Category: Insights

The role of soil carbon in natural climate solutions – new paper released

Posted on April 6, 2020 by - Insights

A new paper has been released in Nature Sustainability this month which highlights the potential for soil carbon sequestration as a climate solution. You can access the full paper here. The abstract is below.

Mitigating climate change requires clean energy and the removal of atmospheric carbon. Building soil carbon is an appealing way to increase carbon sinks and reduce emissions owing to the associated benefits to agriculture. However, the practical implementation of soil carbon climate strategies lags behind the potential, partly because we lack clarity around the magnitude of opportunity and how to capitalize on it. Here we quantify the role of soil carbon in natural (land-based) climate solutions and review some of the project design mechanisms available to tap into the potential. We show that soil carbon represents 25% of the potential of natural climate solutions (total potential, 23.8 Gt of CO2-equivalent per year), of which 40% is protection of existing soil carbon and 60% is rebuilding depleted stocks.

Soil carbon comprises 9% of the mitigation potential of forests, 72% for wetlands and 47% for agriculture and grasslands.

Soil carbon is important to land-based efforts to prevent carbon emissions, remove atmospheric carbon dioxide and deliver ecosystem services in addition to climate mitigation.

Grazing experiment shows the benefit of white clover inclusion in grassland for GHG emissions

Posted on June 18, 2020 by - Insights

Source: Rothamsted Research News article, 5th June 2020

Direct emissions of a powerful greenhouse gas from certain pasture types are lower than previously thought – meaning the climate impact of grass-fed cattle herds may be overestimated.

A team from Rothamsted have shown urine from animals reared on pasture where white clover grows – a plant commonly sown onto grazing land to reduce the need for additional nitrogen fertiliser – results in just over half the amount of nitrous oxide previously assumed by scientists to be released.

Nitrous oxide is a potent greenhouse gas that is 265 times more harmful than CO2 and can account for 40% of beef supply chain emissions, and the group say these findings may help farming achieve its ‘net zero’ ambition by 2040.

In perhaps the most realistic re-creation of real farming practices to date, the researchers measured emissions from just one herd on their experimental beef and sheep farm in Devon, whereas most studies looking at the emissions from livestock arrive at their conclusions by combining data from a variety of experimental systems in addition to some estimated values.

Atmospheric chemist, nitrous oxide expert and co-author of the study, Dr Laura Cardenas said such estimates are currently provided by the Intergovernmental Panel on Climate Change (IPCC) to scientists wishing to include it in their calculations on the climate impact of our food supply chains.

She said: “Due to technical and logistical challenges, field experiments which measure losses of nitrous oxide from soils usually add livestock faeces and urine they have sourced from other farms or other parts of the farm, meaning that the emissions captured do not necessarily represent the true emissions generated by the animals consuming the pasture.”

Writing in the journal Agriculture, Ecosystems and Environment, the team report how they created a near ‘closed’ system whereby the circular flow of nitrogen from soil to forage to cattle and, ultimately, back to soil again, could be monitored.

The research was carried out at Rothamsted’s ‘farm lab’, the North Wyke Farm Platform, a unique facility where all relevant environmental, agricultural and economic data related to livestock farming are collected 24/7.

For this experiment, herds of 30 cattle were grazed on either land that had long been pasture; a high-sugar grass commonly sown by farmers; or a high sugar grass and white clover mix.

Lead author of the study, Dr Graham McAuliffe and colleagues had previously discovered system-wide reductions of greenhouse gas emissions associated with the inclusion of white clover in pasture. This conclusion was primarily driven by a lack of need for ammonium nitrate fertiliser, whose production and application create greenhouse gases.

However, in the absence of evidence at that time, the team relied on figures provided by the IPCC which assume all cattle urine or faeces deposited to soils cause the same volume of nitrogen-based emissions irrespective of pasture type.

The most recent IPCC figures provided to scientists estimate this ‘emission factor’ as 0.77%. However, the Rothamsted team’s latest experiment found it was 0.44% on the white clover-high sugar grass mix, once the additional nitrogen captured from the air by clover was accounted for.

Dr McAuliffe said: “These differences might not sound like much, but when used in calculations of the climate impact of beef, they have a considerable effect as nitrous oxide emissions can account for over 40% of entire supply-chain greenhouse gas losses.”

This new research is the first time Rothamsted scientists have quantified the climate-change related benefits of white clover, achieved both directly through lower nitrous oxide released at pasture, and indirectly by lower fertiliser requirements.

According to Dr Cardenas, further research is required to explain the detailed mechanisms behind the observed complementarity between white clover and high sugar grasses – but that the data point towards an effect of sowing clover on the soil’s microbes.

“The evidence suggests that including white clover amongst high sugar grass decreases the abundance of microbial genes associated with nitrous oxide production compared with microbial communities observed under just high sugar grass.”

As the UK strives to achieve cross-industry net-zero carbon emissions by mid-century, improving our understanding of greenhouse gas emissions and mitigation potentials has never been more important, she added.

“Although white clover is unlikely to be a ‘silver bullet’ for agriculture’s net-zero ambitions on its own, adopting combinations of multiple emissions-abatement interventions, such as increasing legume-inclusion in pasture compositions and utilisation of ‘low-carbon’ fertilisers, will be essential to maximise farming’s national and international contribution to a cooler planet.”

Soil Farmer of the Year 2020 Farm Walk with John Martin

Posted on September 23, 2020 by - Insights, Soil Farmer of the Year

Learn more about why John Martin was awarded runner up in this year’s competition.

John farms 300 acres in Dorset on an all arable rotation with two thirds of the farm in spring cropping. The farm was a former dairy farm until 2000, and since then the overarching aim of the management has been to keep the soil status in good health. John’s farm is situated in an area with a high degree of designations on it, being within a Class 1 Soil Protection Zone, an NVZ and the Poole Harbour Catchment, meaning that there has been a large focus on efficient nutrient use, especially on nitrogen.

A key strategy employed on the farm to boost soil health and also to help capture nutrients has been the use of cover cropping. All of the land that is in spring crops has a cover crop before it, and John has been experimenting with increasing the diversity of the mix. The mix now includes sunflowers, buckwheat, phacelia, linseed, and various clovers to ensure that the soil biology have a diverse diet.

John explains:

It’s like taking a coach party of people to a fish and chip shop, some will want fish, some sausage and some pie and chips. All of the soil bugs bring something to the party and are all important, so we need to provide a diverse food supply for them so they can do their jobs.”  Nothing is set in stone however and everything is flexible. The farm grows a high proportion of spring cropping, which allows the cover crops to be utilised fully. John explains “We harvest sunshine for 6 months of the year to feed the combine (and the bank manager), we can spend the other 6 months feeding the soil.

The diversity of cover crops grown provide lots of roots to feed the soil microbes and rapid breakdown of Nitrogen release for the spring.  

The group then moved onto look at some flower strips which John has planted in one of his fields through the ASSIST project. The overarching aim of these was to encourage biodiversity into the fields rather than just being round the edges, and also to allow the farmer to move away from insecticides and use natural pest management. The strips are 8m wide with 2m of tussocky grasses framing the flowers in the middle. John is seeing the benefits of these strips, but is learning as the project develops.

The first year we just planted some annual strips of flowers, but it was a little bit like a drive through McDonalds; so we then replaced them with permanent strips that provide food and habitat throughout the year.

The strips were established at the end of March with a Vaderstaad Drill.  and were cut every 8 days.  John has these strips in a variety of fields and has three strips per field. Next year the plan is to cut them once or twice.

John is farming on chalk soils and enjoys the challenges that this soil type can bring. He first started looking at soils in the 80s, digging his first soil pit in 1985. This then prompted a move towards bigger, low ground pressure tyres and focussing on axle weights of machinery to minimise compaction. There is always a spade in the tractor allowing John to assess the structure of the soil at two key periods in the year; in winter when the soils are wet, to assess how the drainage is doing, and then after cultivation to see whether the machine has achieved its goal.

The chalk soils mean that John is keen to build resilience in his soils to aid water retention. A key strategy is focussing on returning organic matter to the soil to build humus. All of the crop residues are chopped and returned to the fields and 75% of the farm is cover cropped to ensure that there is something growing all year round. When John started his transition to enhanced soil management he took some baseline soil samples.

He explains

“We tested fields for organic matter and they weren’t bad, but we wanted to get another 1 – 1.5%. If we can get hold of that then we’ve got more resilient soils to do spring cropping. We can tell that we are moving in the right direction as the soils are much more springy. That elasticity is coming from the humus and the soils are developing the resilience to carry us through.”

The farm is situated in a highly protected area for water qualiy. The farm sits above a Wessex Water pumping station and as such Nitrogen is limited and cover crops are always grown. John’s next step is looking at how to cut his Nitrogen back on his spring barley and is making good progress on its reduction. “We’ve got to make more out of Nitrogen,” John explains, “which is all about looking at holding onto nutrients over the winter and then using it efficiently during the growing season.”

John has been running various trials on the farm, including one with Wessex Water looking at cover crops after peas, to try and find a way of harvesting the Nitrogen in the soil after peas. After the peas were harvested, a cover crop was drilled and when the cover crop was up and away in mid November the next crop wsas direct drilled into it. The cover crop was sprayed out in the spring. Although this approach led to a 20% yield penalty the leaching from the porous pots (which Wessex Water had installed to look at leaching rates) dropped from 67% to 4%. This trial is being run again this year with different mixes of cover crops that are established and terminated in different ways to look at the optimal method which effectively captures Nitrogen but provides a good yield.

John’s focus on his soils is linked to his overarching aims for the farm which is to develop a more sustainable way of farming with consistent yields. “You never stop learning when you are focussed on the soil” John explains, “and it’s a fascinating adventure.”

Thank you to John and his family for a brilliant walk.