THE CHEMICAL PRINCIPLES OF THE ROTATION OF CROPS. 



PEONODWOED BEFORE THE AMERICAN AGRICULTURAL ASSOCIATION, MARCH 4th, 1846, BY 



D. P. GARDNER, M. D., 



HONORARY CONSTJLTING CHEMIST OP THE ASSOCIATION, iVTEMBER OF THE LYCEUM OF NATURAL HISTORY, ETC. 

 FORMERLY PROF. OP CHEMISTRY AND NATURAL PHILOSOPHY IN HAMPDEN SIDNEY COLLEGE, VA. 



Mr. President and Gentlemen : 



It is necessary to premise this memoir by explaining that the Executive Committee had 

 expected a communication from another gentleman and did not until a late hour throw the burden 

 upon me, but my desire to gratify them has induced me to hazard the criticisms of the Association — 

 tempered, as I know they will be — by the circumstances of the case. I have selected the subject of 

 the rotation of crops partly because opportmiities have fallen in my way to witness some facts which 

 are commonly overlooked by writers on this topic, and because I regard it as a question of pure 

 chemistry. I propose to search after general principles only, for if these can be determined, particular 

 cases or the rotation suited to any district of country will be determined by a little consideration. 

 This is moreover the only way whereby the subject can be discussed so as to be of utility to the 

 whole country, the agriculture of which it is the object of your association to advance. A local 

 rotation is hampered with considerations of expediency, with the price of land and of labor, the 

 merchantable crops, the profit or loss of grazing, which oifer obstructions to reaching any generaliza- 

 tion ; but whereas every crop and agricultural process is profitable in some part of our widely 

 extended coimtry, it is proper that such considerations should be dismissed, and introduced only in 

 reaching particular cases. I know that in this day practical disquisitions are considered superior to 

 all others, but if we make no effort to group facts scattered abmrdantly aroimd us, the ait can never 

 advance. Your Association has the noble object in view of reaching principles in agriculture, and 

 therefore I have no hesitation in presenting a theoretical memoir, the design of which is to attempt 

 the deduction of the principles of rotation. 



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