1867.] 



Presidenfs Address. 



177 



years in a systematic series of researches upon Agricultural Chemistry, vdth 

 a view of determining, by exact experiments, the principles, chemical and 

 physiological, which are involved in the general and fundamental processes 

 of successful agriculture. 



These investigations have embraced :— 



1. Researches into the exhaustion of soils, including experiments on 

 wheat, on barley, on turnips, on clover, and leguminous crops. 



2. Researches on the principles of rotation and fallow. 



3. On the mixed herbage of grass-land. 



4. On the process of vegetation generally, including researches upon the 

 action of manures. 



.5. On the origin of nitrogen in plants (Phil. Trans. 1861). 

 6. Researches on the feeding and fattening of animals (Phil. Trans. 

 1859). 



It is difficult to give in a short compass the practical conclusions arrived 

 at from a series of investigations upon a number of subjects each so com- 

 plicated in its nature, so important in its object, and continued systemati- 

 cally over so protracted a period. At the time your medallists commenced 

 their experiments it was generally supposed that certain saline bodies, or 

 so-called mineral constituents, were essential to the growth and develop- 

 ment of the plant, and that such substances must be furnished to it by the 

 soil. The necessity of a certain quantity of nitrogen was also recognized ; 

 but it was imagined, since wild plants could thrive without any artificial 

 supply of nitrogen, that a sufficient amount of this element existed in the 

 atmosphere (in the form chiefly of salts of ammonia) to render it unnecessary 

 to take any steps for increasing this supply ; and it was supposed that the 

 fertility of a soil might be maintained for an indeffiiite period if the different 

 mineral constituents carried off by the crop were annually returned in due 

 quantity as mineral manure to the soil. 



This mineral-ash theory, as it was termed, was proposed by Liebig ; but 

 it has been proved by Messrs. Lawes & Gilbert to be erroneous, as it em- 

 braces a part only of the truth. 



The field experiments upon which this conclusion rests were commenced 

 in 1843. Fourteen acres, divided into about twenty plots, were devoted to 

 experiments upon wheat, and seven acres, divided into about twenty-four 

 plots, to experiments upon turnips. Subsequently similar experiments were 

 made upon beans, clover, barley, and the mixed herbage of permanent 

 meadow-land. The general plan of the field experiments consisted in se- 

 lecting fields in a condition of agricultural exhaustion, that is, in a state in 

 which a fresh supply of manure was needed to fit the soil for the growth of 

 another crop. Upon this exhausted soil each of the most important crops 

 in the rotation were grown, year after year, upon the same spot, both with- 

 out manure and with many different descriptions of manure, each of which 

 was, as a rule, applied year after year to the same plot. By this means it 

 was possible to determine the point of relative exhaustion or excessive sup- 

 ply of any of the constituents of the manure. 



