132 ELEMENTS OF AGRICULTURE 



This lacks 4,219 pounds of weighing ten tons, but it 

 has all the plant-food called for. One can put in this much 

 dirt for filler, but it would be simpler to merely use three- 

 fourths as much per acre as was planned. If such a fer- 

 tilizer were purchased ready-made, one would have to 

 pay freight on this much useless material. 



138. How to Determine What Fertilizer to Use. Grass 

 crops and most crops whose yield depends on the total 

 vegetative growth, are more likely to need nitrogen than 

 are ordinary crops. On the Cornell University farms, 

 fertilizers gave little benefit when used on oats, corn or 

 wheat, but, when nitrate of soda was applied on timothy, 

 it increased the yield from one and one-half to three and 

 three-fourths tons per acre. (See Fig. 55.) 



Leguminous crops are more likely to need phosphoric 

 acid, potash and lime than are other crops. (See Fig. 97.) 



If lime is needed, phosphoric acid is also very likely 

 to be needed, because most of the available phosphorus 

 is in combination with lime. There may, however, be plenty 

 of lime and not enough phosphorus, for the great store- 

 house of lime is limastone. 



In a general way we may say that nitrogen promotes 

 leafiness, while phosphoric acid and potash have more 

 to do with seed-production. This may help in determin- 

 ing what fertilizer to try, but must not be relied upon too 

 much. 



More important than any of these points is the value 

 of the crop. High-priced crops may be profitably ferti- 

 lized when it would be folly to fertilize low-priced ones. 

 A truck crop may be worth $200 per acre on the same farm 

 where a corn crop is worth $20. If a certain fertilizer 



