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Getting to grips with Carbon: Written by Graham Shepherd of BioAgriNomics

Getting to grips with Carbon: Written by Graham Shepherd of BioAgriNomics
Healthy Soil
From soil carbon to carbon sequestration and carbon credits, carbon is an area of agriculture that farmers need to understand but can sometimes create confusion.

Soil carbon can be considered the holy grail of the farm and is often overlooked for the role it plays in improving production, economic and environmental performance. But what is soil carbon? Soil carbon is a measurable component of soil organic matter. Organic matter makes up just 2–10% of most soil’s mass and has an important role to play in the physical, chemical, and biological function of agricultural soils. 

The Role of Soil Carbon

Carbon, along with hydrogen and oxygen, is the basis for all life. Soil carbon or soil organic carbon is the major part of soil organic matter. Soil organic matter is made up of micro-organisms and decomposing plant and animal material.

Soil that is rich in carbon has many benefits for dairy farmers including the following: 

  •  Provides the building blocks and is a food source for the cell material of all organisms living in the soil. It promotes dry matter production.  
  • Is an important source and major reservoir of plant nutrients. A decline in soil carbon reduces the fertility and nutrient-supplying potential of soil.  
  • Plays a key role in maintaining the pH of soil including helping to buffer the build-up of heavy metals such as Cd, Pb, and As. 
  • Regulates most biological, chemical, and physical processes in soil which collectively determine soil health.  
  • Helps develop and stabilise soil structure.  
  • Cushions the impact of wheel traffic and stock treading increasing the resistance and resilience of the soil to structural degradation.  
  • Promotes filtration, movement, and retention of water.  
  • Reduces the potential for wind and water erosion.  
  • Indicates whether the soil is functioning as a carbon ‘sink’ or storage facility (sequestering carbon from the atmosphere) or as a source of greenhouse gases 

Carbon Sequestration & Carbon Credits – Getting paid to improve the environment: 

We have all heard the term carbon sequestration but there is a lot of misunderstanding around what this means and how Farmers can use it to improve their businesses – and make money.  

Soil carbon sequestration is the process in which CO2 is removed from the atmosphere and stored in the soil carbon pool. The draw-down of atmospheric C is only one way to sequester soil C. This process is primarily mediated by plants through photosynthesis, with carbon stored in the form of soil carbon. 

Sequestering sufficient carbon can completely offset all environmental emissions, not just agricultural emissions. The sequestration of carbon can have a significant beneficial impact on climate change.  

This is where carbon credits come into play. Carbon credits are an attempt to mitigate the growth in concentrations of greenhouse gases. Carbon credits can be sold as a means of lowering the carbon footprint of a farming enterprise. By putting a price on greenhouse gases, the Emissions Trading Scheme encourages landowners to establish and manage farms in a way that increases carbon storage.  

One carbon credit is equal to one tonne of carbon dioxide, or in some markets, carbon dioxide equivalent gases. If farms in NZ sequestered 0.7 to 7 tonnes of C/ha/yr, this would be equivalent to roughly 2.6-25.7 tonnes of CO2/ ha/yr or 2.6 to 25.7 carbon credits.  

Carbon credits traded at NZD$33.55 as at the 23rd July 2020. At a minimum of $87.23/ha/ yr and a maximum of $862.20/ha/yr you can quickly see that sequestering carbon into the soil has a significant financial payoff as well as an environmental payoff.  

Farmers showing good quantitative evidence of sequestering soil carbon should be able to apply for carbon credits rather than being charged a carbon tax. While sequestering a significant amount of soil carbon over much of the area of the farm can mean a significant financial return, the real benefit of sequestering carbon in the soil comes from all the advantages of building soil carbon mentioned above. 

There is a perception that our soils are already carbon rich and it is difficult to increase the amount of carbon further. This perception is quite wrong. Our soils have on average just over 5% total organic carbon which is not high. Remembering the benefits of increased soil carbon outlined above, increasing soil carbon is an important environmental function that can also be financially rewarding. 

8 ways to increase Soil Carbon on your farm:

Dairy farmers, and farmers in general, can increase the amount of carbon in the soil by: 

  1. Increasing the amount of dry matter produced: Fifteen tonnes of DM/ha/yr produces about 9.8t C/ha/yr. Ten tonnes DM/ ha/yr produces about 6.5t C/ha/yr. Growing more grass through improved soil health by ensuring good aeration, drainage, soil fertility and biological properties and promoting the drought resistance of the soil and the wateruse efficiency of the plant will increase DM production and carbon storage.  
  2. Ensuring good soil biological properties: This includes earthworm numbers and the biomass and activity of the micro-life. Applying biological activators, or biostimulants, in a Tow and Fert, and ensuring good soil aeration, grazing management, soil moisture, food supply, soil fertility (with a pH of around 6.4), and limiting chemical sprays ensures good biological activity including that of mycorrhizal fungi 
  3. Maintaining good pasture residual levels promotes dry matter production (grass grows grass) and therefore the production of carbon. This means avoiding over-grazing which reduces the length and density of the root system making pastures susceptible to stress.  
  4. Developing the length and density of the root system: Farmers can do this by sowing deep rooting pasture species and cover crops, whilst avoiding over-grazing. This will help ensure the sequestration of soil carbon in the lower sub-soil between 400-1000mm. 
  5. Maintaining good soil structure: Good soil structure is soft and crumbly with good aggregation and allows the ready growth and extension of the root system resulting in the input of soil carbon. Feeding the soil biology (your bio-engineers), promoting a good root system and avoiding severe treading damage and over cultivation will help promote good soil structure.  
  6. Minimising soil disturbance: Soil carbon volatises into the atmosphere when the soil is cultivated. Avoid or minimise the use of a mouldboard plough, for example. 
  7.  Ensuring good soil fertility: Encourage a good microbial biomass and activity, good soil aeration, and where possible, the addition of nutrients should include foliar spray applications to raise soil fertility. (The advantages and benefits of a foliar application are well documented in the scientific literature, some of which are covered in Volumes 2 & 3 of the Tow and Fert Tabloids.)  
  8. Applying carbon farming techniques that draw-down the CO2 in the atmosphere, converting it to dissolved organic C in the soil. In addition to the 7 mechanisms mentioned above, these draw-down techniques include:  
    • a. Promoting the photosynthetic capacity of plants, i.e. the amount of pasture cover, cover-crops etc. grown throughout the year. This increases the ‘solar panels’ available to capture and convert the CO2 and H2O in the atmosphere to sugars (dissolved organic carbon) and oxygen through the process of photosynthesis.  
    • b. Promoting the photosynthetic rate of the plants, i.e. the ability of plants to increase the rate of photosynthesis and therefore the production of carbon by having good soil fertility, good soil structure, aeration and soil moisture levels, and good microbial biomass, diversity and activity.
A comparison image highlighting the difference in root systems across different lengths of grass.

The shorter the foliage above ground, the shorter the root structure which can lead to low soil carbon levels and problems such as compaction, runoff, leaching and poor soil health. Farmers need to think about ‘growing roots’, and in so doing increasing soil carbon, to grow more grass.

The significance of the above mechanisms is not as widely appreciated as they should be. This may be due to vested interests and the lack of awareness of how our common management practices reduce the activity of the key microbes involved in the sequestration of soil carbon. 

Article written by Graham Shepherd  of BioAgriNomics
[email protected]  
P. 021 51 5703 | 

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