Adding Soil Carbon, via Organic Matter, to Soil Improves Drought and Flood Resilience, Crop Yields And the ClimateDue To Carbon Increase, As Research At Rothamsted Research Demonstrates.

  Research at the world famous Rothamsted Research station in Hertfordshire has clearly demonstrated the value of adding organic matter, (compost, farmyard manure, spent mushroom compost etc) to soils. The research is based on 50 years of soil carbon data from the research station’s fields near Harpenden.   The research compared fields that have not been ploughed or cultivated for more than 50 years with traditional methods. Traditional practices decrease soil carbon which leads to a loss of soil structure, reduces the micro habitat within the soil and reduces the number and genetic variation of the bacteria, fungi and other microbiotic life within the soil.   Where organic matter is high there is relatively low level of available nitrogen. This limits microbial ability to utilise soil carbon and carbon compounds. In these situations the microbes excrete polymers that glue the soil particles together and improve soil porosity and structure. This allows water and air permeation and improves nutrient circulation.
Soil Carbon & Soil Bacteria Are Linked
Soil Carbon & Soil Bacteria Are Linked
  The soil structure needs to be porous if plant life is to be healthy. Soil pore space is however very small. It’s normally smaller than the diameter of a human hair. To maintain this structure the microbes need to excrete the polymers or the soil will “slump”. This then results in diminished soil pore space, poor aeration, poor drainage and poor plant growth.  

Chemical Fertilisers Reduces Soil Carbon, Harms Soil Structure & Reduces Plant Growth

Ammoniac Nitrogen and Phosphorus based fertilisers, which first came into agricultural practice in the post Victorian era saw an increase in nitrogen availability. Though thought important for plant growth it has led to soil microbes metabolising more nitrogen, hence excreting fewer polymers and hence altering soil structure.   In the post Victorian period, as artificial fertilisers increased in use, soil pore space decreased. Where carbon levels are low researchers have noticed that soil pores are reduced in size and poor growth results.  
Heavy cultivations destroy soil structure, damage soil carbon potential and create dust.
Heavy cultivations destroy soil structure, damage soil carbon potential and create dust.
It doesn’t end there. Because low carbon soils are deficient in air and hence oxygen, the microbes adopt a different life style and obtain their energy from nitrogen and sulphur compounds. This is an inefficient process and results in emissions of greenhouse gases, such as nitrous oxide, from the soil.   Hence the use of organic manures such as garden compost and farmyard manures decrease greenhouse gases and leads to superior plant growth.   And decreasing soil disturbance, especially due to ploughing and related cultivation techniques, also helps. This is why farmers , where possible, need to use minimal cultivation techniques and use farmyard manure in preference to manufactured chemical fertilisers. Its also part of the reason I prefer No Dig. It’s better for the soil and for the planet.

Soil Carbon & the Web Wide Network

Another reason to encourage the use of organic manures and No Dig or minimal cultivation is that organic matter encourages soil fungi and by reducing soil disturbance the soil fungi is harmed less by heavy machinery or even spades, forks and hoes. The presence of the web wide network is now proven and maintaining it in good condition significantly helps the planet and the plants in our gardens.  

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4 thoughts on “Soil Carbon, Organic Matter & Nitrogen Balance

  1. Mike says:

    Hi Stefan Thanks for another great article.
    My question is this; Wouldn’t leaving a field fallow as in the Norfolk 4year rotation plan help to restore the balance you describe above.However I am sure you have said on another article that with modern knowledge rotation is not as necessary.Please forgive me if I have misquoted you.
    I think Charles Downing also says rotation is not necessary.
    I practice a three year rotation- potatoes legumes brassicas and fit in other crops where I can as I believe this helps mother nature keep a balance and helps to reduce disease.
    Look forward to your comments about this.

    1. Stefan Drew says:

      Hi Michael

      The Norfolk four course rotation improved yields centuries ago as the type of farming practiced depleted the soil of nutrients. Before that crops were grown, taken away and no goodness returned to the soil. The Norfolk practice was different. It included livestock.

      And we would be better thinking of this form of farming as mixed farmer rather than an arable rotation as it included livestock at two stages. These were when the turnips were grown (most were grazed by sheep and is why wool became so important during this time) and during the clover and/or grass was grown. The clover added nitrogen and could have been supplemented by any legume. It was followed by wheat, another grass family crop that benefits from the nitrogen and produces higher yields the more nitrogen there is.

      Plus the clover was grazed and meant sheep droppings were added during that time.

      So the reality is that the Norfolk four course rotation was a grass family based rotation that favoured sheep (and other grazing livestock) as much as anything else. It meant a lot of carbon went back into the system and fertility maintained that way.

      When fallow periods were added to a rotation don’t for a minute think it meant nothing happened in the field. It’s highly likely that the field would have been grazed during that time.

      As for the necessity of rotations, I agree with Charles Dowding, they aren’t. Charles has experimentally grown potatoes on the same site for 7-8 years with no disease problem or decrease in yield. I’m not suggesting we should all do the same, but it proves the assumed need for rotation is largely unfounded today. Having said that, if disease or pest is prevalent in the crop then it is wise to consider it and perhaps rotate on that occasion.

      1. Mike says:

        Thanks for your detailed reply

    2. Stefan Drew says:

      I’m happy to answer further questions in comments.

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