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Soil 1 - The Failure to Understand Soil

The fifth IPCC report dated to 2013 includes a chapter that discusses biogeochemical carbon, that is, carbon that is involved in the processes in the soil, whether associated with plants, animals, fungi, and microbes, or with rocks, sediments, and ground water.

In other words, the soil and all that is in it, what it does, and how it behaves.

Scientific understanding of the organic content of soils since the late the 18th century, and so it is ill defined - there is no clear definition of what humus, or humic acids, or the process of humification, actually is. Which is a little bit shocking, since the global human population relies on the soil to grow our food, and to grow he food for the animals that provide us with food.

In palaeoecology when we examine organic sediment, like peat, or lakebed sediment, we have to process it to be able to get at the fossils, micro fossils, like pollen, spores, diatoms and so on. We can get rid of humus, in the form of humic acid and fulvic acid, by cancelling them out chemically with an alkali, sodium hydroxide or potassium hydroxide, and the humin fraction, the left over dark brown solid organic material that we don't want, then has to be dissolved using an oxidising agent, like a strong acid. That's about as close as we get to humus.

Humus, as an organic product, is essential for radiocarbon dating of sediments. Although we are now learning that humus is a constantly changing and dynamic set of chemicals, containing a lot of carbon, the original carbon held within these chemicals remains the same, for the purposes of dating, even though the compounds they are part of change. So radiocarbon dating is still valid, even though our understanding of humus is changing.

And it desperately needs to change.

We are told that it is essential to increase the humus content of the soil, beyond knowing that this means adding in organic matter that is in a process of active aerobic decomposition, it is not possible to define exactly what humus is, chemically. But your farm advisor, unless you are an organic farmer, won't advise increasing humus content of the soil, for one very good reason. The original concept of humus, how it forms - the process of humification - and what happens to it, defined it as a substance derived from organic matter that is a dark brown colour and remains in the soil. So on that basis there is clearly no point in adding more, and that is why the agricultural industry applies fertiliser, to add to the beneficial effect of the existing humus.

Except humus does not persist in the soil.

This of course is of great importance to all of us. The fertility of the soil is what grows our food, and although it all seems to have been working fine up to now, the failure to add organic matter to the soil is having several long term, global effects. So much so that the United Nations is concerned over the increasing Fertility Crisis that is creeping across the globe. See the report here. The decline of soil organic matter is the second most concerning threat to soil biodiversity; the first is human intensive exploitation. The organic matter in the soil is not just a chemical hotch-potch that helps crops grow, it is a complex mixture of organic materials at various stages of decomposition, and also mineral matter, which is part of a complex interaction between the microbes and organisms in the soil, the water in the ground, the gases in the air, the plants that grow, die, and decay, fungi, worms, bacteria... Global Soil Biodiversity Initiative. In fact the mass of microbial organisms in an acre of good topsoil is equivalent to the mass of two cows. For every acre. All year round. That is somewhere between 2 and 3 tonnes of microbes per acre. (If that seems hard to conceive, then just consider that every time 1 mm of rain falls on 1 acre, that is about 1/2 tonne of water falling from out of the sky.).

And so we come back to biodiversity and the benefits of a healthy soil. A soil with a thriving and diverse population of organisms has structure. It has drainage and aeration channels. It has roots of plants, rhizobia of fungi, burrows of worms and insects. Drainage is aided because of the many pathways into the soil that the water can take. Water retenetion is greater because of the many gaps and holes and inter particle gaps where it can reside. (Although those two statements appear contradictory, they are actually a good example of how the natural world creates systems that serve several, sometimes opposing, functions at the same time - see Ben-Noah, I. (2023), Air flow dynamics in wet soils: challenges and knowledge gaps, Eos, 104, . Published on 6 July 2023.). Stability of the soil against erosion is greater because of the organic molecules and ill defined substances that stick soil particles together, and the extensive root systems of healthy plants that bind the topsoil. And we can learn a lot about the benefits of these properties of a healthy high organic matter soil by looking at the environment when West Cork was forming.

About 380 million years ago the sediment that is now the bedrock in West Cork was being deposited in a vast sandy, muddy, silty, subsiding basin in a dry and sometimes arid and hot plain, between mountains to the north and the coast to the south. There were few plants, and those that there were, were small, rootless, stemless and leafless - they were like mosses and liverworts that we see today. And the amount of erosion and flooding that went on was enormous - West Cork lies over a sedimentary basin where over 6 km depth of sediment was deposited, the land surface sinking as the sediment washed in. Periodic floods saturated the land surface, swept in vast loads of sediment, silt and sand, and then it all slowly soaked away or dried out in the hot sun. Carbon dioxide levels were considerably higher than now. And this was all because there were no plants.

There was also no soil.