32 



The quantitative measurements give a much clearer picture 

 than was hitherto possible of the character of the soil population. 

 The average numbers obtained in the high activity period of 

 spring and the low activity period of the winter are as follows : — 



The weight (also the volume) of the protozoa in the soil 

 considerably exceeds that of the bacteria in spite of the high 

 numbers of the latter. 



It is more difficult to ascertain whether the production of 

 plant food fluctuates in the same way as the numbers of organ- 

 isms. There are undoubted fluctuations, but more data are 

 required before the proof becomes as rigid as it is for bacteria. 



There is definite evidence that crops obtain only part of the 

 possible food supply, much of the rest being taken by soil 

 organisms and thus rendered unavailable. One cannot as yet 

 say which are the worst offenders in this respect; at present 

 suspicion attaches to the algae, and the laborious task of clearing 

 up the problem is being carried out by Dr. Bristol Roach. 



CONTROL OF THE SOIL ORGANISMS. 



The knowledge of the soil organisms gained in our 

 laboratories is allowing of a steadily increasing degree of control. 

 There are at present four directions in* which large scale tests 

 are carried out. 



J. Inoculation of lucerne by the appropriate micro- 

 organisms. 

 2. Conversion of straw into a useful manure by the cellu- 

 lose decomposing organisms. 

 .'J. Control of the plant food production process by partial 



sterilisation methods. 

 1. Control of plant disease organisms by similar methods. 

 ()( these, inoculation has already been discussed on p. 



Artificial Farmyard Manur\e. — The production of manure 

 direct from straw is now being carried out on the large scale. In 

 the past season no less than 3,000 tons of straw and like material 

 were treated in Britain alone in addition to much larger quan- 

 tities treated abroad. 



The method of making artificial farmyard manure is based 

 on the facta thai the necessary organisms are already 

 present and need only suitable conditions to call forth their 



