ARTIFICIAL MANURES.

New Zealand Herald, Volume LX, Issue 18518, 1 October 1923, Page 10

ARTIFICIAL MANURES.

MAINTAINING FERTILITY.

EFFECTL OF CONSTANT CROPPING, j - . < _ nx .S. , ' In regard to the- use of artificial manures, which ' in recent years has become so extensive, the question ; is often raised Whether they restore 'all 'the elements of fertility, or only that which enables the crop to draw more largely than it would otherwise do on the natural productiveness of the soil. This is a question which can, only bo satisfactorily answered by a series of carefully conducted experiments, extending over a long period ' of . time. : This the ordinary farmer cannot do, as in most instances, apart from tho cost of experimenting, ho cannot afford to • wait,; because ho must : gel : a quick return .for moneys spent, therefore ho must depend, a, great deal on the information supplied from time to time' by the various expert mcntalists. In. other words, he must to a largo degree, work oil borrowed knowledge,, jus life is too; shorts to ' find ■• out everything for ono's-seK. The application of partial manures'and the constant selling of the crops would no doubt, in course of time, so rob the soil of thoso constituents which tlio manures'did not contain that it would cease to yield good crops, but, when tho crops are"'consumed on tho farm, and the farmyard manure, liquid and solid, is all returned to tho soil from which it was derived in tho form of a crop, little or no exhaustion, but a gradual and in some in- | stances, a rapid improvement as a rule will ensue. < When used to supplement, tho manure produced on tho farm, artificial manures are of great benefit, • but it is open to doubt if they can ho successfully made to take the place of farmyard manure, wholly through a long series of year's. But as it is out of the question in iNevv Zealand to make use of farmyard manuro to any great cxtont, owing chiefly to tho cost of labour and the distance from tho main market for fat stock, the Now Zealand farmer has to depend almost wholly upon artificials to supplement the excreta of the cattle and sheep fed on the land. If, however, an occasional crop is ploughed under in the way of green manuring, in conjunction with the practice ol a thorough system of manuring, the result is usually very satisfactory. Necessary Constituents. On land that has been subjected to exhaustive cropping, or land in a. low state of fertility there can bo little doubt that a proper balance in the four most important plant foods, viz. nitrogen, phosphoric acid, potash, and lime, has a very decided influence on the growth of the plant produced, and tho crop obtained. Each constituent has its particular work to do, and tho absence or deficiency, of any one of them will cause the death or the incomplete development of the plant. Moreover, they are absorbsd during the early stages of growth, A cereal crop contains at the time of full bloom all the nitrogen and potash that are found in the mature plant; the assimilation of phosphoric acid continues somewhat later. It is thus plain that crops require a good supply of these vital constituents of plant-growth in? a readily available form if a crop is to h*?a a chanco of doing well.

Necessity of Nitrogen. In the absence of nitrogen' the . plant makes no appreciable growth. With only a limited supply, the plant commences to grow in a normal way, but as soon as the available nitrogen is used up, the lower and smaller leaves begin to gradually die down from the tips and all the plant's energy is Centred in one or two leaves. Nitrogen ia one of the main constituents of protein, which is possibly the most valuable part of a plant. It is also a constituent of chlorophyll, the green colouring matter of plants, hence with a limited . supply of nitrogen the leaves will have a sickly yellow colour. An abundance of nitrogen will produce a luxuriant, growth of leaf arid stem, but it will retard maturity and with cereals will frequently cause the ( crop to- lodge. Therefore, when crops such as cereals are to bo matured, an over-supply of nitrogen is injurious, but with crops such as rape, kale, or any of the catch crops, an abundance of nitrogen will, other fertilising constituents being present, tend to .produce a strong vigorous growth and give crispncEs, or succulence to these crops. . , Value of Potash. .. Potassium, or potash, as it is commonly called, is. one of the mOst important 'and least variable of all the elements of the ash plants. It is quite evenly distributed throughout the leaves, stem and seed, and generally occurs in the entire planl in the largest proportion of any of the essential ash constituents. The function of potassium is Apparently to aid in the production and transportation of the. carbohydrates. In fact, this element seems to supplement the action of nitrogen by filling out the framework established by the latter. Potash with nitrogen is always an important fertiliser with small crops, where the object is to produce sugarstarch as with sugar beets and potatoes. It is also apparently essential _ for the formation 'of : protein and thus indirectly aids in the formation of all organic matter. Phosphorus to Assist Maturity.

Phorphoruß in the form of phosphates, is found in all parts of the plant, but tends to accumulate in the upper parts of the stem and leaves, and particularly in the seed. An insufficient: supply of phosphoric acid always results in a poorly developed plant, and' particularly in a poor yield of-shrunken grain,, Nitrogen forces leaf growth and phosphoric acid hastens maturity. Calcium, or lime, is a constituent of the stem rather.; than the seed. It has been noticed that soils containing an abundance of lime usually produce well-nourifhed crops that are capable of .withstanding unfavourable climatic conditions such as drought, belter than crops nob so well supplied with lime.