LOAM, a soil compounded of various' earths, of which the chief are silicious sand, clay, and carbonate of lime, or chalk. The other sub stances which are found in learns, such as iron, magnesia, and various salts, are seldom in such proportions as materially to alter their nature. Decayed vegetable and animal matter, in the form of humus, is found in beams in considerable quantities, and the soil is fertile in proportion.
According as the learns are composed, so they vary in quality. Those which consist of a great portion of loose sand, with little vege table matter, and with an impregnation of iron, are very unproductive ; and those which contain too much clay, and are on an impervious subsoil, are very difficult to cultivate. But between these extremes there are soils which cannot be surpassed in fertility as wheat-land. What renders loans so much more fertile than either clays or sands is, that the pure earths are in themselves almost entirely barren : sand lets the moisture run through it and evaporate rapidly ; clay retains it, but locks it up in its own substance, and does not allow the tender young roots of plants to push through it ; chalk has the same mechanical quality, besides containing very little organic and soluble matter, from which plants derive their chief increase. Sand and clay alone, without a considerable portion of organic matter, will not snake s. rich soil ; but when a portion of calcareous earth is joined to both, the vegetable matter is more readily rendered soluble, and the clay and sand are prevented from forming a mortar, which would harden too readily, and prevent the influence of the air from reaching the roots. Good loams allow of that circulation of moisture which acts so pro minent a part in the process of vegetation. It is almost universally admitted that the most fertile soils always contain a proportion of calcareous matter ; and by adding chalk to those soils in which it does not abound, whether sandy or argillaceous, a manifest improvement is always produced.
It has been asserted that in the climate of France, in the neigh bourhood of Paris, the best soil for the growth of wheat is composed of equal portions of fine sand, clay, and chalk. Upon what grounds this is assumed, does not appear very clear. The greater the natural moisture of any climate, the greater proportion of sand is required to make a fertile loam ; and the greater the proportion of humus, the less sand will be required to temper the clay. The analysis of soils known to be extremely fertile gives a very great difference in the proportions of the different earths.
In the climate of England the soil which is generally preferred for cultivation is a loam, rather light than heavy; at least half of which is silicious sand, one-third clay, and the rest chalk. Such a soil is called a good loam ; it is land which will produce almost every thing which is usually cultivated on sands or clays : it is not too stiff for carrots and turnips, and not too loose for wheat and beans. It is of most easy cultivation at all times of the year, provided the subsoil be sound, and not too retentive of water. It requires only to be occasionally recruited with manure, to restore to it what vegetation has consumed, and to be kept free from the weeds which naturally spring up in all fertile soils. All attempts to improve the nature of a soil should have for their object the bringing it to a state of loam, by the addition of those substances which are deficient. If there is too much clay, chalk and sand may be added, or a portion of the clay may be by burn ing, in order to destroy its attraction for water, and thus act the part of sand in forming the loam. Limestone or calcareous sand and gravel are still more efficacious for this purpose : they not only correct too great porosity, or too great tenacity, but also act chemically on the organic matter in the soil, rendering it soluble, and fit to be taken up by the roots of plants. If there is too much sand, marl composed of clay and chalk is the remedy. Good loams require much less tillage than stiffer soils, and will bear more stirring to clean them than sands. Hence they are cultivated more economically, and more easily kept free from useless weeds ; while the produce is more certain and abundant. They can be impregnated to a higher degree with enriching manures, with out danger of root-fallen crops, or of too great an abundance of straw at the expense of the grain. For artificial meadows they are eminently proper : all the grasses grow well in good learns, when they are on a dry or well-drained subsoil, which is an indispensable condition in all good land. Sheep and cattle can be depastured on them during the whole year, except when there is snow on the ground. If there should be means of irrigation, no soil is better suited to it than a light loam on a bed of gravel ; or even if the subsoil is clay, provided sufficient under-draining prevent the water from stagnating between the soil and subsoil, which, as practical men very properly express it, would poison any land.