FEEDING PASTURES

Taranaki Daily News, 2 May 1935, Page 5

FEEDING PASTURES

SUPPLYING WORLD WITH MANURES. INTERESTING OUTLINE OF WORK. In a determined endeavour to maintain or increase the productivity of pastures arid agricultural lands heavily cropped year after year, the scientist hai learned how to make manure from the air itself. A large proportion of sulphate of ammonia, a fertiliser used extensively as topdressing for grasslands all over the world is now produced by a process in which the free nitrogen is recovered from the atmosphere. The ingenuity of devices to supply manures which make up for soil deficiencies caused by intensive cultivation is remarkable. In an address to members of the New Plymouth Round Table Club yesterday, Mr. J. L. Mander gave an interesting account of the origin and properties of artificial manures • almost universally used in agriculture to-day. More than 95 per cent, of the exports of the Dominion to-day were derived from its grasslands, he said, and the increasing appreciation of the properties, of artificial fertilisers was shown by the fact that less than 300,000 acres were topdressed in 1914 against 2,250,000 acres today. Even so only 20 per cent, of the land was being top-dressed annually and of this 50 per cent, was in the Auckland province. The huge increase in the productivity of the Auckland farm and grass lands was well known.

Sulphur, iron, lime, magnesia, potash and phosphates were the soil properties most commonly exhausted by intensive cultivation. Lime, while not actually a plant food, possessed the property of making the soil give up the concentrates it possessed. Nitrogenous fertilisers were for the most part supplied by preparing bone, meat and animal offal in special forrhs which were, however, very slow acting. Nitrates were supplied as chemical salts such as nitrate of soda and sulphate of ammonia. The first chemical was found in large Chilean deposits and the second, until comparatively recently, manufactured as a by-product of coal. The process now in use, however, was one which actually took the chemical from free air and had been developed in the war years by Germany to overcome her difficulty of supply. Thus had Sir William Crook’s prophecy that the world would be faced with starvation as a result of a nitrates famine been disproved. Almost every country in the world to-day was using synthetic sulphate of ammonia and Chile’s export of nitrates had dropped from 3,000,000 or 4,000,000 tons annually to 1,000,000 tons. Potash deposits were almost exclusively confined to Germany and Alsace but it was notable that Britain had obtained the rights of working the Dead Sea waters to obtain supplies of this essential manure. Excellent potash manure could be obtained from the ash of burned seaweed. Wood ashes contained less than one per cent, of potassium. Phosphates were largely supplied in the form of superphosphate, guano, basic slag and ground rock phosphates. Their value lay in the promotion of quick root growth.

Rock phosphate came mainly from Nauru and Ocean Islands—territories held under mandate from Germany and run by a phosphate commission. Guano was also obtained in island deposits and was formed as a result of the action of lime on the accumulated excrement of fisheating sea birds. The Value and rapidity of action of a phosphatic manure was largely determined by its solubility. Superphosphates—rock phosphates treated with sulphuric acid—were the most rapid of all in action, being soluble in water whereas most other forms were soluble only in weak soil acids.

Basic slag was a by-product of steel works specially ground and prepared and its grade, also, was determined by its solubility. Modern processes of steel manufacture did not tend to improve the quality of slag, with the result that fertiliser firms purchasing from the continent had to have very careful tests taken to assure the quality of the product. Mr. Mander pointed out that three of the five fertiliser works supplying the farming communities of the North Island were situated in the Auckland province and stated that in bis opinion, the farmer who adequately supplied his land with the plant foods it required could s. increase his production that he need not worry about low prices. Modem science had supplied him with everything he required.