Case Study: Seques­tering carbon in the dairy sector

Working in part­ner­ship, Rose­mary and Joe Colling­born run a care­fully bred, closed herd of 130 pedi­gree Friesen cows at Hill End Farm near Chip­penham. Their 68ha farm is ecolog­i­cally managed to create harmony between commer­cial produc­tion and conser­va­tion. “We have purpose­fully bred a cow that thrives on a grass-based system and produces a good yield with excel­lent quality from forage,” says Mrs Colling­born.

The cows are rota­tion­ally grazed on perma­nent pasture and long-term leys – producing an average lacta­tion of 7,625 litres, with butterfat and protein at 4.3% and 3.3%, respec­tively. Around half of the milk is produced from forage.

Rose­mary Colling­born is a passionate advo­cate of British dairy farming.

Seques­tering carbon with soil

For over 30 years the Colling­borns have farmed sympa­thet­i­cally to the envi­ron­ment and soil carbon; including planting 1,400 trees, main­taining perma­nent pasture and reducing soil distur­bance.

“The dairy sector and grass-based systems are receiving a lot of flak over their carbon emis­sions,” says Mrs Colling­born, who finds such misin­for­ma­tion very frus­trating. “I don’t under­stand how they have got it so wrong. Live­stock farming – like dairying on a grass­land farm – is a very effec­tive way of producing food in a way which bene­fits the envi­ron­ment and has the poten­tial to sequester carbon.”

Working with King­shay

So after reading Kingshay’s work on SOC, she contacted her local water company – Wessex Water – to help work on the project with them. “Wessex Water were very inter­ested and agreed, and King­shay started analysing the samples in August this year,” she says.

“I thought it would be a very effec­tive way of producing the evidence that dispels myths and backs up the posi­tive message that grass-based systems are key for carbon seques­tra­tion and climate change miti­ga­tion.”

Eval­u­a­tion of the soil samples

Soil samples from a third of the farm were sent for CarbonCheck analysis and textural clas­si­fi­ca­tion. Clay content ranged from 48% to 61% and the SOC content followed the clay, ranging from 6.7% to 8.8%.

From this the SOC/clay ratio was calcu­lated, yielding a posi­tive reflec­tion of the couple’s grass­land manage­ment, ranging from 0.121 to 0.16. All fields bar one were cate­gory indexed as very good; achieving a SOC/clay ratio greater than 0.125 – but the lower performing field still indexed as good (> 0.1 but <0.125).

The team then bench­marked Hill End Farm against the 100 UK farms sampled under the King­shay SOC project; 85% of its samples were very good, compared to the survey average of 50%.

The Colling­borns want to create harmony between commer­cial produc­tion and conser­va­tion.

Based on the farm’s soil bulk density – and with zero stones in the top 15cm profile – they calcu­lated its carbon stocks to average 91.14t/ha, with a range from 79.4t/ha to 99t/ha. That’s well above the UK average of 61t/ha.

Using the knowl­edge about the soil

So how can the Colling­borns use the analysis report? “The analysis has given us a much greater aware­ness of our soils and their ability to sequester and retain carbon,” says Mrs Colling­born. “We can use what we know to make informed deci­sions. “And crucially, it backs up the message that managed grass­land is very impor­tant in combat­ting climate change.”

The Colling­borns have recently intro­duced plate metering to better manage the grazing plat­form, maximise forage and minimise soil damage.

The report advised two main actions to help reduce carbon losses: Minimise soil distur­bance and avoid soil degra­da­tion. 

The Colling­borns have already minimised field oper­a­tions when reseeding by using minimum tillage. And they have stitched in white clover to silage leys to help fix nitrogen and increase the C:N ratio – bolstering soil carbon reten­tion.

Maximise forage, minimise soil damage

For the past 20 years they have rota­tion­ally grazed their cows –and have recently intro­duced plate metering to better manage the grazing plat­form, maximise forage and minimise soil damage. “Cows are grazed for one to two days and then moved on – they go in with the grass at 2,800kg DM/ha and are moved out at 1,600kg DM/ha – and fields are rested for 21 days,” explains Mrs Colling­born.

The farm also composts its farm­yard manure to maximise nutrient value and avail­ability, and main­tain or build SOM and SOC levels, with soil testing every three to five years. “Testing is very worth­while – but it isn’t without cost. Our milk processor is looking at carbon testing and it could be some­thing it funds in the future – it would be great if proces­sors assisted with these costs as it could be very bene­fi­cial for them as well as the farmer.”