10 



FARM ARITHMETIC. 



food. Good tillage, the addition of straw, stover, cotton- 

 seed, and stable manures, and the frequent growing of 

 clovers, alfalfa, cowpeas, and soy beans will increase the 

 quantity of plant food in the soil and will improve its 

 productiveness. Barnyard manure is one of the best of 

 all fertilizing materials. 



Buying plant food. The practice of purchasing plant 



Locked Up for Ages to Come 



All rock contains plant food. Nature releases but a small 



amount each year. All soil was originally rock. 



food— nitrogen, phosphoric acid and potash— in order to 

 supplement that already present in the soil has assumed 

 enormous proportions in recent years. These commercial 

 fertilizers are potential plant food, and are intended to 

 assist in supplying the needs of the growing plant, but 

 only in a small way. They are known as chemical 

 manures, or chemical fertilizers. 



