74 SOILS 



secure without difficulty, and unusable, such as is enclosed 

 in the storehouse of rocks and particles and compounds. 

 The soil analyst is not able to distinguish between these 

 two forms, with sufficient accuracy to tell exactly what 

 the plant may need at any given time. Neither his cru- 

 cible nor his acids will help him, in any certain degree. 

 When the test actually takes place in the field, the story 

 is there told with language of no uncertain meaning. In 

 a previous chapter the kinds of food were mentioned : 

 available, the not-immediately-available and the tight- 

 ly-secured plant food. 



Of course we cannot expect chemical analysis to show 

 the differences between these forms. We are able only 

 to determine the total amount of food present : the poten- 

 tial plant food, the food that is now and shall be available 

 some day hereafter, as food for plants. An old notion 

 is still held. " A great mass of people still believe, that all 

 that is necessary to know how to handle a soil is to secure 

 its analysis that the plant food content may be ascer- 

 tained. But, with our present knowledge, let this be 

 accepted as certainty : the chemist can determine only 

 the total quantity of plant food in the soil : the usable 

 plant food plus the unusable plant food. And he cannot 

 tell you whether it is available food or otherwise. It 

 will be necessary for you to seek elsewhere than the labo- 

 ratory for direction. 



Analysis will help to some extent. But an analysis 

 of the soil may do great good. It may indicate in what 

 direction improvement lies : whether tillage only is neces- 

 sary that dormant supplies may be called into use, 

 whether organic manures are best that the humus con- 

 tent may be increased, or whether mineral manures are 

 likely needed that they may reenforce the plant food al- 

 ready present. While it is true these are indicative only, 



