210 SOILS AND FERTILIZERS 



crop should be that which experience has shown to 

 be the best. On one wheat, and one corn plot, 8 

 pounds of nitrate of soda should be used, a plot each 

 of wheat and corn being left unfertilized. If both the 

 corn and the wheat are benefited by the application 

 of nitrogen, the soil is in need of available nitrogen. 

 If, however, the wheat responds and the corn does not, 

 the soil is not in great need of nitrogen but does not 

 contain an abundance in available forms. 



284. Deficiency of Phosphoric Acid. In experi- 

 menting with phosphoric acid, turnips are grown on 

 two plots and barley on two plots. To one plot of 

 each 1 6 pounds of acid phosphate are applied. If 

 both crops show marked additional yields the soil is 

 in need of available phorphoric acid. If only the 

 turnips respond while the barley is indifferent, the soil 

 contains a fair amount of available phosphoric acid. 

 Barley and turnips are used because there is such a 

 marked difference in the power of each to assimilate 

 phosphoric acid. 



285. Deficiency of Potash, In order to determine 

 the condition of the soil as to potash, potatoes and 

 oats may be used as the trial crops, and 8 pounds of 

 sulphate of potash should be applied to one plot of each. 

 Marked additional yields indicate a poverty of availa- 

 ble potash ; an increased potato crop and an indiffer- 

 ent oat crop indicate potash not in the most available 

 forms. If no additional yields are obtained from 

 either crop the soil is not in need of potash. 



