Soil Carbon Sequestration

Background

Soil and Climate Change

Rising level of carbon dioxide in the air and worsening climate change are well recognised facts now. Apparently burning fossil fuels is the main reason but soil is actually another significant source of carbon emissions. Changing forests into agricultural lands, and misusing the lands by excessive tillage, fertilization as well as pesticide applications both speed up the oxidation of the carbon stored in soil, resulting in significant carbon emissions. Therefore, apart from reducing the use of fossil fuels, letting the carbon in the atmosphere go back to soil is also important.

The earth has 5 natural carbon pools, namely (ranging from the highest carbon storage to lowest): oceans, fossil, soil, atmosphere and terrestrial biomass. It is surprising that soil itself holds more carbon than the atmosphere and terrestrial biomass added together. Over half of the soil carbon is in organic form.[1] Though massive soil carbon has been lost to the air in the past, soil could also be seen as a huge potential to take back the carbon, as long as the soil is taken care of in the right way.

Organic carbon in soil not only balance the amount of carbon in the air, it is also the foundation of all the functions that soil performs. Sufficient soil organic carbon ensures high quality of crops, high productivity, rich farmland biodiversity, high water and nutrient retention, reduced soil erosion, etcl. These are crucial to all lives including us.

There has been many initiatives and actions internationally that promote soil carbon sequestration. Food and Agriculture Organization of the United Nations (FAO) proposed “climate-smart agriculture” in 2013 to highlight the connections between agriculture and climate, and 2015 was designated as the International Year of Soil to further raise the awareness on soil; French government also announced the commencement of “4 per 1000” Initiative in Paris COP21, suggesting all farmlands increase their organic carbon content at 0.4% annually, which is now gaining momentum with growing support from different countries and organizations. Soil carbon sequestration is actionable now and here, not another false promise regarding the big climate issue.


  1. Nature Education on soil carbon storage: https://www.nature.com/scitable/knowledge/library/soil-carbon-storage-84223790/#

Regenerative Farming

Definition by Regeneration International on 16 February 2017:

It describes farming and grazing practices that, among other benefits, reverse climate change by rebuilding soil organic matter and restoring degraded soil biodiversity – resulting in both carbon drawdown and improving the water cycle.[1]

(Remark: This definition will continue to evolve as research and practice emerge and reveal what the health of soils is, and how to sequester carbon and build topsoil.)

Regenerative farming goes beyond organic or sustainable. It not only stresses on “not harming the land” but also enhancing its productivity by understanding, respecting and mimicking the mechanisms of nature on farmland. Nowadays, agriculture, without doubt an artificial system, has developed a generally accepted but flawed paradigm to control and monitor the nature, rather than understanding the deep-rooted causes of different undesirable symptoms we observe in the field.

To be more concrete, regenerative farming means
(i) restoring carbon back to soil through the most important natural process: photosynthesis, and
(ii) enriching soil life in terms of diversity and quantity

It is a win-win-win situation where farmers harvest more good food, consumers enjoy safe tasty food full of nutrients and there is a good chance that we reverse climate change by storing and stabilizing carbon in the soil. With healthy soil, farmers can grow plants in a stress-free environment without synthetic chemicals that poison the food and degrade the soil, in return, plants thrive and produce good harvest of high-quality nutrient-dense food.

Here is a well-written overview by Jack Kittredge that we highly recommend to everyone who has the will to take a regenerative step in agriculture:

Soil Carbon Restoration: Can Biology do the Job?

Practices towards regenerative soil

If you are a farmer, or you have practical experiences of farming, you may wonder how to farm or manage your garden towards a regenerative direction. Here we raise some of the practices that we think are the most crucial to start with. Please be reminded that this is not intended to be an exhausted list and we definitely have to adjust according to farm scale, local resources, weather and climate differences, etc.:

  • Start composting: Make sure the compost is in good condition- thermal and aerated. Scroll down to see the introductory video by Kiss the Ground, “the Compost Story”.
  • No-till/ minimum tillage: Tillage is one of the most soil-degrading practices that break soil aggregation and fungal hyphae, while intensifying the decomposition of soil organic carbon. It is also a major cause of soil compaction.
  • Cover crops: Choose different locally available species of legumes and deep-rooted grass, cut and mow them before flowering to increase soil carbon.  Here is a good article to understand the mechanism of cover crops.
  • Keep the soil covered: Plants act as a barrier between air and soil, protecting soil from erosion by wind and water. Most importantly, plants feed carbon to soil through photosynthesis, and they are the “caretaker” of soil. [2]
  • Plant perennials: Most of our cash crops in Hong Kong are annuals. However, perennials with deep root systems build soil structure with minimal soil disturbance and retain nutrients.[3]
  • Intercropping and crop rotation: Plant diverse plants! One of the keys to support the soil microbial life is to promote crop diversity. In nature, the higher the biodiversity in a system, the healthier and more resilient the ecosystem is. [4]

 

References:

[1] Regenerative International: http://regenerationinternational.org/why-regenerative-agriculture/

[2] Andersen, A. B. (2000). Science in agriculture: Advanced methods for sustainable farming. Acres U.S.A.

[3] Green America: https://www.greenamerica.org/blog/methods-regenerative-agriculture-1

[4] Soil Carbon Restoration: Can Biology do the Job?, Retrieved from: http://www.nofamass.org/sites/default/files/2015_White_Paper_web.pdf