WHERE THERE’S MUCK THERE’S BRASS!! 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.
Slurry 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 8 DIRECT DRILLER MAGAZINE
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
ISSUE 13 | APRIL 2021
