Composting dairy slurry

Slurry and manures are valuable farm resources, but their nutrients are labile, causing emissions and pollution, including nitrate leaching. This proposal will assess the potential for composting dairy farm manure, treating dirty water separately and thereby building circularity into the farming system. Carbon sources from the farm will be used to compost manure, stabilising the nutrients and producing a more balanced and beneficial fertiliser. The project will test different forms of composting, monitor the nutrient profiles of the composts, slurry and dirty water, as well as measure the emissions produced during composting, storage and spreading, compared to slurry. Ultimately, the outputs will be used to assess the potential for treating dirty water with a farm-based Wetland Ecosystem Treatment (WET) system.

Firstly, manure from scraped yards will be taken away from the slurry system and combined with carbon sources (farmyard manure, woodchip from pollarded willows, and coppiced hedges) to produce a composted substrate. We hypothesise that this process will stabilize nutrients in a biological form that can be used as a soil improver, with lower risk of nitrate leaching and run off, compared to slurry. The project will assess different ways of composting the manure and measure the nutrient profile changes over time. Two main composting systems will be trialed; Bokashi and a traditional turned system. We aim to understand the optimal ratio and type of ingredients for composting with minimal negative effects and optimal nutrient profiles for soil health and fertility. This will be conducted via field experiments on farm and laboratory analysis at the Royal Agricultural University, alongside a literature review to understand current practices and their applicability to this system.

The second part of the project will start in the first year but continue beyond the duration of the project, and will investigate use of the liquid fraction from manure when the solid manure has been removed. The aim is to take all/most of the nutrients from this liquid for use in the composting process. The remaining dirty water will then run through a cleansing wetland system incorporating willows that would be coppiced for use in the composting process. Investigation is needed to see how this liquid fraction can be treated in a wetland system as under the current regulatory frame work any liquid that has been in contact with manure is considered subject to environmental regulation as slurry.