28''^ Jonrnal of Aprieultvre, Victoria. [10 Mat, 1916. 



RESULTS OF EXPERIMENTS, 1915. 



II. {ContiiLHtd from page 152). 



I.— LIGHT AND HEAVY DRESSINGS OF SUPERPHOSPHATE. 



A. E. V . Richardson, M.A., B.Sc, Agricultm'al Siiperintevdent. 



The question of the quantity of manure to apply per acre to a wheat 

 crop is of perennial interest to farmers. The seasonal conditions, 

 quality of soil, amount and distribution of rainfall during the growing 

 period and the methods of cultivation practised largely determine tne 

 actual amount. 



The majority of our wheat soils are naturally deficient in soluble 

 phosphates, and as the size of the crop is governed by the amount of the 

 most deficient plant food present, it follows that from a nutritive point 

 of view the amount of soluble phosphate in the soil is one of the limiting 

 factors in crop production. 



> ... . ., — 



View of Permanent Fertilizer Plots, State Research Farm, Werribee. 



Researches carried out in the chemical laboratory of this Depart- 

 ment during the past year show that immediately superphosphate is 

 applied to the soil it commences to revert into other forms. It changes 

 more or less rapidly into citrate soluble phosphate, and a small portion 

 becomes converted into insoluble phosphate. This process is called 

 reversion, and the rate at which it proceeds depends on the type of soil. 



Investigations have been conducted with typical wheat soils from 

 various parts of the State to find out, (1) the rate at which reversion 

 takes place with light and heavy dressings of super, and (2) the influence 

 of the nature of the soil on the rate of change. The results of these 

 investigations are approaching completion, and will be presented in due 

 course. Suffice it to say for the present that the tests show that more 

 than half of the water soluble phosphate in super, is reverted to citrate 

 soluble phosphate within a week of its application, and that within a 

 month practically the whole of the soluble phosphate is so converted. 



