PHOSPHATES IMPORTANT

Gisborne Herald, Volume LXVI, Issue 20087, 6 November 1939, Page 7 (Supplement)

PHOSPHATES IMPORTANT

We no longer look upon a strong back and a weak head as being the requisite qualifications of a good farmer. Sheer strength of muscle will not make up for lack of knowledge. Science has progressed so fast during the past decade that it is not to be wondered at that the working farmer has failed to keep fully abreast of the latest discoveries and inventions. Practically without exception changes have taken place in every phase of agriculture, so that the up-to-date agriculturist is really more a scientist than a farmer. This applies particularly to the grassland farmer, who depends upon top-dressing fertilisers to maintain production. It is by no means uncommon to find one farmer in a district outstandingly successful, simply because he is a stop ahead of his neighbours in the matter of fertilisers.

Just a year ago a well-known Waikato dairy-farmer was seriously perturbed because his pastures were not moving away as he expected them to in September and October. He had been top-dressing very generously for some years, but still he was always inclined to be short of feed on his well-stocked area. Early this year this man read an article dealing with phosphate fixation in Waikato soils, and recognising the description of a particularly bad soil type as being exactly what he was working on himself, he took immediate steps to protect his phosphate applications from fixation as insoluble compounds. A dressing of lOcwt. of lime to the acre over the whole area of his grassland, followed by little more than half his usual application of superphosphate in the autumn, has given him more feed than he knows what to do with this season.

Phosphate Fixation It would appear from what has been written recently on this subject that considerably more attention must be paid to it if farmers are going to secure maximum results from the use of phosphatic fertilisers. The position briefly seems to be that when phosphatic manures are added to the soil, the phosphoric acid, which is the plant-food, is either, taken up by the plants or forms compounds with other minerals in the soil. The compounds usually formed are those between the phosphoric acid and lime, which is called phosphate of lime; phosphoric acid and iron, called phosphate of iron; and phosphoric acid and alumina, called phosphate of alumina. It is only when a compound of phosphoric acid and lime is formed in the soil that the plant-food contained therein remains at the disposal of plants. Consequently in the absence of sufficient lime in the soil the phosphoric acid supplied in the form of super may not be 100 per cent available. In actual practice that is being demonstrated on many soil types in the north. For instance, in the North Auckland district, on what is known as the rod-brown loams, superphosphate alone fails to make any visible improvement to pastures until the third or fourth application. The same results follow the use of any sort of phosphatic fertiliser, but first give the soil an application of carbonate of lime at the rate of one ton per acre, and then superphosphate will work wonders. The officer in charge of experimental work in the north sums up the position in these words: “Lime is required to make phosphates do their work efficiently, and lime and phosphates are required before potash can give any worth-while result.”

Residual Effect of Stlper It is commonly held that because , superphosphate is a quick-acting ferti- t liser, its usefulness is very short-lived. < That is not at all the ease, as has been proved and demonstrated on numerous , occasions. In Otago Mr. R. B. Tennent, ; now director of the Fields Division, ) Department of Agriculture, but then j tricts, found that an application of ' in charge of Otago and Southland dis- £ creases over no manure in three j superphosphate gave significant in- i successive hay crops. i An interesting experiment carried f out over the past few years in Scot- j land credits superphosphate with r definite beneficial results over three f successive crops, turnips, barley and j hay. In fact, the experiment goes <

PROFITABLE FARMING

further than that, as it shows the residual value of superphosphate compared with that of basic slag, bone meal and finely ground mineral phosphate. The results of this experiment, as published in the Scottish Journal of Agriculture, may be summarised as follows: 193 G, turnips, limed ground, yields: Super. 450 cwt.; bonefiour, 440ewt.: basic slag, 410 cwt.: mineral phosphates. 370 cwt.; control, 325 cwt. 1937, barley, limed ground, yields: Super, 78cwt.: slag, 76ewt.: control. 73cwt.; mineral phosphates and boneflour. 72cwt. 1938, hay, limed ground, yields: Super, 33cwt.; slag, 34cwt.; mineral phosphates and bonefiour, 33cwt.: control, 32cwt.

It is important to note that after the initial treatment of the various plots in 193(5. no further applications of phosphates were made until after the hay harvest in 1938. It is also of interest to note that whereas the basic slag was used at the rate of Bjowt., super was used at the rate of Bcwt. per acre. Expressing the result from super as 100 per cent on each crop—that is, 300 per cent over the three years—the others in order read: Basic slag. 290 cwt.; boneflour, 290 cwt.; mineral phosphate, 275 cwt. Discussing these results, the author of the report states: “It is of interest to note that superphosphate, the only water-soluble phosphate, is by no means completely used tip or rendered unavailable in the first year after application, but has a marked residual

value.” An Australian Experiment

The Victorian Department of Agriculture has been conducting manurial experiments on wheat and oats at Werribee, and they have found there that -after 10 years’ manuring with superphosphate yields continued to be satisfactory for two years, during which further applications of super were withheld. At the same time it is pointed out that those results should not be interpreted to mean that the farmer can discontinue using .superphosphate even under conditions ot high soil fertility. Although it may take 10 or 12 years to build up a fertility reserve in the soil, it will be found that it diminishes quickly if superphosphate is not regularly applied The fact that it is always phosphates that are recommended for top-dressing pastures and even for application with various crops, does at first glance seem to be inconsistent with the text-book statement that a very wide range of minerals is required for the complete sustenance of plants. In stressing the importance of phosphates one is not unmindful of the importance of other plant-food elements; it is just a case of laying emphasis upon what may truly be called the corner-stone of our agricultural structure. The position is most effectively stated by the late Charles E. Thorne, who pioneered some classical experimental work at Ohio Experimental Station, U.S.A.. when he said: "The ultimate function of agriculture is to feed and clothe humanity, and the most important element in human food is phosphorus. Under existing conditions the greater part of the phosphorus consumed by mankind eventually finds its way to the sea or to the cemetery, so there is a steady flow of this element from the soil which is never returned. Whenever, therefore, the land has been under

cultivation for any considerable length of time, there will be a deficiency of phosphorus, except in rare instances in which the soil has been naturally stocked with an abnormal supply of this element." There are no North Island soils that we know of so stocked with an abnormal supply of phosphorus, so that phosphatic manuring becomes a fundamental necessity on all soil types. The maintenance of fertility is largely a matter of keeping up the supply of | phosphates and calcium, arid this will I best be done by liming when timing I is an economic proposition, followed i by regular applications of superphos- I phate, and where liming is not econo- I mic, the use of basic phosphates — g particularly basic super—is recoin- I mended as being the next best pro- I cedure, *