Soil carbon: how it builds fertile ground for opportunities on farm

Carbon is a major component of soil organic matter yet it often goes unnoticed in farming. Meanwhile, managing nutrients like N:P:K (nitrogen, phosphorus, potassium) and other micronutrients for crop production is standard agriculture knowledge.

Recently, the rise of regenerative agriculture shed light on the importance of soil carbon for farming. Turns out, soil carbon is a major contributor not just to overall soil health and crop production but with wider effects on agriculture and climate change adaptation and mitigation.

The importance of healthy soils cannot be emphasised enough in producing yields and healthy crops. Therefore, to maintain soil health for the long term, farm management needs to adopt practices that promote soil fertility.

Farmers turning to soil carbon in building fertile lands must know first, what exactly is soil carbon? And what opportunities does it bring to farms?

What is soil carbon?

Soil is only ever really soil when it’s teeming with organic components. Otherwise, it’s just dirt. And when you look at dirt and fertile soil in comparison, the rich colour of healthy soils is a basic indicator of health.

What imparts this darker hue is the organic matter in the soils. Soil organic matter is derived from decomposing and already decomposed plant and animal material, as well as excretions and soil microbes, that form a reliable mixture with soil. When soil is rich in organic matter, it also holds nutrients like nitrogen, phosphorus, and carbon.

Soil carbon (or soil organic carbon) is the fraction of the element carbon found in soil organic matter. It is the most abundant element and is estimated that the carbon content in organic soil matter is about 58%.

Carbon impacts the chemical, physical, and biological properties of the soil. And because soils store large amounts of carbon, this ecosystem service is seen as one of the ways to limit global warming. Turning the soil’s natural capacity to hold carbon through soil carbon sequestration.

What is soil carbon sequestration?

Soil carbon sequestration harnesses the capacity of soils to absorb and store carbon as a way to limit the increasing CO2 concentrations in the atmosphere. Soil carbon sequestration comes in many forms and techniques.

In agriculture, soil carbon storage can also be referred to as carbon farming or regenerative agriculture.

Globally, soils are the largest carbon reservoirs, and agricultural soils have the potential to sequester more carbon. In the European Union, one estimate suggests that soil carbon storage in croplands has the potential to hold up to 90–120 Mt C per year.

Sequestering carbon from the atmosphere into agricultural lands is a climate mitigation strategy that has direct impacts on farm productivity. Carbon is a crucial component that makes up healthy soils. And the impacts of healthy soils on a farmer translate to yield improvements, long-term farm productivity, and increased profitability potential.

Why is soil carbon important to me as a farmer?

While soil carbon is present in all agricultural lands, overall soil carbon stock and soil carbon levels have decreased due to natural processes as well as improper land management. Soils that have become less productive are often dealt with impermanent fixes in soil amendments.

But how does soil carbon benefit farming?

Farm soils rich in carbon is key to soil productivity. Carbon-rich soils contribute to good yield and long-term sustainability which can have good impacts on profit.

How does soil carbon affect soil health?

Healthy soils teem with life, soil minerals, and life-nourishing properties crucial for plants, animals, and microorganisms to flourish. With healthy soil carbon, the properties of the soil also benefit, which ultimately serves to improve a farm’s productivity.

Below are some of the ways soil carbon contributes to healthy farm soils.

Improves resilience to drought and extreme rainfall

Extreme weather such as drought is lasting longer and becoming more frequent. This makes the effects on yields harder to control and predict.

When the soil is healthy, water absorption and soil moisture retention are improved. Carbon increases the water-holding capacity. It is estimated that soil organic matter holds 3-5 times more water than mineral parts of soil,

Soils that are healthy and rich in carbon can effectively absorb rainfall as well as support crops during droughts. During wet seasons where rain is more frequent, more water can be retained in healthy soils. This feature can act as a water reservoir that plants can rely on during dry months or droughts.

Influences nutrient availability and plant uptake

This is where the life found in soils, such as small organisms and plants, become beneficial for nutrient uptake. The nutrients from decaying matter become a source of nutrition for crops and other life-forms in the soil once microbial life gets to them. In fact, nutrients like nitrogen must be broken down by microbes before plants can uptake them.

Healthy soils are rich in organic matter which releases various nutrients when broken down by microorganisms. Key nutrients such as nitrogen, phosphorus, potassium and sulfur are made available to plants due to microbial processes.

Reduces soil density

Soil compaction and density are indicators and drivers of soil health. An abundance of organic matter provides a great environment for all sorts of life to prosper in the soil. As microbes, earthworms, and other organisms move around in the soil to take in carbon as their source of energy, these create pockets of spaces that break up soil density.

Similarly, soil organic matter helps form and maintain the air passages and channels that protect the soil from compaction. Soil that is less compact and less dense encourages plant root development and penetration. The improved root system of plants indicates better nutrient and water absorption. This aids the soil’s capacity to withstand erosion and other soil disturbance. It also makes the soil more friable, less sticky, and easier to work.

Enhances soil’s capacity to host life

Soil biodiversity boosts the biological and structural functions of soil health. Plant and soil processes contribute to overall soil functioning — but equally as important are soil microorganisms. The microbial life in the soil feeds on carbon and organic matter components for energy. And in return, soil microorganisms transform organic matter into available nutrients that can then be used by the plants and the soil.

How does soil carbon benefit income?

Carbon-rich organic matter in soil is considered key to soil health. While there are many variations based on climate, the type of soil, and farm management, improving soil fertility does have a direct impact on the bottom-line goals of farmers.

• Yield stability

The quality and quantity of harvested crops depend on many factors, and soil management is only one of them. In practice, farmers and researchers alike found that soil organic carbon plays a role in improving crop yields.

One of the ways healthy soils improve yield is during unstable weather events like drought. Water-holding capacity is improved when organic matter is present in the soil. This function especially becomes more reliable during persistent droughts that impact crop production. Similarly, dis­ease resistance, seed germination, root development, and plant growth are some ways soil carbon can help with yield stability.

• Long-term productivity

Building healthy soils requires continuous commitment. Organic matter buildup in soil happens over time. This is why prioritising soil health is associated with sustainable farming practices meant to accrue carbon pools in the soil for the long term.

With climate change effects posing direct threats to crop production, ensuring the health of soils helps safeguard resilience over climate instability. Steadily restoring the health of soils over time also allows land managers to keep agricultural soils productive over the years.

Agriculture is a soil-intensive process that breaks down the carbon in the soil to cultivate crops. Carbon farming practices help maintain soil quality instead of just depleting it of its life-giving properties.

• Expands income sources

Farming that focuses on building overall soil health improves fertility while reducing the need to use synthetic fertiliser application and other heavy equipment. Less dependence on these supplies can help farmers cut back on their budget to run the farm.

Apart from cost reductions, soil carbon sequestration strategies in agriculture provide income-generating incentives through a carbon program. Carbon farming focuses on strategies to sequester carbon from the atmosphere and into agriculture and grassland soils

Carbon capture farming through carbon programs means farmers have the option to earn for effectively limiting emissions with measured and verified records that come in the form of carbon credits. These credits are sold to organisations looking to offset their carbon dioxide and other greenhouse gas emissions.

Creating carbon credits for farmers is a process that begins with an initial carbon consultation that allows historical tracking of effective carbon storage in the soil and emissions reductions.

How can I build soil carbon?

Increased carbon sequestration in farms can be achieved by adopting carbon farming practices that also benefit soil health and soil productivity. As land managers, placing the health of soils central to farm operations may not seem obvious at first. And with varying purposes, developing carbon in the soils takes years, decades, and even centuries to form (referred to as active, slow, and passive carbon pools, respectively).

Regenerative soil practice, however, is all about playing the long game — building carbon in the soil to help future-proof farms. Below are some basic examples of soil health-restoring ideas in agriculture, keeping in mind the specific practical and logistical considerations of your farm.

How to manage soils to increase soil carbon?

Minimising soil disturbance

Tillage contributes the most to soil disturbance with implications on soil erosion as it also leads to soil organic matter losses. However, tillage is used by many farmers to prepare seeds for cultivation and manage crop residue by mixing them with soil.

A best management practice that centers on soil conservation is minimising till or using no-till completely. No-till practices have been found to have 71% lower greenhouse gas intensity than conventional tillage.

Covering the soil

Soils need protection and it makes sense that soil conservation techniques such as using a cover crop and leaving straws in the fields are found beneficial by farmers. The added inputs of organic matter can minimise losses that also help the soil from eroding while improving soil structure.

Cultivating crops in rotation

Adopting crop management practices that increase carbon inputs in the soil helps with improving productivity and soil condition. Crop rotation methods such as seasonal cover crops or continuous cropping which reduces fallow frequency are some ways to boost soil organic carbon stock.

Takeaways

Soil management is crucial for long term sustainability of croplands. And soil carbon is an area with a big potential for improvement and impact. Carbon affects the health of the soil which can determine its productivity and profitability for farmers.

There are many factors that affect soil carbon like temperature, weather, soil acidity, geography, among other things. But management decisions on the farm play a big role as well.

Managing soil health is about finding the right balance in carbon input and outputs. Minimising soil disturbance, covering the soil, and cultivating crops in rotation are some ways soil can be managed that accounts for soil carbon, and ultimately soil health.

Building soil carbon gains takes time and long-term commitment is essential for healthy soils. Added incentives in carbon farming can provide short-term gains while maintaining a long-term outlook on the sustainability of farmland soil health. 

Sources

• Paustian, K., Larson, E., Kent, J., Marx, E., Swan, A. (2019). Soil C Sequestration as a Biological Negative Emission Strategy. Frontiers in Climate. Vol. 1 pp. 8. DOI: 10.3389/fclim.2019.00008. https://www.frontiersin.org/article/10.3389/fclim.2019.00008

• Haddaway, N.R., Hedlund, K., Jackson, L.E. et al. (2015). What are the effects of agricultural management on soil organic carbon in boreo-temperate systems? Environ Evid 4, 23. https://doi.org/10.1186/s13750-015-0049-0

• Smith, P. (2004). Carbon sequestration in croplands: the potential in Europe and the global context. European Journal of Agronomy, Volume 20, Issue 3, Pages 229-236, ISSN 1161-0301. https://doi.org/10.1016/j.eja.2003.08.002. https://www.sciencedirect.com/science/article/pii/S1161030103000996

• Oldfield, E. E., Bradford, M. A., Wood, S. A. (2019). Global meta-analysis of the relationship between soil organic matter and crop yields. Soil. Vol. 5, 1, pp. 15-32. DOI: 10.5194/soil-5-15-2019. https://soil.copernicus.org/articles/5/15/2019/

• Gobin, A., Campling, P., Janssen, L., Desmet, N., van Delden, H., Hurkens, J., Lavelle, P., Berman, S. (2011). Soil organic matter management across the EU – best practices, constraints and trade-offs, Final Report for the European Commission’s DG Environment, September 2011. https://ec.europa.eu/environment/soil/pdf/som/full_report.pdf