73 



[Senatr 



The matters taken from the soil, and their several proportions hav- 

 ing been ascertained, it seemed desirable to find the amount of eachy 

 which a medium crop of each plant, subjected to analysis, would take 

 from an acre ; or how far a course of crops, such as is most approv- 

 ed, would exhaust the soil submitted to culture. In England, a fa- 

 vorite course is furneps, barley, clover and rye grass, wheat, called 

 the four years course ; and Prof. Johnston has given a table showing 

 the quantity of each part of the constituents of plants lost by the 

 earth during this course. He has also, in another place, shown what 

 would be the exhaustion from a three year's course of fallow, wheat 

 and oafs, as practiced in some parts of England, and in the table be- 

 low we have given the details of the first, and the results of the last. 

 Prof. Johnston estimates ^the crop of turneps at 25 tons, of hay at 

 one ton, and wheat at 25 bushels. The oats in the three year's 

 course he estimates at 50 bushels per acre. 



It will be observed, that in the first course a very large part of the 

 whole total, which is not far from 1000 lbs., is taken away by the 

 turnep crop. If it were required at the commencement of a four years' 

 course to supply the various inorganic or earthy substances that will 

 be taken from it, the following amounts, as calculated by Prof. John- 

 ston, would be applied. 



Dry pearlash, 325 lbs. 



Carbonate of soda, 333 " 



Common salt, 43 " 



Quick lime, 150 « 



