This is the first in a series of articles written by Andrew Ross to get us thinking about the quality and impact of the soil at Highbridge Community Farm.

Soil with high organic carbon isn’t just a good growing medium. It can help reduce atmospheric CO2 on a worldwide basis – a win for farming and a win for the planet. So, is there more we can do to increase the organic carbon levels of the soil at HCF? 

Most of us are familiar with the broad issues of climate change:

  • An increase in atmospheric carbon dioxide (CO2) concentration from 278 ppm in the pre-Industrial period (circa 1750) to 405.5 ppm in 2017
  • An increase of the greenhouse gas, methane, from 722 ppb to 1859 ppb in the same period.
  • An increase in nitrous oxide from 270 ppb to 330 ppb in the same period. (Lal, 2019)

This has already raised global temperatures by over 1⁰C since the Industrial Revolution with dire consequences, as exemplified by the increase in frequency of extreme events throughout the world. Furthermore there is the real likelihood that we will miss the target set at the Paris Climate Conference (COP21) in 2015 of limiting global warming to 1.5⁰C. (IPCC (Intergovernmental Panel on Climate Change, 2018).

The Highbridge Community Farm ethos statement says “We have evolved from the Transition Movement and retain their founding principles – a community-led response to the pressures of fossil fuel depletion and climate change, supporting local economies and moving towards a more viable and sustainable future. Now a mutual benefit co-operative society in our own right, we work together to produce food for ourselves with minimum use of fossil fuels and chemicals. We support growing techniques that maintain the natural balance of the soil, preserve wildlife and their habitats, and encourage biodiversity.”

Over our time as a community, our aim has been to grow good organic food. We have managed the soil to obtain good crops, without ever really addressing the issue of how to improve the health, fertility and productivity of our soil in an environmentally sustainable way. Ideally, this soil should be resilient to be able to cope with whatever crop is planted in it and cope with whatever combination of weather events that is thrown at it. Probably the best measure of soil health and resilience is one with a high organic carbon content.

Farmers Weekly provides a simple chart for farmers to score the quality of their soil according to the percentage of organic carbon that it contains:

  • Less than 1% – very low
  • Less than 2% – low
  • Less than 4% – medium
  • Less than 8% – high
  • Over 8% – very high

The IPCC Climate Accord, proposed in Paris in 2015, initiated the “4 per 1000 programme“. This aims to raise Soil organic carbon in world soils to a depth of 40 cm at the annual rate of 0.4% per year. The UK signed up to this initiative and Environment Secretary Michael Gove has undertaken to deliver on this ambitious goal by supporting soil health improvements in the UK.

Natural soils in Britain once contained 30-40% more organic matter than they now contain under cultivation. Most farmed soils in southern England now have less than 2% organic matter, but in the rest of the British Isles 2-6% may be found. Once organic matter levels fall to below 2% the impact can be severe. A fall in soil organic matter of 0.5% can reduce nutrient holding capacity by 4% of even fertile soils. Growers manage the levels of soil organic matter to get acceptable plant growth, which will typically mean that organic matter levels should be 3-6%. For us it should be at least 6%, preferably 8%.

There is an added benefit of raising soil organic carbon (SOC); the potential lowering of atmospheric CO2 on a worldwide basis by raising SOC is approximately 84 ppm of CO2. This burying of SOC in the soil in the form of humus is called sequestration.

So, raising SOC at Highbridge Community Farm will be a win:win. We can play our part at HCF to produce a better, more resilient and productive soil and our efforts will benefit everyone if global CO2 levels fall!