Written by Jon Williams from www.thesoilexpert.co.uk
An old adage of farming practice we need to pay attention to with our management of our slurry and manures for the benefit of the environment and our farm business.
With increasing attention focused on the environmental impact of food production methods currently in practice and the industrialisation of agriculture via the dependency on this development from synthetic fertilisers and chemical cocktails which can be considered as a chemical experiment, it is becoming increasingly clear that this form of food production is resulting in depleted soils, of soil life and nutrients with the result that the food produced no longer has the nutrient density or health benefits gained from a more balanced living soil system more in harmony with nature.
The current industrial model of agriculture must take a new more holistic approach considering not just the short term gains but also the longer-term impacts of such methods of production and one way to assist in this shift is to change our attitude toward slurry and manure, transforming this from a waste product into one that is an asset. The good news is that Governments are prepared to back this with financial incentives under the heading of providing “Public Goods”
The science of slurry and manure
To achieve the best outcome an understanding of the science of slurry and manure is useful and this combined with it’s impact on the soil when it is applied in different forms such as anaerobic or aerobic or fermented products.
Anaerobic digestate or slurry from a crusted or covered pit will be anaerobic and will have more volatile gases present such as Nitrous oxide, Methane, Ammonia and Hydrogen Sulphide and to overcome the immediate environmental impact of these gases it is suggested that they must be injected into the soil to reduce the impact of these gasses in the air, some of which are being blamed for creating particulate matter damaging Human lung tissue. All injection of slurries must be done when soil conditions are such that they are not holding water which will result in further damage to soil life and also soil structure.
However there is a more serious long term implication when such a product is injected into soil. Being anaerobic the pH of Digestate in particular is above 8 (ref Wrap digestate and compost use in agriculture Feb 2016) and so the product is caustic and is detrimental to soil life as it burns worms which happen to like to live in an aerobic soil and so they take a hit but can get out of the way when injected in slots.
The overall impact is that the soil is flooded with available ammonia and there is a flush of Nitrogen similar to when large amounts of fertiliser Nitrogen is applied and Rothamstead have just released the results of 40 years of research showing that the more available N that is applied to soil the more it distorts the genetic expression of soil organisms. (ref Andrew W Neal) So the overall impact of anaerobic digestate or slurry from a crusted and untreated or covered store has a negative effect resulting in the soil becoming more dependent on brought in synthetic nutrients as most of the Nitrogen is immediately available.
One alternative to this is to render the slurry to being aerobic and this can be achieved in several ways with huge benefits to the environment as well as to soil life. Firstly let’s look at what is the product we are dealing with and to understand how to manage it for our best advantage and to have the least impact on the environment. Slurry generally has a low fibre content and a high Nitrogen to Carbon ratio and is bacteria dominated with little fungi present and so in that respect it is an imbalanced product as far as the soil is concerned, however we have to make the best use of it.
The nitrogen content can vary according to the amount of protein fed to the stock producing the slurry because livestock are fairly inefficient at converting protein into meat or milk and so the higher the protein diet can produce a higher value slurry and it is therefore more worthwhile to invest in stabilising the nutrients held within that particular slurry.
One of the amendments that can be used to retain this value in our slurry is to render the product to become aerobic and this can be achieved in several ways, such as a mechanical bubbler, or by adding a catalyst such as Plocher and the result of these amendments is that as the slurry becomes aerobic the pH is dropped towards neutral with the aerobic bugs creating Carbonic acid which in turn stabilises Ammonium which becomes available for plant use in a similar form as comes from fertiliser. However not all the nitrogen is in this available form as there is a portion that is retained as Organic Nitrogen as the slurry has become a stable product and is now not breaking down further as it would in a digester. The organic Nitrogen is slowly released during the months following the application and so there is not the flush of available Nitrogen as seen from Anaerobic digestate and the plant is fed in a more natural way which can have the effect of reducing the incidence of disease and better performance if conditions become dry.
Other methods of lowering the pH of slurry are being carried out with the addition of sulphuric acid which does stabilise the nutrients via the same process of lowering the pH of the slurry but does not render the slurry to being aerobic and of course there is the health and safety issues of handling and applying such a product and its corrosive nature damaging concrete slats and retaining wall.
However there is a relatively new method of lowering the pH from about 7.2 to 6.8 which is done by the addition of” Effective Microorganisms” which encourages a fermentation of the slurry. This concept was developed in Japan by a Professor Higa in 1982 who coined the term “Effective Micro-organisms” when he discovered the mix of 80 microbes which work synergistically to ferment organic matter retaining the nutrients in a stable form. The fermentation actually pre-digests the organic matter making it immediately available to the soil organisms and thus to the plants.
This product can be used with a covered slurry pit which I understand is the proposal for management of slurry stores in England. E.M. is based on the principal of anaerobic fermentation and by lowering the pH, can retain the value of the nutrients within the slurry which when applied to the soil is already in a more mature form which allows the soil organisms to utilise it without using a lot of energy and there is no loss of volatile gasses into the environment. This treated product might no longer mean that you will be required to inject it into the soil which reduces the fossil fuel use of slurry application as well as wear and tare on machinery.
Having a different Nitrogen to Carbon ratio this product has a higher fibre level and therefore is more conducive to the establishment of a more balanced product enhancing both the Bacteria and the Fungi within the product and consequently when applied to the soil creating a more balanced soil. Currently on most farms this product is not amended in any way and under the proposed new legislation may need to be incorporated into soil with 24 hours of application. This of itself has an environmental impact by the very nature of ploughing it in there will be a further release of CO2 into the atmosphere but the aim of this protocol I suggest is to reduce the ammonia going off into the environment thus lowering its potential impact on Human health.
So from this we can assume that untreated manure releases volatile gasses including Ammonia and that there is considerable potential benefit in stabilising those nutrients. Most farms still leave manure in a heap outdoors and un covered releasing volatile gasses and allowing nutrient run-off, and even if an element of aerobic composting is carried out there is a further release of CO2 into the atmosphere with considerable losses. Therefore the way we currently manage manure needs to be considered.
These issues can all be dealt with by treating the manure with Effective Micro-organisms, known as Bokashi, which again ferments the manure stabilising the valuable nutrients including the ammonia and so the need for ploughing after application will not be necessary and manure application can be carried out on Min -tilled soils which will have multiple environmental benefits, retaining carbon as well as enhancing soil life and crop performance.
The product can be applied to the manure as it builds up in the sheds layering it by spraying it on the fresh bedding when added and the animals will tread it in creating an anaerobic bed but stabilising the Ammonia reducing it’s potential impact on animals within the sheds. Alternatively the sheds can be emptied and as the pile builds up the product can be applied in layers and then covered with a silage sheet for the fermentation to take place which is completed within 6 to 8 weeks leaving a mature product which will be soon converted into soil as it is quickly utilised by the soil life. This having a further benefit in feeding the soil Micro-Biome with a balanced product having both beneficial bacteria and fungi present and so the soil becomes less reliant for cropping with synthetic fertilisers and plants are less stressed with the potential of reduced disease.
An added benefit is having more product to spread on the land because the losses are dramatically reduced with no Co2 going off into the atmosphere during the process of maturation and there is more carbon entering the soil thus enhancing the nutrient and water holding capacity of the soil as well as achieving greater Carbon sequestration, a “Public Good.”
The micro-organisms in Bokashi can be considered as the new meaning of culture in the word agriculture and is already used by 75% of all Dutch farmers and I see no reason why it cannot achieve similar levels of use here in the UK. So a mind shift in thinking and a new attitude towards slurry and manure can result is a win, win situation both for the environment and the farmer.
Available from Agriton Ltd.