DAIRY AND SE£:D IMPROVEMENT MEETINGS. 375 



GYPSUM OR LAND PLASTER CANNOT TAKE THE PLACE OF 



CARBONATE OF LIME. 



In ordinary gypsum or land plaster, the lime is very largely 

 present in combination with sulphuric acid, on which account it 

 cannot correct the acidity of soils as slaked lime and ground lime- 

 stone do. In rare cases where the soil is naturally moist or 

 remains very wet for long periods of time, the sulphate of lime 

 in land plaster may be partially changed into calcium sulphide. 

 Later this may be changed by the carbonic acid in the soil or by 

 that brought down in the rain water, into carbonate of lime. 

 In this case the sulphur escapes into the air in combination with 

 hydrogen in a gaseous form. After these changes the residual 

 carbonate of lime would have a tendency to lessen the acidity 

 of the soil. Superphosphates and complete fertilizers which 

 contain sulphate of lime may, under similar conditions, have the 

 same effect. 



AMOUNTS OF LIME TO APPLY. 



In very rare instances, as, for example, in the case of heavy 

 soils which are excessively rich in aciS organic matter, which 

 yield black extracts upon treatment with ammonia water, and 

 which redden blue litmus paper, quickly and intensely, from 

 four to five tons of ground limestone may be required to the 

 acre. On soils which are moderately acid, and which contain 

 less organic matter, from two to three tons are usually sufficient. 

 In general, two tons to the acre will correct the condition of most 

 New England soils sufficiently for the satisfactory growth of 

 most ordinary farm crops. 



If a soil is exceedingly light, sandy or gravelly, and is deficient 

 in organic matter, a ton to one and a half tons of ground lime- 

 stone will sometimes answer for the present. In the case of 

 those heavy clay soils which bake badly, and which are rich in 

 vegetable matter, one may apply as high as from two to three 

 tons of slaked lime to the acre or from one and a half to two 

 tons of finely ground, burned lime. Owing to the caustic effects 

 of burned and slaked lime, on account of which it is more 

 destructive to organic matter, and more likely to cause injury to 

 crops the first season, finely ground limestone is usually pre- 

 ferred, for all ordinary soils. 



