According to calculations by Kite Consulting, 23% of a dairy farm’s carbon footprint comes from nitrous oxide (N2O). The rest comes from methane (52%) and carbon dioxide (25%). Nitrous oxide is a particularly potent gas when it comes to global warming – it is 296 times more powerful than carbon dioxide – and minimising emissions is one of the main ways of substantially reducing the carbon footprint for milk.
Nitrous oxide is generated by the microbial breakdown of nitrate in the soil. It doesn’t matter whether this nitrate originates from manure or artificial fertiliser. So good grassland management practices and ensuring the timely and accurate application of fertilisers go a long way to mitigate losses.
“The good news is these practices are financially beneficial for farmers,” says Kite consultant Helen Evans. “In this case, helping save the environment goes hand in hand with saving money.”
For those farmers who view muck and slurry as an irritating consequence of livestock production – and many do – the starting point for carbon-friendlier farming is to reassess that view, she says. Making best use of manures is one of the main ways of reducing nitrous oxide losses.
In a typical 6% dry matter cubic metre of dairy cow slurry, there is about 3kg of nitrogen, 1.2kg of potassium and 3.5kg of potash. But it is not necessarily the amount that matters – it’s the availability. Potassium and potash availability remains pretty constant at 0.6kg of P and 3.2kg of K, but nitrogen availability can vary from 5% to 35% depending on the time of year the slurry is spread, the temperature and other factors. Spreading it in spring maximises nitrogen availability and minimises nitrogen cycle losses. Spreading in autumn results in the least availability and highest losses.
“Maximising application times of slurry could mean the typical output of a 650kg Holstein cow over a six-month housed period is worth as much as 58kg of nitrogen in weight terms, which is the equivalent of 168kg of 34.5% nitrogen fertiliser, with a value of between £19 and £28,” she says.
“Kite has many dairy farmer clients who are becoming far less reliant on artificial fertiliser by making best use of muck and slurry and, in so doing, are reducing their farm’s carbon footprint. Some have more than halved their artificial fertiliser use.”
The method of slurry application also helps reduce nitrous oxide losses. “Nitrogen cycle losses are far less if the slurry is injected compared to when it is just spread on the land,” she says.
Ms Evans advises injecting in spring and after first-cut silage and on grazing land during the season. When the operator makes a good job of injection cows can graze land far quicker than if slurry had been spread. “Again there is a logical business reason for injecting as well as there being an environmental benefit,” she says.
Making better use of clover in grassland swards will also reduce a farm’s carbon footprint as clover mops up nitrogen from the atmosphere and re-fixes it back into the ground. It is an easy carbon friendly change to make. A good stand of clover can fix between 150 and 200kg of nitrogen a hectare, she estimates.
“Using clover increases the output of the sward in mid and late season and improves intake and animal performance so, again, it has positive benefits. Organic farms are a shining example of this, and there is a lot conventional farms could learn from them.”
For those looking to increase clover she advocates using a tined grass harrow with a seedbox after a sward is established to enable a cheaper herbicide to be used before the clover is drilled.
“The management practices we advocate to reduce a farm’s carbon footprint are fairly easy, logical and financially beneficial to adopt,” she says. “There are simple changes to pasture management that can be made which will have financial benefits for farmers and positive benefits on the environment.”