Sandy soils are usually considered to be easily cultivated, but serious
problems can occur because the particles readily pack together,
especially when organic matter levels are low. Consequently many sandy
soils are difficult to firm adequately without causing over-compaction.
Pans near the surface caused by traffic and deeper cultivation pans
frequently occur on sandy soils, resulting in reduced rooting and water
movement. Subsoiling is frequently undertaken on a routine basis every
4–6 years, although the need can be reduced by keeping machinery
off land while it has low load-bearing strength and by
encouraging natural structure-forming agents.
Coarse sands have low water-holding capacity, which makes them
vulnerable to drought, particularly in drier areas. This is not such a
disadvantage if irrigation equipment is installed and water is readily
obtainable. In many categories of horticulture there is a demand for
soils with good workability. Coarse sands, loamy sands and sandy
loams have the advantage of good porosity and can be cultivated at field
capacity. Sands tend to go acid rapidly and are vulnerable to overliming
because of their low buffering capacity.
Silts and fine sands
These can be very productive soils because of their good water-holding
capacity and, while organic matter levels are kept above 4 per cent, their
ease of working. However silts and fine sands present soil management problems, especially when used for intensive plantings, because they
have weak structure, are vulnerable to surface capping, and are easily
compacted to form massive structures. To achieve their high potential,
efficient drainage is vital to maximize the rooting depth. Fine tilths
in the open should be avoided, especially in autumn and early spring,
because frosts and heavy rainfall reduce the size of surface crumbs. For
the same reason, care should be taken with irrigation droplet size that,
if too large, can damage the surface structure. Improving soil structure
is not easy after winter root crop harvesting or orchard spraying on wet
soils, because low clay content results in very little cracking during
subsequent wetting and drying cycles. Improvement therefore depends
on other natural structure forming agents or on subsoiling.
Clay soils tend to be slow draining, slow to warm up in spring, and
have poor working properties (see soil consistency). A serious
limitation is that the soil is still plastic at field capacity, which delays
soil preparation until it has dried by evaporation. Permanent plantings
are established to avoid the need to rework the soil. Playing surfaces
created over clays have severe limitations, particularly when required
for use in all-weather conditions. Where high standards have to be
maintained, as in golf greens, fine turf is established in a suitable
growing medium overlying the original soil. However, a high clay
content is an advantage for the preparation of cricket squares where a
hard, even surface is required but is played on only in drier weather.
Increasingly, heavily used areas are replaced by artificial surfaces.
Horticultural cropping of clays is limited to summer cabbage, Brussels
sprouts and to some top fruit in areas where the water table does not
restrict rooting depth. Under-drainage is normally necessary. In wetter
areas most clay soils are put down to grass. Timeliness, encouraging
the annual drying cycle of the soil profile and maximizing the effect of
weathering to help cultivations are essential for successful management
of clay soils.
Peat soils have very many advantages over mineral soils
for intensive vegetable and outdoor flower production. Fenland soils
and Lancashire Moss of England; peatlands of the midland counties
of Ireland; the ‘muck’ soils of North America; and similar soils in the
Netherlands, Germany, Poland and Russia have proved valuable when
their limitations to commercial cropping have been overcome.
Well-drained peat at the correct pH is an excellent root environment.
It has a very much higher water-holding capacity than the same
volume of soil and yet gaseous exchange is good. Root development is
uninhibited because friable peat offers hardly any mechanical resistance
to root penetration. This leads to high quality root crops that are easily
cleaned. These cultivated peat lands warm up quickly at the surface
because the sun’s energy is efficiently absorbed by their dark colour, with consequent rapid crop growth. These soils have a very low power requirement for cultivation, are free of stones, and can be worked over
a wide moisture range.
Plant nutrition is complicated by natural trace element deficiencies and the effect of pH on plant nutrient availability. Peat has poor load-bearing characteristics and specialized equipment is often needed
to harvest in wet conditions. Whilst peat warms up quickly on sunny
days, its dark surface makes it vulnerable to air frost because it acts as
an efficient radiator. Firming the surface and keeping it moist combat
this. Weeds grow well and their control is made more difficult by the
ability of peat to absorb and neutralize soil-acting herbicides. The high
organic matter levels also make the peats and sandy peats vulnerable to
wind erosion in spring when the surface dries out and there is no crop
canopy to protect it.