222 



Journal of Agriculture, Victoria. \ 10 Apkil, 1918. 



WHEAT MANURIAL TRIALS. 



Five Years' Results. 



By H. A. Mullett. B. Ag. Sc. 



When superphosphate was first introduced as a manure for wheat and 

 dressings of 56 lbs. and even lower than that were advocated, to many it 

 seemed beyond the bounds of common sense that so small a dose could 

 appreciably affect yields. The grounds for this early scepticism are not 

 hard to understand when it is remembered that the top three inches 

 of soil weigh between 300 and 400 tons, and that actually only a fraction 

 (about one-fifth) of the small dressing is of direct benefit to the ulant. 

 To-day so widespread is the use of " super " on our Australian wheat 

 soils and so consistent are the results, that the phenomenal response of 

 the average soil to the manure has become commonplace, and it is only 

 Avhen the seed drill happens to miss sowing the regular quantity of 



Ploughing Manurial Plots at Werribee. 



manure that the farmer is reminded of the vital part which this light 

 dusting plays in producing profitable yields. 



The Importance of DETEitMiisriNG the Most Profitable Dressing. 



The problem of to-day is not, however, one in which the advisability 

 of the use of superphosphate is questioned, but rather to ascertain how 

 much to use. It can be shown that this quantity varies with a 

 number of factors, and that its determination with some degree of pre- 

 cision is a matter of considerable importance. Experiments show that on 

 most soils there is a steady and proportionate increase in the yield as the 

 amount of manure applied is increased until a point is reached after 

 which the same ratio is not maintained, until eventually there is no 

 response to further dressings. Obviously, then, in practice it is necessary 

 to determine the manurial application which gives the greatest net profit, 

 and this is not necessarily that which gives the highest yield. It will 

 follow, also, that the higher the price of wheat the greater will be the 



