54 



EXPERIMENTS UPON WHEAT 



year period, 1844-1893, together with the nitrogen contained 

 in the soil at the close of that period for the unmanured Plot 

 3, and Plot 2 receiving farmyard manure. The top 9 inches of 

 soil only are considered, because the analyses do not indicate 

 that any appreciable amount of organic matter has found its 

 way into the subsoil. 



The results show that of about 10,000 Ib. of nitrogen supplied 

 as dung during the whole period, only about 2600 Ib. have 

 been recovered in the crop, or about 26 per pent., and that 

 although the nitrogen present in the soil at the end of the 

 period has been doubled, the excess over the manured plot is 

 only 2580 Ib. per acre ; so that there is still 5670 Ib. which 

 has been supplied in the manure, but is unaccounted for either 

 in the crop removed or in the accumulation in the soil : 



Some of this has no doubt been washed away as nitrate into the 

 drains and the subsoil water, some has been removed in the 

 weeds, but much must have been lost by the conversion, 

 through bacterial action, of nitrogenous compounds in the 

 manure into free nitrogen gas. 



Phosphoric acid and potash, however, behave very differ- 

 ently from nitrogen ; but little of these substances are ever found 

 in the drainage waters, and Dr Dyer's analyses show that the 

 greater part of the excess of phosphoric acid supplied over that 

 removed in the crop is still to be found in the top 9 inches of 

 soil, where it remains in a condition readily available for the 

 plant. The potash is not quite so completely retained as the 

 phosphoric acid, and descends further below the surface/ There 

 is still, however, no practical loss to be feared when potash is 



