SELF-MAINTAINING FERTILITY 215 



tions, then use, apply them, and reap bounteous 

 rewards. 



PLANT FOOD THAT NEVER RUNS OUT 



In a general way we can say that fertilizers 

 furnish nutriment for plants, just as does food 

 for people. There is a certain, or rather, varying 

 amount of plant food at all times in nearly all 

 soils, just as each house contains more or less pro- 

 visions; or to make the simile more accurate, just 

 as a gardener has some potential food in his growing 

 vegetables. They, however, take time to ripen 

 and become edible; so, too, the plant food in the 

 soil needs time in which to become available for 

 the plants. Hence while the housekeeper saves 

 time by furnishing the family with purchased steak, 

 condensed milk, soups etc., the gardener supplies 

 plants with rapidly soluble fertilizers, liquid manure, 

 etc. For, you must know that plants obtain all 

 their food in the form of solutions, the dissolving 

 agent being the moisture in the soil. 



We can go a step farther in the comparison. 

 The unavailable material in the soil must be changed 

 and prepared for assimilation by the plants; the 

 raw, unprepared food in the kitchen must be cooked, 

 mixed and prepared for the table. In the kitchen 

 are cooks who do this work; in the soil are bacteria 

 or "microbes" which do the same thing with the 

 plants' "uncooked" provisions. 



Of these "soil cooks" there are several general 

 groups. The first accomplishes what is called nitri- 

 fication, the breaking down of complex combina- 



