Not many people realise that soils are alive, but in fact there are more living organisms in a teaspoonful of soil than there are people on the planet.

As with all living things, soils can become unwell and even die if they are not cared for properly. All farmers should make pedology - the scientific study of soils - their particular care.

A clod of earth, seemingly simple and lifeless is in fact highly complex in structure. It is composed of elaborate particles with numerous invisible crevices that are inhabited by myriads of inconceivably small organisms. Our very existence is dependent on those microscopic life forms that produce food to nourish the plants which constitute such an important part of our food chain, as well as removing from the soil substances that would be harmful to us.

No two fields on a typical farm have similar soils, and even in the same field there can be several different kinds. There is a lot of truth in the old farming adage that "you need to plough a farm to get to know it".

Fertile soils contain adequate supplies of the main plant nutrients such as nitrates, phosphates, potash and sulphates as well as trace elements like manganese, copper, cobalt and selenium. Above all else, a fertile soil will be free draining and not too acid -and that's why lime is so important.

Liming has been a major factor in British agriculture since time immemorial and there are many historical references to its use on arable soils. The very large dressings - chiefly of chalk - which were applied in the nineteenth century created reserves which lasted for many years. As crop yields increased with the introduction of better varieties and higher standards of farming, this capital was gradually used up, not only under arable farming, but also where grassland and livestock management were improved and dairying became more intensive.

The drains on reserves were intensified in times of agricultural depression, when farm incomes fell and liming tended to be ignored. This loss of fertility could not be allowed to continue indefinitely, and in the 1930s with the growing threat of war, the Government took a hand in encouraging the use of lime with the object of restoring fertility to neglected land and helping the country become more self-supporting in food production. It is widely held by practical farmers that liming improves the structure of heavy soils, reduces "stickiness", lightens cultivations and makes it easier to break down clods to obtain a satisfactory seedbed. In the days of horse cultivations, it was often said that after liming "four-horse land" became "three-horse land" or even less.

Lime, together with phosphate, plays an essential part in the production of animal bone and of milk, and therefore the lime status of the soil is important for the welfare of animals dependent upon crops produced from the land. It is particularly important when they depend mainly or entirely for their nutritional needs on foods grown on the farm, as for example, when stock is expected to find all its requirement from grazing.

The benefit of liming acid grassland may be both direct and indirect. The productivity of the sward is increased and the land will carry more stock. The lime content of the sward improves - mainly because liming encourages the growth of better grasses, which contain more lime than the poor, acid-loving grasses they replace. The proportion of clovers in the herbage also increases with liming, and these plants are rich in lime, and also in protein, than even the best of the grasses. Thus, a correctly limed and manured sward has more clover and good grasses, and is both more palatable and more nutritious to livestock.

Losses of lime from the soil are due to various causes such as removal in crops or livestock sold off the land, losses in drainage water and the effects of acid rain and fertilisers. Of all these possible causes, leaching from the soil in drainage water is undoubtedly the most important. That means farmers have to keep periodically topping up lime levels in their soils. Many, particularly livestock farmers in the Scottish uplands, have not been doing that as frequently, if at all, since lime subsidies were stopped in the 1970s.

Lime has been called the basis of all good farm husbandry. Sadly, there is very clear evidence that large parts of our uplands are becoming impoverished of lime and, as a result, incapable of productive livestock husbandry.