Soil Fertility, Biodiversity, and the Arc of Collapse and Recovery - Part 2

Published:May 2026

The relationship between soil fertility and biodiversity is central to understanding how ecosystems function and change over time. Across many landscapes, ecosystems move through cycles of decline and recovery, shaped by shifts in nutrients, species composition and environmental conditions.

What My Soil Test Revealed About West Cork Land, Farming, and the Hidden Cost of Fertility.

As I described in my previous blog, for years I have struggled to grow vegetables successfully on our land in West Cork. Some crops performed tolerably, others remained weak, yellowed early, or simply failed to thrive. The common assumption is often that Irish farmland is naturally fertile, but a recent laboratory soil test told a rather different story.

Maybe at this point I should issue a warning to farmers and gardeners. Beware soil test kits and pH meters. I had a pH meter, which consistently told me - for those 15 years I assumed it was right - that my soil was at a comfortable 6.5 - just slightly below neutral and pretty much optimum for gardening. But I became suspicious when my grandson was doing a project in our field for his Agscience (the relative efficacy of slurry type and application on grassland) and he tested the soil. He told me it was 5. Now, the difference between 5 and 6.5 does not sound very much, but it is. The pH scale is a logarithmic scale which means the changes between successive values represent a tenfold difference. 6 is ten times more acidic than 7, and 5 is ten times more acidic than 6. This acidity is a measure of the concentration of hydrogen ions, which in these concentrations that vary by such large amounts, play an important and highly influential role in the way chemicals of all sorts in the soil behave. These logarithmic scales are used quite a lot in the natural sciences - the values of earthquake intensity of the Richter scale, and the measures of hardness of minerals in Moh's scale. This is because of the enormous value ranges, which would be very hard to visualise on a normal linear scale, they'd literally very quickly go off the chart.

So I decided to get a soil test kit. Well, I tried another meter from the garden centre. That showed somewhere between 6.8 and 6.5 everywhere. I ordered a chemical soil test kit that would test pH, nitrogen, potash, and phosphate, from a company in Dublin. It was shipped from China. Each solution was an olive green colour, and when added to the soil solution, turned a dirty olive green colour. Even without anything in the water, it turned the same colour. That went in the bin. I bought some coloured test strips, similar to those we use in the lab, with four squares that turn different colours and allow fairly precise matching of the colours. They showed a fairly consistent range of 5.5 to 6.5 - but when I tried them with a solution of lime, they showed 7. That didn't seem right. So finally I paid for a soil test by IAS Laboratories in County Carlow and sent off my soil samples, a mix of soil from the field and the veg garden; from locations that had not been used to grow anything other than grass. It cost me €70, so I didn't want to send too many samples.

The results were revealing.

The soil proved to be distinctly acidic, with a pH of 5.5. That is ten times more acidic than the ideal of 6.5. Potassium levels were low, while magnesium was unusually high. Zinc and copper levels were also elevated. Organic matter was high, reflecting the wet Atlantic climate and long-term accumulation of humic material. Most significantly, the laboratory recommended the equivalent of over six tonnes of lime per hectare simply to bring the soil into a more suitable condition for crop growth.

These results immediately explained many of the problems experienced in the vegetable garden.

Most vegetables prefer soils closer to neutral pH, for very good reasons. In acidic conditions, nutrient uptake becomes more difficult, biological activity changes, and some nutrients become unavailable while others become excessively soluble. Potassium deficiency is particularly important. Potassium is essential for strong stems, root development, disease resistance, and overall plant vigour. In high-rainfall environments such as West Cork, potassium is continually leached from the soil profile. This process is especially severe on acidic sandstone-derived soils.

The geology of much of West Cork predisposes the land toward this condition. Unlike limestone regions, which naturally replenish calcium and buffer acidity, the Devonian and Carboniferous siliclastic rocks of the region are inherently poor in base-rich minerals. Combined with extremely high rainfall, this creates an environment where leaching dominates. Over thousands of years, rainwater removes calcium, potassium, and other soluble nutrients from the soil.

What became striking during this process was how similar this is to palaeoecology itself.

In palaeoecology we rarely observe the past directly. Instead, we infer environmental conditions from proxies — pollen, chironomids, plant macrofossils, geochemistry, sediment colour, charcoal, isotopes, and countless subtle indicators that point toward wider ecological conditions. A lake sediment core never tells us directly that temperatures fell or woodland disappeared. Rather, the evidence acts as a proxy for processes taking place within the wider environment.

Exactly the same logic applies in the vegetable garden.

Yellowing leaves, poor root development, weak stems, fungal and insect attack, stunted growth, moss expansion, dock proliferation, or crops that repeatedly fail are all ecological proxies. They are symptoms pointing toward underlying processes within the soil system — acidity, leaching, nutrient imbalance, compaction, hydrological instability, or declining biological function. Farmers and gardeners often read landscapes instinctively in precisely this way, even if they do not describe it in scientific terms.

There can be no doubt that the old ways of farming and gardening recognised these signs, and knew what they indicated, and understood what actions to take to mitigate the problems.

The soil itself is likely a Brown Podzolic soil — one of the most characteristic soil types of Atlantic western Ireland. Such soils develop naturally under conditions of high rainfall, acidic parent material, and continual leaching. They are not degraded soils in the conventional sense; rather, they represent the natural direction in which these landscapes evolve.

Before human intervention, however, the landscape functioned differently.

After the last ice age there was no soil as such. Just mounds of fluvioglacial deposits, mineral in origin, dumped and smeared by the ice and by meltwater streams. Silts, sands, gravels, and rocks. Gradually lichens and mosses took hold, lived, and died. High rainfall and slow decomposition promoted the accumulation of organic matter derived from plant biomass. These organic deposits started to hold water, and acted as places of nutrition for new plants. Within 10,000 years the soil had built up so that by the time the Holocene started at about 11 and a half thousand years ago, there was probably a substantial soil in which trees could take root and grow. The original ecology of much of West Cork was then likely a mosaic of oak and birch woodland, scrub, wet ground, heath, and rough grassland. Trees and scrub played a critical role in nutrient retention. Deep-rooted vegetation acted as a nutrient pump, drawing minerals from depth and recycling them through leaf litter and organic matter accumulation. Woodland also reduced runoff, stabilised soils, moderated hydrology, and slowed nutrient loss.

Human clearance fundamentally altered this system.

As woodland disappeared and the landscape became increasingly open, the biological mechanisms that retained and recycled nutrients weakened. Nutrients removed through grazing and cropping were no longer efficiently returned. Water moved more rapidly across and through the soil. On exposed slopes, leaching intensified. Over centuries, many nutrients were gradually washed away. They had to be replaced by addition through manuring or liming, or composting bracken, which is high in potash, or spreading wood ash, which is high in potash and reduces acidity as well.

But then the modern agricultural landscape accelerated this process further.

Traditional Irish farming landscapes were often structurally complex: small enclosed fields, hedgerows, scattered trees, scrub margins, wet corners, and mixed land use created a patchwork that slowed water movement and maintained ecological diversity. During the twentieth century, mechanisation encouraged larger fields, hedge removal, drainage, and simplified pasture systems designed for efficiency and maximum output.

Modern dairy farming in West Cork is extraordinarily productive, but much of that productivity now depends on continual external inputs. Lime counteracts acidification. Potassium replaces continual losses through leaching and silage removal. Nitrogen drives rapid grass growth. Phosphorus maintains productivity on soils that naturally tend toward nutrient depletion.

In effect, many agricultural systems now function through a constant replacement of nutrients that the landscape itself is naturally predisposed to lose.

This dependency is rarely acknowledged because the system currently works. Grass grows rapidly, silage yields remain high, and fields appear productive. Yet the underlying tendency of many West Cork soils remains exactly what my own soil test revealed: acidic, leached, potassium-poor ground slowly reverting toward its natural condition.

There is another feature of the modern West Cork landscape that is rarely discussed openly, but is now commonplace: almost every farmer owns, or has access to, a large excavator. It is increasingly common to see fields re-engineered on a substantial scale. Topsoil is stripped and mounded, drains are cut, hollows filled, bedrock exposed, wet areas levelled, and the original soil profile physically rearranged before the topsoil is spread back across the surface.

From an engineering perspective this creates smoother, drier, more manageable fields. But from a soil perspective the consequences can be profound.

A soil is not simply dirt spread over rock. It is not some nameless medium that will grow crops. It is a structured ecological, biological, and chemical system that has developed over thousands of years. Its horizons, pore spaces, fungal networks, drainage pathways, oxidation zones, and organic structure are all part of a functioning ecological architecture. When topsoil is stripped, compacted, mixed with subsoil, or spread back unevenly across disturbed ground, much of that structure is disrupted or destroyed.

Subsoils and weathered parent materials that were never intended to function as rooting horizons are suddenly incorporated into the active soil layer. Natural drainage systems are altered. Compaction increases. Biological communities are damaged and destroyed, fungal connections disrupted, burrows and communities obliterated. In most cases, the resulting instability is then compensated for through increased applications of fertiliser, lime, slurry, reseeding, and drainage infrastructure.

Chemical fertilisers can mask many of these problems for surprisingly long periods. Grass may still grow vigorously if sufficient nitrogen, phosphorus, potassium, and lime are continually applied. Yet the underlying soil system may be increasingly simplified, compacted, hydrologically unstable, and biologically impoverished.

If external fertiliser inputs become more expensive, less available, or geopolitically unstable, the implications could become profound. Without continual replenishment, many improved grasslands would gradually decline in productivity. Acidification would intensify. Potassium deficiencies would emerge. Rushes, scrub, heath, and low-productivity grassland would begin to reassert themselves across parts of the landscape.

In other words, many fields could slowly begin to resemble my own field and garden.

This does not imply imminent collapse, nor does it mean modern farming is misguided. Farming is a business, and farmers need to make a living, and they need to be competitive. Rather, it highlights the reality that modern agriculture in Atlantic western Ireland increasingly depends upon industrial nutrient replacement systems layered upon inherently easily leached and naturally nutrient-poor soils.

The lesson from a simple soil test is therefore much larger than a struggling vegetable garden. It is a reminder that landscapes have long ecological memories. Beneath the appearance of modern productivity, the old Atlantic soil-forming processes are still at work — quietly, continuously, and relentlessly washing fertility toward the sea.

And like so much in modern life, successful farming in West Cork has a very tenuous hold that could quite easily and quickly be disrupted by events elsewhere in the world.