GETTING ACQUAINTED WITH PLANT FOOD 



73 



The gap between laboratory and field tests. No one 



realized these discrepancies more quickly than the early 

 investigators themselves. But they could not explain 

 them. They felt they were working in the right direction, 

 but the results of the laboratory and those of the field 

 often failed to find a common meeting point; often the 

 laboratory results indicated high producing qualities, but 



POOR GRASS, POOR CATTLE 

 This soil is deficient in available plant food and humus 



the actual field results showed decided negative results ; 

 often the laboratory results indicated only mediocre crops, 

 yet at harvest time the fields showed entirely opposite 

 results full crops, as good as the best. 



The explanation is here. In more recent years an ex- 

 planation has been suggested. It is this: Kvery soil con- 

 tains two kinds of plant food: usable, such as plants 



