Now we've moved to a garden with claggy clay soil, the state of the soil in this country - and how to improve our soil here in this garden - is of great interest to me.

How allotment holders are kings when it comes to soil management*

Soil is one of the great failures of modern intensive agriculture.  Healthy soils, beneath natural grasslands and - especially - woodlands, contain lots of organic matter that holds on to nutrients and gives soil structural stability, allowing it to resist damage by, for example, heavy rain, thus preventing erosion. 

There's also plenty of life in a healthy soil, lots of burrowing earthworms, so lots of pore space too.  A healthy soil is basically a giant sponge, which fills with water after rain gradually releasing it to plants in dry weather.


When land is cleared for agriculture, and especially for arable crops, all that goes out of the window.  The organic matter is lost to the atmosphere as CO2, and the soil loses its structure and strength, leading to compaction and erosion.  Arable soils also lose their ability to retain water, nutrients and pollutants, leaking nutrients into groundwater and lakes and rivers, causing eutrophication and, if the water is for human use, the need for expensive water treatment.

Although this is all well-known, the conventional view is that soil degradation is the price we have to pay for high yields of arable crops.  But new research in the Journal of Ecology says that gardening proves the conventional view wrong.

The researchers looked at the properties of soils on allotments in Leicester, along with those from other urban sites, and compared them with soils beneath arable local fields and pasture.


The arable soils showed the usual symptoms: compacted, lifeless and low in organic matter.  Allotment soils, by contrast, were more open, more fertile, and higher in organic matter.  The reason isn't hard to find: composting of allotment waste is virtually universal, most allotment holders also import household green waste, and use of manure and other kinds of commercial compost is widespread.  In short, soils on allotments are healthy because people take trouble to keep them that way.

Nor are these healthy soils any barrier to high yields.  During WW2 Dig for Victory campaign, allotments and gardens provided around 10% of food consumed in the UK, despite covering less than 1% of the area of arable cultivation.

Recent research also shows that gardens and allotments produce yields between 4 and 11 times greater than conventional agricultural crops.

In fact soil organic matter is now so low beneath many agricultural soils that it makes it increasingly hard to maintain high crop yields.

These results are not unique to allotments: soils in private gardens were pretty good too.  In fact, garden soils beneath trees and shrubs were best of all, presumably because they are undisturbed and also benefit from the organic matter added by fallen leaves.

Nevertheless, allotments are unique in the way they manage to combine a productive 'agricultural' function (ie growing food) with healthy soils.


So, encouraging people to grow their own food simultaneously targets food security, bolsters the well-known health benefits of gardening, and helps reduce climate change, flooding, pollution and erosion.  

* from an article by Ken Thompson in the Telegraph

See also: http://www.sheffield.ac.uk/news/nr/allotments-could-be-key-sustainable-farming-1.370522

Interesting reading from the past:  http://davesgarden.com/guides/articles/view/3997/#b

Some advice from the RHS: http://www.rhs.org.uk/advice/grow-your-own/allotments