FERTILISERS

Hokitika Guardian, 18 July 1929, Page 2

FERTILISERS

ACTION EXPLAINED. A LECTURE FOR GARDENERS. The importance of the correct use of organic manures was stressed by Mr M. Davey, of the Department of Agriculture, in his weekly lecture to W.E.A. students at the Trades liali on Friday evening. The speaker saici that while the supplies of food taken up by the leaves from the atmospuere are practically inexhaustible, this tloes no apply; to the food in the soil, as it may.;bpcome exhausted or may only exist infvery small quantities in the first place. When such a shortage exists it is necessary to resort to manuring, and this must be done with intelligence, otherwise much money can be wasted. The first c-onsidera-tion is to find the requirements of the crop, and whether there is a deficie icy in the soil. This can best be ascertained by soil testing with a- few plants in boxes, as by'adding different quantities of .various fertilisers the most beneficial additions to the soils can be arrived at. Of important soil constituents an average soil contains 15 per cent of nitrogen, 15 per cent of phosphoric acid, and 4 per cent of potash,, and bv working out the totals these quantities would represent in the top nine'inches of soil, we are able to ascertain that there is much more than any crop can. or does, utilise, and that the plant food contained in the soil murt be very largely in an insoluble state which the plant cannot assimilate, It is this deficiency of available plant food which has to be made up by supplementary supplies,Most crops require access to oxygen, hydrogen, nitrogen, carboh,; phosphorus, . potassium, calcium, sulphur, magnesium, and iron, and as a general rule only three subsianco ar e apt to be deficient in supply. These are nitrogen, phosphorus, and potassium, and hence there are three main classes, of manures, nitrogenous phosphatic, and potassic. In exceptional cases calcium is so deficient in a soil that crops cannot obtain all they require and limeing has to be resorted to,. but generally lime is applied’ top Amend the soil rather than supply; plant food, In cases where manures contain the]three main substances referred to. they are known as complete manures. ■

THE VALUE OF BONE MANURE. In considering the use of phosphatic manure,, Mr Davey said that • the; fertilising' effects of hones has long ; been realised, but it is only within comparatively recent times that the attention of experts has been directed to the phosphoric acid which they contain in large quantities and which is their most valuable constituent. It occurs in several different chemical forms, but all the pliosphatio manures of any importance are phosphates of calcium, and these the lecturer dealt with under their various headings. In. regard to thenfunctions, he explained that they greatly stimulate root formation, and thus hasten the growth of the plant. This is particularly valuable in the early stages of a plant’s life, as it enables the root to reach the lower levels of the soil and renders it more immune to the effects of drought. Phosphatic manures are very farreaching in their effects on plant life, especially from a farmer’s standpoint, in regard to improvements in food values for stock and horticulturists should -note; the beneficial effect they have on legumes, due largely to the stimulation of the nirogenous bacteria which associate themselves with this class of plant. Peas, beans, and some ornamental shrubs belong to this order, and can generally receive phosphatic manures to advantage. Mr Davey explained the process of manufacture of the manures dealt with, and referred to the differences between the two most important phosphatic manures as follows:—Firstly, superphosphate is acid in its action, 'while basic slag is alkaline; secondly, the phosphoric acid in superphosphate is immediate in its action, while that in basic slag is retarded by its combination with lime. In treating heavy clay soils the latter should be used in preference to super as the mechanical condition is improved by the lime content, because the clay usually contains sufficient moisture to act on the manure. In the application of superphosphate the general impression among gardeners is that the continued use of this manure tends to make the soil sour. Mr Davey stated that many years of experience in England and persistent use of the manure in New Zealand had proved this assumption to be incorrect. It did not produce a harmful effect upon the soil, while it improved the general condition of the plants.

NITROGENOUS FERTILISERS. Passing on. to the subject of fertilisers, the lecturer pointed out that nitrogen is m:i/inly eonecimed with the vegetative growth of the plant, and a deficiency of nitrogen results in stunted growth. On the other hand, an exoessive use of this manure causes rank and weak growth, thus rendering the plant open to the attacks of disease. One of the most marked effects of the result of applying nitrogen is the pronounced increase in the green colouring matter of the leaves and a general expansion of the foliage. Tfie most important forms of nitrogenous manures were consul: ered, and many of these are now procurable jin highly-concentrated and

roadily-soluble forms, which are very good, and have the advantage of saving freights and labour. Reference was made to the value of dried blood, which is frequently mixed wiih bones and sold as blood and bone manure, and may be regarded as a sale and useful manure lor m,ost crops and represents a fertiliser occupying a position between chemical fertilisers and organic manures. It 'is I airly rapid in its action under moist conditions, which hasten* its dissolution by soil micro-organisms, thus rendering the nitrogen soluble. The various kinds of bone 'manure form a class of fertiliser’which combines both the phosphatic and nitrogenous, and being slow but very safe in action, may be specially recommended to horticulturists rather than to tannins, who require to procluc their crops to more definite than the garrleu-

The last class'of manures dealt with was the important f one containing p'otash, which ".‘influences the starch production of the plant. Its lorn and vigour are dependent on an adequate supply of potash, especially certain classes of plants, such as legumes. A few of the gulden crops particularly benefited by direct applications of potash are potatoes, tomatoes, licet, and onions. It hardens plant tissues and increases resistance to disease, and is veiy valuable in correcting the adverse effects of excessive applications of nitrogen. The subjects discussed in the next lecture will be the selection and valuation of manures, and the propagation and reproduction of plants.