LIME VERSUS BASIC SLAG.

Taranaki Daily News, Volume LVI, Issue 81, 31 August 1914, Page 3

LIME VERSUS BASIC SLAG.

(To the Editor

Sir, —In your issue of 25th inst. you publish a letter over the signature of G. Ingster, the statements contained in which, show that the writer has little or no knowledge of the science of agriculture or iho would not make such ridiculous statements as he does. He asks what element of plant food does Slag contain, and answers GO per cent, of lime, 20 per cent, of phosphates, and 20 per cent. iron. It is news to me that iron in Slag is regarded as plant food. I have always thought that Slag was purchased for the phosphates it contained only; anyhow, that is the basis of valuation on'whic/h it is sold to the farmer. The iron and lime arc only in its composition incidentally. When a man purchases a joint of beef, Jie has to take any bone that meat happens to contain, although ho cannot eat the bone, and the farmer cannot supply the beast to the butcher without the bone in the animal. Similarly, Slag being a bv-product of the iron works, has iron iii its constitution, but the farmer does not pay for the iron—he pays only for the phosphates. Phosphates cannot be administered straight to the plant in. tho form of phosphoric acid because the plant would be. quite unable to assimilate it in that form—in fact, it would kill the plantjust in the same way that one could not live by eating butter pure and nothing but biitter—such diet would kill one—but used in conjnetion with other materials in proper'proportion, butter is a valuable food. Vow. the writer further says lime will do all that -Slag does. Can he tell us where the plant is to get the muchneeded phosphates from if lime and lime alone is employed? It is agreed amongst all students of agriculture that phosphates are one of the most important plant foods, yet lime alone provides no phosphates, nor will the application of lime alone manufacture any phosphates in the soil. Lime has many useful functions to perform 'in the economy of agricultural pursuits, and I have for many years been a strong advocate of its use under certain conditions, but to urge its use in place of proper plant foods such as phosphates, potash or nitrogen, is only to show one's ignorance of the rudimentary elements of applied agricultural science. , , It is a true saying, a little knowledge is a dangerous thing.—l am, etc., II W. LAWRENCE, F.C.S. (bond.)

rhemical Laboratory, Jolinsonvillc, Aug. 27,