220 SOILS AND FERTILIZERS 



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 nitro- 

 gen, the soil is in need of available nitrogen. If, how- 

 ever, the wheat responds and the corn does not, the 

 soil is not in great need of nitrogen but does not con- 

 tain an abundance in available forms. 



281. 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 16 pounds of acid phosphate are applied. If both 

 crops show marked additional yields the soil is in need 

 of available phosphoric acid. If only the turnips re- 

 spond 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 phos- 

 phoric acid. 



282. 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 sul- 

 phate 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 the soil 

 is not in need of potash. 



