KKFKCT. OE SUPEKPHOSPIi A'l'K < >N WHEAT YIELD, N.S.W. 9 



A comparison of the P^O 5 content with the known response to the 

 application of superphosphate is shown in the following table: 



TABLK V. Showing- comparison of P,O 5 content with response to application 



of Superphosphate. 



Though the number of soils investigated is comparatively small, there 

 is shown a relation between the responsiveness of the soil and the 

 contained amount of P.O.; that is to say, there is an analytical reason for 

 the variation in the responsiveness of the wheat soils to superphosphate. 



There is not a constant relation between the amount of total P,O- and the 

 amount of available P 2 O 3 present, and of the two determinations, as a 

 means of determining the responsiveness or otherwise of a soil, that of 

 the available P 2 O 3 would appear to be of greater value than the detrmina- 

 tion of the total P 2 O.. There are some striking instances of this in the 

 foregoing table. 



In the case of the Mungeribar soil in which the total P 2 O. would be 

 considered only "fair/' there is a notably high amount of available P,O S 

 present, which would indicate that there is not likely to be a response to 

 the application of superphosphate. Similarly in the case of the soils from 

 Quirindi and Delungra. 



On the other hand, Soil No. 6 from Tamworth shows a "satisfactory" 

 amount of total P,O 3 , while the amount of available P,O 5 is very low, and 

 would at once lead to the conclusion that the application of superphosphate 

 would prove beneficial. 



Further, although it is scarcely fair to try and arrive at a definite figure 

 from such a small number of soils, there are indications that the amount of 

 available P.,0- above which the application of superphosphate will not be 

 necessary, is somewhere between -0047 and -01 per cent. Dyer stated that 

 if the amount of available P 2 O.; fell below '01 per cent., a phosphatic fer- 

 tiliser would be beneficial. But it is possible that a lower figure should be 



