A profile of a typical 'podzol' showing the grey layer of leached out minerals below the dark top level of soil
A profile of a typical ‘podzol’ showing the grey layer of leached out minerals below the dark top level of soil

This week, ‘Gardener’s Question Time’ features soil. A Mr. T. Breck asks:

‘What is a soil pan? I think I may have one in my sandy soil here in south west Norfolk, as my plants don’t seem to be growing very well. Can I do anything to get rid of this?’

Well Mr. Breck, it does sound as though you may have a soil pan. This occurs when certain soil minerals are washed down through the soil by rain lodging some way below the surface. It does often happen in sandy soil containing a high proportion of iron. Over a period of time the minerals weld together to form a hard layer impervious to water. This layer restricts the downward spread of plant roots, so that poor growth results. In former heathland or coniferous forest areas (which is broadly speaking what much of south west Norfolk used to be) these soils may be termed ‘podzols’.

A similar situation can happen if a rotary cultivator is used regularly and its tines  are set at the same depth on each occasion – the action of the tiller blades causes soil compaction at that depth. You can avoid creating this pan by varying the depth of the rotivation.

To remove a pan it’s a case of digging deep and using a pick or fork to break up the welded layer of minerals and incorporating as much organic material (leaf mould, compost, manure) with the replaced topsoil.

More difficult hardpans may be further improved through the action of both adjusting the soil pH with lime if the soil is acidic, and with the addition of gypsum. This combination can help loosen clay particles bound into a hardpan by the actions of hard salts such as iron, calcium carbonate and sodium, by promoting their mobility. It is likely that mechanical removal of the soil pan and some changes to the soil structure as suggested above will be the most successful strategy, rather than relying on just one approach.

Adding home made compost or other organic matter to your soil will improve its structure and nutrient levels

Adding home made compost or other organic matter to your soil will improve its structure and nutrient levels

Whilst we are talking about soil it is perhaps worth just noting what soil actually is. It is made up of many different ingredients including varying proportions of clay, silt and sand. A soil containing a high proportion of clay is considered to be heavy and, whilst rich in nutrients, is often difficult to cultivate, especially when wet. Sandy soils, on the other hand, are light and easy to work, even after rain.

The soil here in the Old School Garden is a sandy loam and is a joy to cultivate, though I do have to add organic material to improve its moisture retention and nutrient levels. So, decomposing plant remains (or other organic material) is another important ingredient of soil as are air and water. Microbes by the million are also present and these and other organisms like earth worms are doing the job of breaking organic material down and  processing this into soil.

Links:

Improving soil by adding organic matter

The importance of organic matter

Compost – 10 things you wanted to know, but were afraid to ask…

Old School Gardener

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