40 The Rothamsted Wheat Experiments. 



wheat upon an acre of land, though furnished with an 

 abundance of minerals, and certainly at the commencement 

 containing more crop residue than the unmanured land, 

 has been able to obtain from the soil and the atmosphere 

 in excess of that in the wheat grown without manure ! 



The history of these plots 3 and 5 is very instructive. 

 Their yields year by year rarely differ from each other by 

 more than from 3 to 4 bushels per acre. The yield on both 

 is slowly declining, and for the last twenty-four years neither 

 has given as much as 20 bushels per acre ; and, without 

 some change in the manures, it is hardly likely this amount 

 can ever be grown again. The soil contains a large amount 

 of the mineral food of plants ; it also contains organic 

 nitrogen that is, nitrogen combined with carbon, the residue 

 of previous vegetation. This organic nitrogen is not directly 

 available as food for the wheat plant, but every year a certain 

 portion of it is converted into nitric acid, which combines 

 with the lime in the soil. In this state it is very soluble in 

 water, is readily washed out of the soil by heavy rain, and is 

 a most important and essential food of the wheat plant. 

 The amount of nitric acid formed each year will vary, the 

 process of nitrification being most rapid in the hottest weather, 

 provided the soil is sufficiently moist. The amount of nitric 

 acid which the wheat crop can take up will also vary, and in 

 a cold and wet winter much will be washed beyond the reach 

 of the roots of the plant. These facts are of universal 

 application, and by them it is possible to explain some of the 

 causes which tend to the production of good or bad crops of 

 wheat. Analysis proves both plots 3 and 5 to have lost a 

 large amount of organic nitrogen, and that, in the first nine 

 inches 1 depth, the mineral- manured soil has lost rather the 

 more. The total loss of nitrogen over a given area is larger 

 than the amount of that substance removed in the crops, 

 and the reason is that, except when the crop is in full vigour 

 of growth, the drainage waters contain nitric acid. Of the 

 281b. to 321b. of nitrogen per acre available each year at 



