SOIIy DEFICIENCIES 



255 



to have a certain ratio to magnesia. An excess of either lime or 

 magnesia is not desirable. 



Lime Compounds in the Soil. Lime is found in the soil as the 

 carbonate, sulphate, humate, and various more or less complex 

 silicates. Calcareous soils contain considerable amounts of car- 

 bonate of lime. It is quite probable that some soils rich in humus 

 contain fair amounts of calcium humates. As a rule, the lime 

 is present in the form of silicates, which are more or less resist- 

 ant to the action of acid and weathering agencies. 



Fig. 62. Distributing lime. Ohio Station. 



Application of Lime. 1 Lime is applied to the soil as (a) Land 

 plaster or gypsum, CaSO 4 2H 2 O which has no power to counter- 

 act acidity; (b) Quicklime CaO, which is the most active form of 

 lime. It is usually slacked before it is worked into the soil. It 

 soon takes up carbon dioxide, and changes into the carbonate. 

 It is made by heating the carbonate, and so is often called burned 

 1 Bulletin 159, Ohio Station ; Wheeler, Farmers Bulletin No. 77. 



