PLANT FOOD 



85 



The quantity of minerals drained from powdered 

 glass indicate an elementary rule important in 

 agriculture ; it was found that three per cent of the 

 glass dissolved in the percolating water ; of course, 

 the particles were microscopically fine. This dem- 

 onstration gave reasons for the importance of tillage 

 to every farmer in the land, promoting the wide- 

 spread opinion among modern horticulturists that 

 the maintenance of fertility is largely a matter of 

 providing soil moisture where needed. The inter- 

 esting revelation soon followed the above that as 

 roots absorb minerals from this solution its strength 

 is revived by additions from the same soil particles, 

 so that with constant water supply the proportion 

 of plant food remains about the same. Ordinarily, 

 soil minerals resolve at least as readily as powdered 

 glass. 



By laying aside our traditions about fertility 

 common illustrations of these facts can be recalled. 

 One man raises potatoes on the same piece of 

 ground year after year, the annual crop decreasing 

 until too small for profit. He terms the ground 

 "worn out" and leaves it idle for a year, or more, 

 to recover vitality. While unused no mineral plant 

 food is added ; it is simply idle land, and yet. after 

 a while, will grow potatoes again. Then there was 

 always a sufficient quantity of potash and phos- 

 phorus. If the farmer had added fertilizers during 

 the years crops declined he would have postponed 

 the time when yields ceased, but the soil would 



