On 12/12/04 2:04 PM, in article , "David
Hill" wrote:

Maybe facts would be better than Thoughts

Soil is limed as and when necessary to counteract its natural tendency to
become more acidic and to create and maintain optimum conditions for plant
growth. Soils may be alkaline (chalk or limestone soils) or acidic (peaty
soils) in reaction. An alkaline soil contains lots of calcium - an element
required in small amounts by all plants. In very acid soils there is a
shortage of calcium salts. The acidity or alkalinity of a soil is measured
on the pH scale, which ranges from zero (exceedingly acid) through 7
(neutral) to 14 (exceedingly alkaline). In Britain most soils tend to be
slightly acidic due to rain constantly leaching out the calcium. Luckily,
most plants will thrive if the acidity of the soil can be adjusted to a
compromise pH of 6.0-6.5. Club root disease of brassicas flourishes in acid
soils but can usually be controlled if the soil can be held at a pH 7.5 (the
upper pH limit for this class of vegetable). Simple soil testing kits,
available from garden centres, enable you to determine the pH of your soil.
They also give a list of plant pH preferences and the amount of ground
limestone that you need to apply to raise the pH by one unit.

It is always preferable to use lime in the form of ground limestone (or
chalk), which is safe and easy to apply. Hydrated lime (slaked lime,
builder's lime) is available but its caustic nature means that it must be
handled with care and applied with care to avoid damaging plants in the
vicinity. If possible, apply the lime in autumn or after winter digging so
that the rains wash it in slowly. Choose a calm day and spread it evenly by
hand. Never use lime at the same time as manure or nitrogenous fertilisers
as it may react chemically with them and reduce their effectiveness. If you
are in a rush, apply the lime to soil that has been raked to a fine tilth
and distribute it by raking well into the top few inches. Water the area and
allow it to stand for a week before applying a nitrogenous fertilise

The RHS have this to say about lime and liming

Liming of garden soils is a long-standing horticultural practice, but the
rationale behind it is often overlooked.

Liming helps to maintain a balance between the soil's acidity and its
alkalinity. This degree of acidity or alkalinity is measured using the pH
scale, ranging from 1 (highly acidic) to 14 (highly alkaline). An increase
in pH from 6 to 7, for example, records a 10-fold increase in alkalinity. A
pH of 7 is neutral, with conditions neither acid, nor alkaline. In garden
soils, you are unlikely to experience soil pH values outside a range of
pH4-pH9.

The optimum pH for most garden plants and vegetables is 6.5 (slightly acid).
If the pH varies significantly from this value, plants may exhibit signs of
nutrient deficiency. High pH levels cause a reduction in phosphate and trace
element availability, while low pH levels reduce the availability of
nitrogen, potassium and magnesium, and discourage earthworm activity.

Clubroot disease
Lime provides a source of calcium and raises the soil pH. It is used to
counter acidity brought about by the effects of certain acidic fertilisers
and the action of rainwater, a weak acid. Soil structure, particularly in
clay soils, may also be improved by lime applications. Reducing the acidity
of soil by liming can encourage improved root development and increase the
number of micro-organisms. These in turn improve the crumb structure and
organic matter levels in the soil ultimately leading to improved crop
growth. Lime can also discourage serious diseases including club root of
brassicas such as kohl rabi.

A soil pH test
It is important to carry out a pH test to determine whether liming is
necessary. If your soil already has a pH of 6.5 or higher, liming will be of
little benefit and may in fact be detrimental. The autumn is the best season
for liming soils, just prior to digging, as the lime can take effect over
the winter months and will not damage young growth. Lime should not be
applied at the same time as organic matter or fertilisers, when it may cause
the release of ammonia, which wastes nitrogen and may damage tender growth.

The two types of lime commonly used by amateur gardeners are calcium
hydroxide (hydrated lime) and calcium carbonate (ground limestone or chalk).
Calcium hydroxide is soluble in water and has a stronger liming action than
calcium carbonate, but is less pleasant to handle and easier to over apply.
Calcium carbonate is now the most widely available and preferred liming
material. It is sold under various names such as carbonate of lime, garden
lime, ground limestone or ground chalk.

Applying lime to soil
Application rates vary with soil type and degree of pH change required. As a
general rule, a loam soil will require an application of 190g per sq m (6oz
per sq yd) of calcium carbonate to raise the pH by half a unit. A clay soil
will require 420g per sq m (12oz per sq yd) and a sandy soil slightly less -
140g per sq m (4oz per sq yd). If a greater change in pH is required, it is
better to add the lime in small amounts over a period of time (rather than
all at once).



--
David Hill

www.abacus-nurseries.co.uk



Hi David
A very informative post. Thanks for taking the time to send it.
Gary
Fort Langley, BC
Canada