Catching Carbon – The Mechanics of Humus Building

The introduction of carbon credits for sequestering carbon into the soils is now on the political agenda. This may well herald a golden era for agriculture. Scientists and politicians are slowly realising that there is simply no alternative but to reward and motivate farmers to undertake this urgent task. If the entire world were to immediately reduce carbon emissions by 100%, then in 200 years time we would have reduced atmospheric CO2 to the levels found in our atmosphere in 1975, which is still too high! We are, in effect, locked into self-destruct mode but there is an escape.

The saviour is humus. Carbon credits are already available for tree planting but in actual fact the soil offers a better investment. Carbon remains in biomass for an average of 10 years but it can be stored in the soil for 35 years. The Americans raise the hackles of the developing world with their greenhouse vandalism. 300 million people (just 5% of the planet’s population) generate 8 billion of the 30 billion tonnes of CO2 we spew into the atmosphere each year (over 25%) and this is obviously unfair. However, if we were to build organic matter by just 1% in US agricultural soils we would remove 4.5 billion tonnes of the offending gas from the atmosphere, representing a 50% offset of their emissions.

The Ultimate Win/Win

Humus is the single most important determinant of success in high production agriculture. It seems a remarkable stroke of luck that we are destined to be paid to increase our profitability via payment for sequestration of soil carbon.

Several years back the National Bank researched the reason for so many failed loans in the rural sector. In a study involving several hundred properties in the Hillston region of NSW, they were seeking to determine the key criteria for financial success when embarking on a new venture. Researchers found that soil carbon was the key to business success and they went as far as to link levels of organic matter to farm value. If one property featured soils with 1.4% organic matter and another had soils averaging 1.6%, then that extra 0.2% increased land value accordingly and it was suggested that future loans should be evaluated on the basis of carbon based productive potential.

The benefits of organic matter are manyfold. Water is an increasingly scarce resource and it is so much more effective to store water in humus (which holds its own weight in moisture) than in dams where evaporation is massive and there is a significant carbon footprint in delivering the water to the crop.

Good humus levels are the manifestation of a healthy microbial workforce. In the ultimate example of “give and you shall receive”, the plant produces glucose via photosynthesis and gives away 30% of its total production to the army surrounding the roots. It is these invisible workers who fix nitrogen from the atmosphere, solubilise locked up phosphate in our soils and protect the crop from disease. These creatures deliver minerals to the plant and they exude an ongoing supply of plant growth hormones in return for the sugars the plant roots provide them.

Building Humus

The Rodale Institute in the US have researched carbon-building for the past 20 years. They have shown that a combination of minimum-till, compost and cover crops can steadily build soil carbon. They are behind the suggestion that there should be a payment of US$250 per hectare for every 0.15% increase in organic matter. I believe that there are two other key humus building strategies and they include the use of microbial inoculums and the utilisation of humates.

Soil-life analysis around the globe reveals that most soils are lacking cellulose digesting fungi and these are some of the creatures responsible for creating the stable, long term carbon that is so desperately required. It is so ridiculously simple and inexpensive to “brew” these creatures and reintroduce them to the soil.

Similarly we have seen remarkable results with the use of humates to trigger humus building. Raw humates, in the form of particular types of brown coal, applied at 500 kg per hectare can serve as a powerhouse stimulant. Similarly, soluble humic acid granules applied at rates ranging from just 5 kg to 20 kg per hectare also offer a potent humus-building response.

The chief reason for the effectiveness of humic acid, in this context, relates to the fact that it is such an amazing food for cellulose-digesting fungi. However, humates impact every aspect of carbon catching, including the improvement of soil structure (for gas exchange), enhanced mineral delivery to the plant (for enhanced photosynthesis), increased moisture retention and the buffering of salt fertilisers that compromise the carbon builders.

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