KEVIEW OF PREVIOUS EXPERIMENTS 



REVIEW OF POT EXPERIMENTS WITH 

 INSOLUBLE PHOSPHATES 



IN order to ascertain with any degree of certainty the agricultural 

 value of a suggested fertiliser two types of experiments are necessary 

 pot experiments and field trials. Russell (23) discussing the relative 

 advantages of field and pot trials points out that as a general rule 

 pot experiments are more accurate than field trials. The experimental 

 conditions are more under control, and it is therefore possible to 

 bring out small differences between materials which it might not be 

 possible to secure under the conditions of a field trial. On the other 

 hand, the conditions under which pot experiments are conducted are 

 so artificial that a positive result is not always paralleled by a positive 

 result in the field. Furthermore, though very considerable difference 

 in the cropping power of the two materials may be shown by pot 

 experiments, it by no means follows that the differences will be 

 equally marked under field conditions. Whilst therefore pot experi- 

 ments are of great value as a preliminary method of investigation, 

 field experiments are always essential before any deductions can be 

 made relative to the economic importance of the factor under investi- 

 gation. If they are to be of real value such field experiments must 

 be carried out under varying climatic and soil conditions and on 

 different types of soil, and an attempt be made to interpret the 

 results in the light of such conditions. 



Dutton ( 6) during 1912 conducted a series of pot experiments designed 

 to ascertain the fertilising effect of that portion of the phosphoric 

 acid in basic slag which is not soluble in citric acid, and came to the 

 conclusion that such insoluble phosphate is active enough to feed a 

 short-lived plant like mustard. 



Bainbridge(2), in a paper on "The Effect of Fluorspar Additions on 

 the Phosphates in Basic Slag," describes a series of pot trials with 

 barley, and shows that a very insoluble fluorspar slag possessing a 

 citric solubility of only 6 %, when contrasted with a slag of 81 % 

 solubility, gives a yield of 61 % compared with the high soluble slag 

 yield of 100. These two experiments, although not conclusive, clearly 

 indicate that even short-lived crops such as mustard and barley are 

 capable of making considerable use of phosphates which are much 



