270 Fertilizers 



nitrogen from the air depends largely upon the supply 

 at their command of the mineral elements, phosphoric acid, 

 potash and lime ; the presence of these is of primary im- 

 portance, and good crops cannot be grown on land deficient 

 in these elements. In any event, therefore, liberal supplies 

 of the minerals should be provided, in order that maximum 

 yields may be obtained. (See Fig. 24, Plate XI.) On soils 

 of medium fertility which are fairly well supplied with 

 vegetable matter, the need for nitrogen is not marked, 

 even in the early growth of the plant. On lighter soils, 

 however, a nitrogenous fertilization is often serviceable, 

 because supplying nitrogen before the plant has acquired 

 the power of obtaining it from the air. This practice 

 enables the plant to make an early start, and prevents 

 the delay in growth which sometimes occurs, particularly 

 on light soils, during the period immediately after germina- 

 tion, when the plant is unable to obtain its nitrogen from 

 sources other than the soil. A green forage crop averaging 

 10 tons to the acre requires, on the average, about 30 

 pounds of phosphoric acid and 100 of potash, and the 

 nitrogen which necessarily accompanies these amounts 

 of minerals will reach, on the average, 100 pounds. If 

 this element is drawn from the air, because provided with 

 an abundance of minerals, it is manifestly economy to 

 supply the full amount of these required, rather than 

 omit them, and thus to limit the plant's power of acquiring 

 this expensive element, since the value of the 100 pounds 

 of nitrogen gained is greater than the cost of both the 

 phosphoric acid and potash required. The fertilization 

 of these various clovers may be much the same; in 

 general an application of 200 pounds of acid phosphate 

 and 100 of muriate of potash should be sufficient, espe- 

 cially if they follow a well-fertilized crop, such as potatoes. 



