Case study - reducing greenhouse gas emissions

Published 28 June 10

David Munday milks a 175 strong autumn calving Holstein herd at Town Barton Farm near Crediton in Devon. The soil type is a sandy clay loam which is well suited to grassland and arable cropping and of the farms 136 ha 40ha of both forage maize and winter wheat are grown. The remainder of the farm is down to grass.

The cows have an average yield of 8,000 litres per cow and are housed in cubicles in the winter and encouraged to produce maximum milk from grass during the spring and summer months.

There are some key areas of the farming system at Town Barton Farm that are helping to reduce greenhouse gas emission by good practice.

"Many of the things we are doing to reduce our greenhouse gas emission not only make environmental sense but make financial sense too," explains David Munday.

"We've made some steps to cut fuel and energy costs which will in turn cut carbon dioxide emissions from the farm. Cows are encouraged to graze for as long as possible during the year, reducing the amount of silage needed and slurry that has to be spread. Slurry channels and automatic scrapers in the cubicles reduce the amount of energy used to manage slurry.

"The high forage ration throughout the year reduces the amount of purchased feed being transported to the farm," he continues. "We practice minimum tillage, wheat is direct drilled into maize stubble, reducing the number of tractor passes."

The dairy cow ration is formulated to contain lower levels of protein than would normally be the case for high genetic merit Holsteins.

"The logic behind the lower protein diet is that peak milk yields will be reduced, cows will be under less production pressure and as a result produce lower cost milk and last longer in the herd," David explains. "The maize silage is naturally low in protein and is fed with grass silage and a blend of soya/rapeseed meal complimented with dairy cake of between 2 and 6kg/day depending on the stage of lactation. The protein percentage of the complete diet works out at 15 - 16%." 



Maize silage


Grass silage


Rape/soya 50:50 blend




Nutrient wastage is minimised by avoiding excess protein in the diet and the amount of Nitrogen excreted by the cows is reduced. A secondary benefit is that less imported protein is needed, saving the business money and reducing greenhouse gas emissions associated with concentrate feed production and transport. 

Farm yard manure (FYM) is either stored in sheds or on a concrete pad and slurry produced by the milking herd is stored in the concrete slurry lagoon. Allowing the formation of an undisturbed crust on the slurry store reduces ammonia emissions, and more nitrogen is retained in the store that can potentially be used by the crop, thereby reducing the need for purchased fertiliser.

Both FYM and slurry are used to provide nutrients for growing crops on the farm. Standard values for nutrient content are used for managing FYM, but slurry is analysed every four years. The farm has the following nutrient management policy:

  • As the majority of the grassland is used for cattle grazing, slurry and FYM are targeted towards the arable land which has a two year rotation of maize followed by wheat.
  • As FYM has a higher concentration of nutrients than slurry, and is therefore more economic to transport, it is applied to fields furthest away from the farm.
  • All spring applications of FYM and slurry are rapidly incorporated into the soil. By ploughing in manure quickly, ammonia emissions are decreased and N utilisation maximised.
  • FYM or slurry is applied to maize fields to provide nutrients for the maize and following winter wheat crop.

"By taking better account of the nutrients in manures over the last 10 years, not only have manufactured fertiliser purchases fallen, but maize crops mature more consistently throughout the field, improving maize silage quality," says David. "For the arable crops, no potash fertiliser is purchased and only a little phosphate is used as a starter fertiliser for the maize."

By allowing for the nutrients contained within the manures, the farm has saved over £200/ha, and over £8000 across the 40ha of maize. Similarly by allowing for the nutrients in manures, fertiliser costs for the wheat crop have been reduced from £273/ha to £198/ha, saving a total of £3,000 per year over the 40ha of wheat grown. 

Trees, hedges and permanent pasture can all act as stores for carbon on the farm. The policy at Town Barton Farm is to maintain hedges under Countryside and Entry Level Stewardship schemes, as hedges are only cut one year in three. A proportion of the farm is maintained as permanent pasture that has never been ploughed and is a good store of carbon.

Strengths at Town Barton Farm

  • Good use of nutrients in manures reduces manufactured fertiliser use and helps to reduce GHG emissions associated with fertiliser manufacture and transport
  • Regular soil and manure testing to better match crop requirements and nutrient applications leads to lower ammonia and nitrous oxide emissions
  • Low protein cow diet reduces N surplus on the farm
  • Natural crust on slurry store reduces ammonia emissions
  • Farm infrastructure and focus on maximising grass intake results in energy savings onslurry handling, silage making and feeding as less conserved forage is needed - all leading to less carbon dioxide produced from machinery.

But more could be done…

Opportunities at Town Barton Farm

  • Self feeding of silage in winter would reduces machinery sourced carbon dioxide emissions
  • Reducing the winter housing period would cutassociated GHG and ammonia emissions from silage production and handling slurry
  • Using low ammonia emission spreading machines for slurry applications to grassland (injection/trailing shoe) would reduce ammonia emissions and increase efficiency of use of slurry N
  • Increasing cow longevity though better breeding would result in reduced GHG emissions per litre of milk
  • On farm anaerobic digestion of manures reduces methane losses, but capital costs remain a barrier
  • Reducing cow replacement rate associated with mastitis and feet problems. 

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