SCIENTIFIC AGRICULTURE. 203 



pounds per acre, cither in solution or in powder just before a 

 rain. [It must not be inferred, that this, or any other manure, 

 because it is recommended for a particular species of plants, is 

 not therefore adapted to the growth of others; but those only 

 are mentioned, upon which they have been tried sufficiently to 

 warrant a conclusion as to their efficacy.] 



Sulphate of magnesia, or epsom salts, is said to be useful to 

 young crops of wheat, clover, peas and beans: one or two 

 hundred pounds to an acre should be used. 



Sulphate of lime, or gypsum. This salt of lime, usually 

 called "plaster," has been long known and much employed as 

 a fertilizer on almost all crops and soils. It requires much 

 water for its solution. The beneficial operation of gypsum is 

 supposed to depend upon several circumstances. This, like all 

 the sulphates, furnishes sulphur, which is important in the 

 nutrition of plants, especially those of the liguminous order. 

 Gypsum prevents the escape of ammonia which is deposited 

 in the soil by rain, and evolved by the decomposition of ani- 

 mal and vegetable matters. In soils deficient in lime, it supplies 

 this element in an available state for their nutrition. It has 

 been thought to operate most beneficially on red clover and 

 Indian corn. 



Nitrate of soda is on some accounts a good fertilizer; it has 

 not come into general use, and is not as well understood in its 

 relations to soils and to plants as it should be. Several results 

 are theoretically attributed by Johnston to the action of the 

 nitrates on vegetation. 1. They give a dark green color to 

 the leaves. 2. They hasten and sometimes prolong the growth 

 of vegetation. 3. They increase both the straw and the grain 

 of the cereals. 4. They impart a saline taste to hay and 

 straw, which causes cattle to eat them with more avidity. 

 5. Grain which has been manured with the nitrates yields 

 more bran and less flour than those manured with other salts 

 The nitrates increase the oat crop ; they should not, however, 



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