223 Bureau of Farmers' Institutes. 



moistened with water, when it will retain the ammonia which 

 would otherwise escape. For the same reason, plaster is useful 

 to distribute about stables, so that it may mix with the manure. 



2. It has been shown that gypsum in sonic manner aids the 

 process of nitrification, by which ammonia and the nitrogen of 

 organic matter are converted into nitrate nitrogen. 



3. Gypsum acts upon the insoluble forms of potash and some 

 other elements of plant food, converting them into soluble and 

 available forms which plants can readily take up and use. This 

 is probably the most important effect of plaster as an indirect fer- 

 tilizer. 



In whatever way gypsum may act, it is well established that it 

 is of value when applied on certain soils to certain crops, such as 

 clover, peas, lucern and similar plants. Nearly all fertilizers 

 containing soluble phosphoric acid contain gypsum, as will be 

 explained later. 



The more common sources of supply of land-plaster are Nova 

 Scotia and central New York, the latter being less pure. 



Quicklime. — Quicklime or burnt lime or calcium oxide, com- 

 monly called lime, is known to be valuable as an indirect fer- 

 tilizer. It produces changes in both the physical and the chemical 

 character of soils. It changes the mechanical condition of soils 

 by loosening heavy clay soils and also by holding together and 

 giving body to light sandy soils. Freshly burned lime acts chemi- 

 cally upon soils by decomposing vegetable and mineral matter 

 already present in the soil and changing them into forms which 

 are available as food for the plant. Thus, lime acts upon in- 

 soluble mineral substances containing potash, soda, etc., and con- 

 verts them into soluble forms which plants can use. Lime aids 

 in the decomposition of animal and vegetable matter, such as 

 vegetable mold, stable manure, etc., and tends to convert them 

 into available plant food. Lime also neutralizes the acidity or 

 " sourness ,J of soils. We shall later consider the conditions 

 under which lime can be used to advantage and also the methods 

 of its use. 



Gas-Lime. — Quicklime is used in gas works for the purpose of 

 removing impurities from the gas. In the operation the lime 

 becomes slaked and lakes up various materials that are injurious 

 to plant life; however, these impurities, on exposure to air, arc 

 changed into harmless forms. In using gas-lime on soils, it should 

 either be exposed to the air some time previous to applying to soil 

 or should be applied some weeks or even months before putting 



