LECTURES AND ESSAYS. 



407 



greatest profit? Are larger yields a remedy for lower prices? These are live 

 questions in agricultural science and in farming practice. 



Fortunately the experiments of Lawes and Gilbert with different fertilizers 

 in different amounts, upon wheat, in permanent plats, were continued for 

 sufficient time to furnish reliable facts upon the action of different amounts 

 of the same manure. These experiments have been in progress for more 

 than forty years, but in the later years some of the heaviest applications 

 were discontinued, and this paper will consider only the first twenty years. 



These experimenters soon learned that upon wheat mineral manures alone 

 had little effect, and that some form of combined nitrogen is the active 

 agent in increasing the yield. Ammonia salts were employed for that pur- 

 pose and in greatly different amounts upon different plats. Wheat was 

 sown each year upon each plat, and the treatment of a plat once begun was 

 unchanged throughout the experiment. For the present purpose but a few 

 of their many plats will be considered, and the numbers employed are here 

 used only for convenience of reference. These plats are the only ones so 

 treated, and these particular ones are chosen as being the only ones illustra- 

 tive of the principle under consideration. Hence the conclusions drawn 

 are fairly taken and are in no sense " sought for." 



These plats were annually treated for twenty consecutive years, as shown 

 in the following table, which gives the average yield of each plat, omitting 

 the first eight years, that the differences may be due solely to treatment. 

 Hence the figures are for twelve seasons after eight years' preliminary treat- 

 ment. 



Table Compiled from Wheat Experiments of Lawes and Gilbert. 



The above results are represented graphically in the following diagram 

 by the line marked C D, while the line A B shows the results of the same 

 experiment for forty years, that is twenty years longer. This lower line and 

 the yields for the forty years are given only for comparison. In the diagram 

 each vertical space represents one bushel average annual yield, and attention 

 is directed to the upper line — the yields for twenty years. 



Diagram No. 1, showing yield per acre of different plats: 



