Lime
The application of Lime as a manure to certain soils has long been practised, and has been attended with excellent results, in rendering them productive, and bringing, by its chemical action, the component parts into a proper condition for being absorbed by the roots of plants. Lime is not naturally found in a free state, but is plentiful in combination with carbonic acid, forming what is termed Carbonate of Lime. In the process of burning usually adopted, the carbonic acid is driven off, and the substance left (Quicklime) has a powerful affinity for water, either for absorbing it rapidly when placed in contact, or more slowly from the atmosphere. Quicklime is extremely caustic, and possesses the power of decomposing animal and vegetable substances; hence its fertilising value on soils containing a large quantity of inert vegetable matter, such as recently broken-up grass land, or that where there is a quantity of peat, consisting of roots and fibres, that would otherwise long remain in an undecomposed state. Lindley, in his "Theory of Horticulture," states that "when this substance (Lime) is mixed with decaying matter, it hastens its decomposition, and renders it more easily assimilable by plants. This is its chief horticultural value, if regarded as a manure. In old cultivated land, rich in humus, it suddenly increases productiveness in a remarkable degree; increasing the properties of dormant animal or vegetable manure. Hence it has a most important effect in kitchen gardens. But Limed land soon loses its productiveness unless manure is subsequently applied, and poor soils are soon run out by it. To some plants, such as many Conifers, it is injurious; to others it appears to be an indispensable article of food, such as Potatoes, Sainfoin, Barley, Beetroot, Peas, Clover, &c." Although Lime itself is thus apparently a necessary element in the food of many plants, it is more especially valuable in soils by rendering other constituents soluble, and reducing them to a state in which they may be absorbed and assimilated. In applying Lime to any land, some caution is necessary, as it possesses the important property of expelling or setting free ammonia, one of the indispensable constituents of plant-food. Where farmyard manure has long been used, a light application of Lime may be of great advantage in hastening decomposition; while, on the other hand, soils which contain but a small amount of organic or vegetable matter, might, by similar dressings, become exhausted. Peat and clay soils, or those recently broken up after forming grass-land, are acted upon most beneficially by Lime, the effect produced depending greatly on the amount of organic matter contained in each. It should be applied as a top-dressing, or be well incorporated near the surface of the soil. One of the best methods is to form a compost of spare earth, weeds, or organic refuse of any description, for spreading over the ground, and mix a large proportion of Lime with it. The latter substance contributes its own fertilising effects to the mixture, and, at the same time, exerts its influence in many other ways. The application of Lime has been recommended, in some cases, to the extent of 200 bushels to an acre; but a quarter or half of this quantity will, perhaps, in the majority of instances, be sufficient to effect the desired purpose. An experiment should be made with a small portion of ground, in the first place, and, if the results prove favourable and marked, a larger portion might be treated under similar or altered conditions, according to the amount of success attained. The presence of Lime in the soil is very hurtful to Rhododendrons, and many other hard-wooded plants of a like nature, grown in the open air. It is also most destructive to hard-wooded Cape and Australian plants, cultivated in sandy-peat soil, under glass. Lime being, to a certain extent, soluble in water, the use of that which contains any large proportion should, if possible, be avoided in the cultivation of all the plants just referred to. Rain-water contains much less than any other; consequently, it should be preserved and utilised to the fullest extent in preference to that obtained from wells, springs, or other sources.