PHOSPHATIC MANURES.

Otago Witness, Issue 1920, 4 December 1890, Page 7

PHOSPHATIC MANURES.

The experiments whioh have been from time to time carried out by Professor Tamieson, in Sussex and Aberdeenshire, have attraoted a good deal of attention, and it is of interest to know that those last year were very materially assisted by a grant from the Minister of Agriculture. The more interesting oneß were those that had for their objeot the discovery of the relative effect on plants of different kinds of phosphates, and especially of the natural mineral known as coprolite. The question was somewhat old, but it was important that new trials should take place, as a new phosphate had been introduced into the market, whilst an improvement had been made in most phosphates in regard to the state of their division — a condition which very greatly influences their effect on plants. In 1889, in Sussex, and also at Glasterberry, Aberdeensbire, experiments were commenced. Tho different phosphates taken as types were coprolite, slag phosphates, steamed bone flour, precipitated phosphate, and superphosphate. The prices of these are put in the report at about £3 10s, £2, £6, £10, and £3 per ton respectively. It ib well that the report adds :—: — "These prices are most delusive to those who do not inquire into the composition of the Buostances, and, as it is feared many do not take into account the composition, those manures sold at the lowest price per ton are generally regarded as the cheapest." The following figures will show the fallacy of this idea :— " Of ooprolite there would be required 7091b to provide 751b of phosporuß, which at 33 Ci a cwt would cost 223 . per aero ; of, slag there would bo required 11961b to provide 751b. which at 2a p6r cwfc would ccst 21s 2d per aero ; of steam bone flour Go4lb would bo required to provide the same amount, which at 63 per cwt would cost 32s 5d per acre ; of precipitated phosphate the amount would be 3811b at 10a per owt» or 2 343, per acre; fand af superphosphate to produce 751b of phosphorus 13001b would ba required, which at 3s per cwt would cost 34s 9d." Thus, the report adds, the superphosphate is the dearest form of phosphate of lime for manure. The percentage of. phosphorus on which the calculations of the above costs were mude are those actually fouud in the manures experimented with. Former experiments had shown that all these phosphates, oxcoptslng, could be made use of directly by the plant, and that the degree of usefulness I varied according to (i) the state of division, (ii) freedom from injurious weather. Steamed bone flour iB generally the best divided, but there is room for improvement to-day in thia particular. Superphosphate, we learn, always, and precipitated phosphate frequently, contain [ injurious matter. In regard to rate of action steamed bones^ coprolite gave the best result, the others being too quick or too slow. Tha new trials bad special reference to tho action, of sl&g, and especially to find if it supported or refuted the theory } that insoluble mineral phosphate could be used directly by tho plant. The experiments at both stations in 1888 and 1889 showed that (i) the phosphate in slag can be assimilated by the point; (ii) that this power of the plant is not limited to the natural I mineral coprolite, but extends to tho artificial cr [manufactured, form; (iii) that the insoluble

mineral doctrine coprolite started in Aberdeenshira 15 years ago, and since supported by other experiments, is now supported by the action of slag ; and (iv) that_ the possible prejudicial effect of the iron in slag which was apprehended does not takG place. As a matter of faot, the 'experiments show that slag is nothing superior to ooprolite in the same state of division and hardly equal to steamed bone flour.— Mark Lano Express,