172 



COCOA 



CHAP. 



On heavy clay soils, however, the potash manure 

 may be omitted, as clay soils are always rich in potash ; 

 and when the chemical manures are given together 

 with farmyard manure, the above quantities should be 

 reduced. 



In carrying out manuring experiments a few "golden 

 rules " should be remembered : 



1. Always include in the series of plots a sufficient 

 number of unmanured " control plots," in order to be 

 able to compare the yields on manured and on un- 

 manured soil. 



2. Do not make the experiments on too small a 

 scale ; do not have the plots smaller than one acre each. 



3. Do not forget that the soil shows great variations 

 over a surface of several hundred acres ; therefore do 

 not draw general conclusions from a single series of 

 experiment plots at one place, but carry out experiments 

 at different places. 



4. Do not draw conclusions from the results of the 

 experiments after one year, but wait till the results of 

 some four or five years have been obtained. 



It is always a good thing to ascertain by a separate 

 series of experiments the effect of the addition of lime 

 to the soil. For this purpose the series of experiment 

 plots may be arranged as follows : 



Each plot should be one acre in size. 



In this connection, however, it must not be forgotten 

 that lime not only has the faculty of "sweetening" 

 sour soils, but also acts at the same time as a liberator 

 of plant -food, converting dormant plant -food into 

 available compounds. This faculty, though enriching 

 the soil temporarily, makes it poorer in the future, so 



