashi? 

Andrew is hoping to improve the biological activity in the soil: “I want to improve the availability of phosphate in particular which is, I'm told, locked up in the field in unavailable form, but becomes more available with good soil biology. The fact that we seem to be able to grow reasonable grass crops with very low phosphate levels suggests that something [positive] is going on”. 

Soil sampling in the field where the manures will be spread

Audrey agreed that this suggested that there was good fungal activity – good mycorrhizal associations – and with small regular additions of organic matter, that should continue. 

Andrew confirmed that this is what he was hoping for: “With the wood chip, you are bringing a little bit of P and K, extra material in from outside of the field environment and adding that organic matter to the field. So, it's a sort of translocation, it's circular within the business, within the landscape". 

How does the time and cost spent on treating manure with bokashi compare to what was involved before? 

At Glen Fincastle the covering of the treated and untreated manure stacks with plastic has been a crucial step which they will carry on doing. Andrew believes the financial implications are minor compared with the benefit he anticipates getting out on the fields as well as having a nicer product to handle. 

The bokashi treatment goes on at the beginning and the end: “The effort involved is half an hour at the start and a little more at the end, but it's not a big thing – the actual hassle of it is zilch”. 

At Glen Fincastle they have been learning as they go – ordering more covers, and covers that are bigger than the piles of manure so that the piles can be effectively weighed down with tyres to prevent the covers from blowing off in the wind. It's early days and the results are still to come, “but right where I sit just now, I would envisage us carrying on with bokashi outside of this project”. 

Is bokashi better for a farm’s carbon footprint? 

Audrey advises that “in theory bokashi manure treatment should mean losing less nitrogen as nitrate and potentially also as nitrous oxide because there will be less movement of cattle around wet, uncovered edges of middens. It should also result in lower ammonia emissions (although ammonia is not a greenhouse gas) and lower losses of other soluble nutrients such as potassium and sulphur. We already know that there are several benefits from covering dung heaps”. 

Covered, treated manure

The impact on manure practice as a whole 

Audrey explains that there is very clear evidence to show that bokashi-treated manure is superior to composting manures without it. Farmyard manures do not compost easily or well, and the effort and cost involved in composting manures properly is significant. “You'll lose about half of the mass in a dung pile and a great deal of valuable organic matter/carbon if you compost it. It’s very clear that bokashi is a better way to go.” 

Tips for farmers looking to use bokashi manure treatment on their farm 

In their situation at Glen Fincastle, Andrew explains, “Basically we are trying to ensure that the environment that develops in the bedding in our animal housing is conducive to the bokashi bugs being able to do their job. And if we can restrict it to one great big spraying at the beginning and another great big spraying at the end, then it all becomes believable financially.”

Covered dung heaps

Andrew also believes that possibly the biggest consideration is not the applying of the bokashi but the covering of the heaps with plastic which most people are not used to doing, but is essential for the process to take place. He advises that if you had a digger on the farm you would dig in one side of the plastic on the windward side to protect it from storms and high wind, or have bays for the dung (which need minimal weighing down). 

Is bokashi worth it?  

The trial results will not be available until 2026 but, at Glen Fincastle, Andrew Barbour strongly suspects that they will carry on using bokashi: “The cost would not be a huge barrier if you are getting benefit on the fields and a nicer product to handle ... I'm also conscious that, where we are in our working life, if we set up a routine procedure for the next generation coming along there’s a great chance they'll carry on doing it. So if it does turn out to have benefits from the greenhouse gas side of things, great, and it may make life easier for them with all the other changes that might have had to be made if they're already doing it”. 

Follow the latest from the field lab here