• Philip

Carbon complexity

There has never been any doubt in my mind that the application of organic manure to the soil is of paramount importance to “modern conventional, commercial agriculture that relies on chemical intervention to fight pests and provide plant nutrition.” Where-as our organic farming colleagues “rely on natural principles like biodiversity and composting to produce healthy, abundant food (1).”

I am a BASIS qualified Agronomist and belong to the Professional Register but I also belong to other interesting and informative groups one of which is called the “The Big Compost Experiment.” So, when recently asked if buying compost was a good commercial decision or not, my initial reaction was NO it is not. The next question - Why did I say that?

It is a fact that the quality of compost varies widely and by that, I mean it can contain non-organic material such as plastic. If the material has not been sufficiently processed it may also contain pathogens which, when introduced to the farm create problems for an indefinable length of time. So, spending money to increase the amount of risk associated with growing a crop is not, in my opinion, a good starting position. Initially it may be better to look more closely at what we are doing on farm before spending cash.

One of the most important sources of organic residues are the current crops themselves. Stubble, aftermath and especially root residues left in the soil to decay make up a large bulk of contributions. Few realise how much residual root systems aid in the conditioning of their soil. Without these residues the practical maintenance of soil humus in most cases would be impossible.

With this thought in mind, it is worth remembering that going for optimum yield usually means an increase in the number of roots remaining after harvest. It also means more crop residues to return to the soil, so rather than sell the straw to someone else and buy in troubles, how about simply leaving it in situ?

Much is talked about the environment, carbon and of a biodiversity of soils however little is understood by the public, politicians or environmentalists about the subject. It is a fact that we are talking about millions of tonnes of soil, millions of tonnes of lifeforms and million upon millions of tonnes of plant material. Factor in the influence of climate, variability in parent material and position upon the globe and I do not see how any one person, scientist or not, can accurately, reliably and honestly say what is precisely going on.

Much is talked about carbon but the reality is that if we are interested in the health of our soil then what we are really concerned about is that much forgotten item humus.

So, what is humus? There is a long description of what it is and how it is formed but at this time suffice to say it is the end material of the decomposition process. It is this which arguably has the greatest medium and long-term effect upon the quality of our soils.

The rate at which carbon is lost from the soil rapidly increases as the organic content is raised. The maintenance of humus at high levels is expensive and difficult. It is therefore unwise to hold the organic matter above a level consistent with expectant crop yields that offer optimal financial return. Just what this level should be depends on the climate, soil conditions and the particular crop grown along with the rotation and ...

(1) Manure Management on Organic Farms

.. a valuable resource for organic and sustainable soil management. … used in combination with other sustainable and organic farming practices such as crop rotation, cover cropping, green manuring, and liming… commonly applied to the field as raw manure (fresh or dried). … great for enhancing the physical condition of soil while building soil organic matter that serves as a slow-release reservoir of plant nutrients including nitrogen, phosphorus, potassium, and micronutrients.