FERTILITY AND CAREFUL CULTIVATION.

Otago Witness, Issue 3277, 3 January 1917, Page 8

FERTILITY AND CAREFUL CULTIVATION.

The fertility of a soil is determined to some considerable extent by its physical character, which depends again on the original nature of the rocks from which

the soil particles were derived. They may have been hard and dense in their mineral character, and so able to resist the solvent effects of air and water, and other agencies, or soft and friable, and easily affected by atmospheric influences. In the formation of a. soil there may have been an absence of vegetable matter, and, in consequence, the soil particles would tend to settle in hard, compact masses, more or less impervious to water, air, and warmth, or the particles may, being coarse and incapable of close compaction, form an open and friable soil, admitting natural active agencies. The removal of crops from the land—continual cropping with no manure—rapidly exhausts the soil of the elements which go to build up the plant, and will bring about in time a worn-out soil. This need cause no surprise if it is realised that plants take at least 10 chemical elements for their norma] growth and development—viz., nitrogen, potash, phosphorus, magnesia, sulphur, silicon, sodium, iron, chlorine, and calcium. Fortunately the necessity of supplying all these elements need not be seriously considered by the farmer, as the drain on the cropped land pertains largely to four main elements, which exist in larger amounts in plants that are grown, and in smaller amounts, than the others in the majority of soils. These four elements, which are our especial concern, are nitrogen, phosphoric acid (phosphorus) potash (potassium), and lime (calcium). 7_here may be an abundance of potash and phosphoric, acid in a soil, but very little nitrogen, in which case good crops of cereals, for instance, could not be grown, because no other element can substitute the nitrogen required by the plant, and it can be obtained by it from no other source than the soil, this group of plants not having the help of friendly bacteria similarly to plants of the legume order, which obtain under best conditions a supply of nitrogen from the atmosphere. The presence of suitable amounts of vegetable matter and good cultivation are conditions that are within the power of all farmers to provide, though it is not always practicable to keep land continuously cover-ad with a cr op—indeed, it is held in some quarters that the loss through leaching is sometimes more than balanced by the gain in other directions. For example, though loss of nitrates may occur, the gain in availability of the mineral constituents — phosphoric acid and potash, with the accompanying improvement in the texture, due to the exposure of the soil to atmospheric influences—more than balances these losses, particularly during the winter, with its wide range of temperature. The need of phosphates of lime for most of the Dominion soils is evident. Phosphates onlv hay_e to be cheap and we all would rush for supplies, as they are a vital necessity in the development of all life, both animal and vegetable. Year after year there is an unceasing dram of phosphates from all descriptions of grazed and cultivated soils, so no wonder many of our pastures have become robbed of this constituent. It is a mistake to think that arable lands are more subject to loss from cropping than pasture lands, and the idea is widely held, unfortunately. Pastures, it must *be remembered, are perpetually robbed by grazing animals. In their case""it has been constant depletion, and while arable lands may get some manurial treatment, pastures are neglected, and are supposed to preserve their fertility through the simple act "of grazing. Phosphate of lime i? an important constituent in the bone construction of ;>ll animals, in the milk of cows, in the wool of sheep, and. in fact, of every part of animals —and only a small proportion is returned in the animal excreta.