MAINTAINING SOIL FERTILITY 283 



The chemists give us indisputable proof that even 

 a soil that has become so "poor" that it hardly 

 pays to crop it, is likely to have stored within it tons 

 upon tons of plant food; that it is in no way ex- 

 hausted, as we have been taught to believe. Yet 

 the fact remains that this same soil will not pro- 

 duce large crops. What, then, is the trouble ? 



Plant Food Locked Up. Much of the tons of 

 plant food that the chemist finds in ordinary farm 

 soils, is "locked up", or unavailable, from two 

 causes. In the first place it may not be in the right 

 form for plants to use, it may be in a compound 

 that is distasteful to the plants; or it may be in a 

 form that is not soluble in soil water, so that it 

 cannot be absorbed by the roots. Plants accept 

 food only when it is in a certain form. The chem- 

 ist, however, cannot tell how much of the total 

 amount of nitrogen, potash and phosphoric acid 

 that he finds in soil is in such shape that plants can 

 use it. He cannot determine with any degree of 

 certainty what proportion of the 4,000 Ibs. of ni- 

 trogen, 6,000 IDS. of phosphoric acid and 20,000 

 Ibs of potash that are in an acre of average farm 

 soil is in the right form for crops to use. There 

 is no way of finding out this very important point 

 except to grow plants upon the soil. 



Poor Texture* a Cause of Infertility. Part of 

 this great amount of plant food that is found in all 

 ordinary farm soils may have been made useless to 

 crops, for the time being, by poor texture, lack of 

 warmth and poor drainage. 



Mere richness in plant food avails nothing if 

 there is not enough water to make a very large 

 quantity of a weak solution of that food for the roots 

 to absorb. The arid lands of the West are very 

 rich in plant food, but are valueless for cropping 



