Soil Carbon and Organic Matter - What’s the big deal

There is an increasing amount of interest being generated in agriculture at the moment with regards to soil carbon and how farmers and land managers can increase the levels of Organic matter in our soils.

Soil carbon is not technically a plant nutrient, although it is present in every living organism, including plants, therefore it is a vital ingredient. The process of photosynthesis is the key process involved in the production of carbon. In this process, Carbon dioxide and water are converted into a range of plant materials. This process occurs in the green parts of plants and requires light energy from sunlight.  The products of this process are Sugars and Oxygen. The sugar component is rich in carbon, and the oxygen is released from the plants and this vital for animals and people to breathe.

Many people will recognize that a great source of carbon is contained in the plant material such as roots, stems and leaves. These can all be mulched and or grazed and returned back to the soil as clippings, dung etc.

When we cut and or remove products like hay, silage, grain and meat we are removing a great deal of carbon from that local system and taking it somewhere else. As farmers we have to do this as selling meat or plant products is how we ultimately make money.

However, an often poorly understood source of carbon is in the form of root exudates. These exudates are Carbon rich substances that are given off from the roots of living green plants. These exudates include sugar, amino acids, hormones and enzymes. “Around half of the carbon fixed by photosynthesis is exported to the roots” DPI NSW - Key soil carbon messages -Climate in Primary Industries Unit, Agricultural Resources Branch  

These root exudates can be used to fuel the soil microbiology. The really cool bit is that if farmers can focus on building carbon in the soil by having a diverse range of living roots in the soil at all times, they will build exponentially the microbial population.

Dr Christine Jones - 2007 (Soil Carbon means water to me) states that “for every 1% increase in the level of soil organic carbon will enable us to store approximately 144,000 litres (15,400 U.S. gallons), or about 16,000 extra buckets of water per hectare, in addition to the existing water-holding capacity of the soil itself.”

We need to remember that as well as the exudates being carbon rich, the resulting increase in soil microbes will add to the level of soil carbon as they are also composed of around 50% carbon. 

Increasing soil carbon helps our farms, our environment and potentially our balance sheet

Increasing soil carbon helps our farms, our environment and potentially our balance sheet, How?

If we increase soil carbon;

• We can increase the volume of water being stored (Water holding capacity) in our soil, we can also increase the effectiveness of rainfall events by ensuring more of that rainfall doesn’t run or evaporate off.

• We can increase our soil cation exchange capacity, therefore allowing nutrients to be held in the soil at greater rates. These may otherwise leach away.

• We Increase the water infiltration rates of the soils as carbon will help our soils become more like a sponge.

• ·We will make our soils softer and less compacted. This will allow plant roots to travel more easily through the soil and should make our soils less affected if they do get compacted.

More water and softer more reactive soil can only lead to greater productivity. That doesn’t always mean yield, It may mean that we spend less to get the same result.

How can we do it;

There are a number of ways to lift the soil carbon levels of our soil

1.       Buy it or import it to the farm from somewhere – eg Chicken litter, compost, cow manure, feedlot waste etc.

Ultimately this will cost money for freight, spreading, labour as well as losses.

2.       Increase the density of living plants – The greater number of living plants per square metre per unit of time, the greater the ability to capture carbon through photosynthesis. Remember that bare soil and chemically fallowed ground will have zero photosynthetic ability.

3.       Increase plant species diversity – Different plants grow at different times, so while one is dormant, another will be actively growing. Their roots systems have different lengths as well, so root exudates will be delivered to different levels of the soil. They also grow at different heights and have different leaf structures which will allow them to capture more light for photosynthesis. Aiming to grow as many varieties of perennial plants as possible is the key

4.       Utilise animals – Cattle, sheep, poultry and pigs can all have a role in cycling carbon. Judicious and controlled grazing regimes such as cell grazing where animals are continuously moved will help cycle the plant material and the urine and dung will help stimulate the soil microbial population.

Which practices are detrimental to soil carbon levels.

There are a number of practices that negatively affect soil carbon levels.

1.       Loss of perennial groundcover. No plants = No photosynthesis.

2.       Intensive cultivation. Excessive tillage accelerates soil carbon decomposition

3.       Bare fallow, ploughing the soil and leaving it bare, zero living roots in the soil. No plants = no photosynthesis.

4.       Burning crop residue and pasture. Not only will burning stop plants from photosynthesizing, lots of carbon will be released into the atmosphere and transported to a new location.

5.       Continuous grazing. This will cause perennial plants to remain short. Root growth is proportional to shoot growth, therefore it stands to reason that continuously grazing will reduce the size of the roots system and weaken the plants.

The take home message seems to be pretty simple when you break it down.

Photosynthesis cannot occur unless plants are living and growing. Farmers and land managers should be trying to harness this continuous free service that nature has provided. If we can increase the level of soil carbon in the soils on our farms we can infiltrate and store more water. This makes every rain event more effective as we are storing greater amounts of water. We will also be optimising the storage of important soil nutrients as our soils are more reactive as they will have more carbon contained with them.  We should therefore require less fertiliser and our plants will hang on much better in dry times when rainfall is scarce.  Storing more water in the soil should also help lower the temperature which should lower water evaporation from the soil surface. In our regenerative focused agriculture courses, we focus on these and many other principals. Learn how you can be part of the solution by getting in contact with us through the website.