LIME AND LIMING LAND 81 



a still further development of rotations of crops. Lime will never make poor 

 land rich if regarded simply as a manure, but, used aright, there is no means 

 available to the farmer that will more efficiently aid in the building up of 

 the productivity of his land. 



SULPHATE OF LIME, OR PLASTER. 



The sulphate of lime is a natural deposit found in certain sections, and 

 mined under the name of gypsum or plaster. Pure gypsum contains 32.5 

 per cent, of lime, 46.5 per cent, of sulphuric acid, and 21 per cent, of water. 

 It is frequently burned to form what is called plaster of Paris, which, when 

 mixed in water, rapidly hardens and is used for various purposes in the arts. 

 The pulverized rock, known as plaster, has been largely used as a soil applica- 

 tion. Like lime, the plaster has the power to release insoluble potash in the 

 soil, and it sometimes has a marked effect on soils containing a large percent- 

 age of potash. As in the case of lime, farmers seeing the effect that an appli- 

 cation of plaster has on their soil, have at times jumped to the conclusion 

 that plaster was all they needed to make their soil rich. But, as in the case 

 of lime, they have soon found that the continued application soon fails to 

 produce the effect that it once did, and that its continued use has so impover- 

 ished their soil that they have been compelled to resort to the commercial 

 fertilizers to restore the mineral constituents they have removed by their 

 short-sighted policy. 



While on some soils plaster has had this marked effect, there are other 

 soils on which the application of plaster has never had any marked effect. 

 Sandy soils near the coast, which are deficient in potash, seldom respond 

 favorably to the application of plaster. In an experiment made by the writer 

 a number of years ago, two fields adjoining in clover of the second spring 

 from sowing, were dressed with lime and plaster of the same money value. 

 Both made a handsome growth, but the effect of the freshly slaked lime was 

 decidedly more marked than that of the plaster, and the subsequent cropping 

 of the land showed that the limed field had collected far more nitrogen than 

 the one treated with plaster. 



A great deal has been said and written in regard to the use of plaster in 

 arresting the escape of ammonia from manure, and some seem to suppose that 

 dry plaster scattered about a stable will absorb ammonia and prevent its 

 loss. The fact is that plaster has little or no effect in preventing loss of am- 

 monia unless it is thoroughly mixed in the manure and moistened, for no 

 chemical recombination can take place in the absence of moisture. Plaster, 

 being the sulphate of lime, may, when well mixed with manure and moist- 



