698 . J oiiriial of Agriculture, Victoria. [11 Xov., 1912. 



the action of lime, alumina, and iron compounds in the soil. If this 

 is so, one might naturally ask why superphosphate is so superior to 

 other forms of phosphate, if it begins to revert to more insoluble forms 

 immediately it is applied to the soil; and, why should the manufacturer 

 go to the trouble of converting it into water soluble phosphate? 



The reason for the efficacy of the super, may probably be accounted 

 for by the fact that when it is applied to the soil, the soluble phosphate 

 is dissolved by the soil water or by the rains, and it immediately becomes 

 thoroughly and intimately diffused through the soil before the process 

 of reversion actually takes place. Moreover, in the form of a solution, 

 the particles of monocalcic phosphate are in the finest state of sub- 

 division possible — in a far more finely divided state than could ever 

 be obtained by any process of grinding. It is owing to the infinitely 

 minute state of subdivision of the soluble phosphate and its intimate 

 mixture with the soil particles that its action is more rapid than the 

 other phosphates. 



Hate of Application of Superphosphate . — Opinions differ very 

 widely as to the most suitable quantity of manure to use per acre for 

 a wheat crop. Many farmers apply as little as 30 to 40 lbs. per acre, 

 and consider the dressing quite sufficient ; whilst there are many who 

 use relatively heavy dressings, namely, 1 to 2 cwt. per acre. The rate 

 of cipplicatiun will naturally vary with the soil and rainfall. In 

 regions of light rainfall the dressings are generally reduced to a 

 minimum, whilst in moister districts much larger quantities can be 

 used with profit. In the drier districts heavy dressings may not infre- 

 quently lead to rank and vigorous growth, and in seasons of short 

 rainfall transpiration from leaf and stem goes on so rapidly that the 

 available moisture supplies give out with disastrous results to the crop. 

 Obviously, such a contingency is less likely to happen with crops sown 

 on well-prepared fallows. In considering the most profitable amount 

 to apply, it must be remembered that conditions are such in the wheat 

 areas that the farmer derives a considerable portion of his income from 

 sheep. Consequently, in determining the most profitable dressing 

 to apply, it becomes necessary to consider the indirect effect of the 

 manure on the pasture as well as its mere direct effect upon the crop. 



Now, it is a well established fact that relatively heavy dressiugs of 

 superphosphate produce in Australian wheat soils a remarkalile effect 

 on the pastures. A marked stimulation of the leguminous growth on 

 the stubble and pasture succeeding tlie wheat crop invariably results 

 from heavy dressings of soluble phosphates, and the stock carrying 

 capacity of the pasture is greatly increased. 



Increased stock carrying capacity is quite as important to the cereal 

 farmer as the direct effect of the manure on his crop, for, on the avei'age 

 wheat farm, the returns from sheep, wool, and lambs do not fall far 

 short of those from wiieat. This being the case, it would appear that, 

 if the indirect effect on the pastures is taken into consideration, it is 

 probable that, in moister districts at least, relatively heavy dressings 

 will be far more profitable than light dressings. 



Just what quantities may be most profitably applied in any given 

 district can, of course, only be determined by actual trial. In such 

 trials, however, we should look further ahead than the mere results on 

 the season's crop. 



