This innovative project, led by Daniel McKay Fletcher at SRUC, was one of 16 scoping studies to receive funding from the AFN Network+. Here he explains why his team plans to create a web tool to help farmers forecast the greenhouse gas emissions from their manure.

Rearing cattle significantly contributes to global warming due to the emissions of potent greenhouse gases such as nitrous oxide (released from manure storage, fertilising crops/pasture and the soil) and methane (from cows burping and farting, and from manure storage). Methane and nitrous oxide are thought to warm 27 and 265 times more than carbon dioxide respectively. As a result emissions from the storage of manure from all livestock in the UK is estimated to make up 16% of the global warming potential of our agricultural emissions.

Although manure is a big emitter of greenhouse gases, it is also a valuable resource for farmers. It can be used as an organic fertiliser, reducing the need for synthetic fertilisers, which are expensive and emit high quantities of carbon dioxide during production, while increasing soil carbon storage. However, the release of gases from manure during storage reduces the fertility of the manure once
it’s applied to the field. Our project will address this challenge by co-designing a web-tool with farmers and consultants. The tool will forecast greenhouse gas emissions from manure to provide farmers with information to make effective decisions to minimise emissions and increase manure fertility. It will also raise awareness of how large emissions from manure can be.

Calculating emissions

​The microbes, which are responsible for the emissions of methane from manure, thrive in warm conditions, so emissions are much higher when manure is stored over warm periods. Additionally, the quantity of manure stored is uneven throughout the year because farmers move cattle from barns to pasture (emissions from manure on the field are much lower than when stored) and spread the manure as fertiliser. Typically, methods for calculating manure emissions multiply the amount of manure generated in a year by a factor which depends on the average temperature in the UK. This approach overlooks the possible periods of high emissions when large amounts of manure is stored during periods of high temperature. As the effects of global warming become more apparent, these hot periods may become more frequent and have a noticeable impact on emissions.

How it will work

To address this, the web-tool developed in this project estimates the volume of manure stored at a given time based on farmer inputs (such as cattle numbers, milk production and feed quality). It will also estimate the activity of the methane generating microbes, based on the weather forecast on the farm. This will lead to a  more accurate prediction of manure methane emissions.

An example display of the current version of the web-tool for a hypothetical dairy farm in Dumfries and Galloway can be seen in the image below. The latitude and longitude define the location of the farm to determine the temperature. The number of cows, the milk yield and digestible energy (quality of the feed) help determine how much manure is being generated on the farm. Date in and date out refer to when the cows were brought inside the barn and let outside and determine where the manure ends up (on the field or in manure storage). ‘Date slurry was emptied’, defines the start of the simulation from when the slurry store was last emptied. Finally length of simulation defines how long the farmer would like the forecast to run from ‘Date slurry was emptied’.

The graph shows how much methane is being emitted on each day (kgCH4/day). In winter, we can see emissions are low due to the cold weather and because there is very little manure being stored (manure was emptied on the 1st of January). However, as it gets warmer in spring and storage of manure increases, we can see emissions start to rise. In June, when we had very warm weather, emissions reached a peak of 20kg of methane on the 18th ; the equivalent greenhouse gas emissions of driving a petrol car for 1,400 miles for this day alone.

The developers of this web-tool are academics and don’t have much farming experience, so in this AFN Network+ Scoping Study project we will work with dairy farmers and consultants to get feedback on how we can make this tool easier to use, capture relevant management decisions, and ultimately help farmers make decisions which can reduce emissions from manure. By the end of the project we hope to have a new and improved version of the web-tool which has integrated the feedback.

Other project members include Alexander Pirie, SAC; Steve Anthony, ADAS; Vera Eory, SRUC; Yang Lu, York St. John University