40 THE BOOK OF CORN 



important elements of plant food and one which must 

 be supplied to almost all soils, for all crops except 

 those of the leguminous family. 



Hydrogen — Hydrogen is a gas. It unites with 

 oxygen and forms water. It is useful to plants only 

 when combined with oxygen in the form of water. 

 Hydrogen is a very important factor in plant growth, 

 for the amount of water consumed by the growing 

 plant is enormous. For instance, as stated above, water 

 constitutes seventy-five per cent of many plants. The 

 amount of water, however, found in the growing plant, 

 is a very small proportion of the water required by 

 the plant during the entire period of its growth. That 

 this is true is proven by many experiments, which 

 show that from 300 to 500 pounds of water are 

 required by growing crops for every pound of the 

 dried crop. 



Phosphorus — This element unites with oxygen to 

 form phosphoric acid. When a base unites with this 

 acid, a salt is formed (phosphate) which is available 

 plant food. The amount of phosphorus required by 

 plants is not large, but the quantity found in most soik 

 is so limited that this element of fertility often limits 

 the productive capacity of many fields. In additicMi, 

 the phosphorus which is taken from the soil by 

 plants is largely stored in the seed or grain, and this 

 is often sold from the farm. For these reasons phos- 

 phorus is a very important element of fertility from 

 the farmer's standpoint. 



Potassium — This element forms with oxygen a 

 compound — potash, containing eighty-three per cent of 

 the element potassium. It is this compound which is 

 important in agriculture. Potash combines with an 

 acid to form a soluble salt which is taken up by the 

 roots of the plant. Some soils are deficient in potas 



