484 INVESTIGATION BY CULTURE EXPERIMENTS 



The primary object in applying lime is to correct soil acidity. 

 In the spring of 1902 one ton per acre of slacked lime was applied; 

 but, a method having been worked out by which it can be deter- 

 mined by chemical analysis how much lime is equivalent to the 

 soil acidity to any depth, it was found that the soil on this field 

 was acid in the surface, more acid in the subsurface, and still more 

 acid in the subsoil ; and in order to provide ample lime to correct 

 this acidity, an additional application of eight tons per acre of 

 ground limestone was made in the fall of 1902. From all informa- 

 tion now available, it is believed that two to five tons per acre of 

 ground limestone as an initial application will give very satisfac- 

 tory results. Heavier applications may give more profit per acre, 

 but less profit per ton of limestone used. 



Phosphorus has been applied at the rate of 25 pounds, and po- 

 tassium at the rate of 42 pounds, per acre per annum, the present 

 regular practice being to apply once in three years 600 pounds of 

 steamed bone meal, containing ii\ per cent phosphorus, and 300 

 pounds of potassium sulfate, containing 42 per cent of potassium. 



Seven crops of corn, six of wheat, one crop of oats, and six of 

 cowpeas and one of clover have been grown on the field since the 

 work was begun in 1902. The yields of corn, oats, and wheat are 

 given in Table 97. 



Counting only the crops removed, the limestone, at $1.50 per 

 ton, has paid for itself and left a net profit of 34 per cent; and, 

 assuming 1000 pounds' loss per acre per annum, more than half of 

 the application still remains in the soil. Neither phosphorus nor 

 potassium has been used with profit, but it is interesting to note 

 that plot 5 has produced six times as much wheat as No. i. 



Seasonal conditions have very markedly influenced the yields of 

 crops. Larger use of crop residues to increase the organic matter 

 of the soil promises further improvement. 



Some very instructive results have been obtained from a series of 

 pot-culture experiments which have been in progress since 1902 

 in the pot-culture greenhouse of the Illinois Experiment Station, 

 and in which this yellow silt loam of the unglaciated hill land has 

 been used. The soil was collected in the fall of 1901, and represents 

 the old worn hill soil of Pulaski County, Illinois, only a few miles 

 from Kentucky. It is much poorer in nitrogen and humus than the 



