74 THE CULTURE OF FARM CROPS. 



This fact is full of significance to the farmer who may per- 

 ceive in it a proof of the necessity of a thorough pulverization 

 of the soil for the maximum growth and yield of his crops. 



Fifth. In the state of carbonate, in which it mostly ex- 

 ists, because of its affinity for this acid and the abundance 

 of it in the atmosphere ammonia decomposes gypsum 

 (sulphate of lime) and changes acids with it; forming sul- 

 phate of ammonia and carbonate of lime. This action only 

 goes on however when moisture is present. The beneficial 

 action of gypsum (the common agricultural "plaster") upon 

 clover, corn and other crops has been ascribed to this single 

 property. But popular impressions are easily formed and 

 take a firm hold upon the popular mind, which does not 

 stop to think and reason, or take pains and time to observe 

 closely ; hence the opinions thus formed are too often only 

 superficial and partial and are not substantial enough to 

 base a rule or principle upon. No doubt some of the favora- 

 ble results of an application of "plaster" to the soil, in some 

 cases, may be due to this mutual action of gypsum and car- 

 bonate of ammonia, or of gypsum and free ammonia upon 

 each other; but there are other principles involved in the 

 subject which must be referred to in a more appropriate 

 place hereafter and to which much of the effect of gypsum 

 is undoubtedly due. Nevertheless as it is a fact that gyp- 

 sum and carbonate of ammonia do exert this mutual reac- 

 tion upon each other, and under favorable circumstances 

 the result may be conspicuously marked upon the growth 

 of the crops. For 100 Ibs. of common finely ground gyp- 

 sum a comparatively small quantity to be spread over an 

 acre of land w r ill fix or unite with nearly 20 Ibs. of am- 

 monia, containing 16 J Ibs. of .nitrogen; a comparatively 

 large quantity of this scarce and invaluable plant food, for 

 it is equivalent to about 60 Ibs. of nitric acid and nearly 

 100 Ibs. of nitrate of soda, which is considered a very lib- 

 eral use of this most active fertilizer. And this fact is one 

 to be studiously considered and judiciously applied by every 

 intelligent farmer. 



Sixth. The presence of ammonia in a soil which contains 



