Feeding the Land 



205 



While the grower is feeding the soil, the crops 



are taking many tons of ingredients from it in the 

 form of straw, — that is humus, growth of wood, 

 twig, branch, and vine, leaf, stalk, and flower; 

 potash, nitrogen, and phosphoric acid. The amount 

 of material thus actually abstracted by the 



Commercial Phosphoric Acid Fertilizers: Composition of Fertilizer 

 Materials Used as Sources of Phosphoric Acid : 



The Nitrogen Fertilizers: Composition of Fertilizer Materials Used 

 as Sources of Nitrogen : 



