Summary of Results. 59 



facts. An unmanured soil has yielded forty successive crops, 

 averaging 14 bushels per acre, solely by means of its existing 

 fertility. At the outset the soil contained a large amount of 

 organic nitrogen, derived from previous vegetation ; it like- 

 wise contained a large amount of mineral food. Every 

 year a portion of the organic nitrogen has been nitrified by 

 the agency of organisms living in the soil ; part of the 

 resulting nitrates has contributed to the growth of the 

 wheat crop, and part has been washed out of the soil or other- 

 wise lost. This loss of nitric acid is greater in wet seasons, 

 and the amount taken up by the wheat crop is consequently 

 smaller ; so that comparatively dry seasons should be favour- 

 able to the production of large wheat crops. The stock of 

 soil fertility in the form of organic nitrogen has been 

 considerably reduced, and the stock of both potash and 

 phosphoric acid has likewise been largely reduced. Never- 

 theless, the stock of fertility that remains would appear to 

 be sufficient to grow crops of wheat for a very long period, 

 though the produce must necessarily lessen in course of 

 time. 



With regard to manures, minerals alone have added very 

 slightly to the unmanured produce, whereas manures con- 

 taining nitric acid alone, or some easily nitrifiable compound 

 of nitrogen, have considerably increased the crop ; hence the 

 soil had a stock of minerals which the crop was unable to 

 utilise, on account of the insufficient supply of available 

 nitrogen. Manures consisting of potash, phosphoric acid, and 

 nitrogen (as ammonia-salts, or as nitrates), appear competent 

 to grow large crops of wheat continuously. In the ordinary 

 course of agriculture with rotation, as practised in this 

 country, the supply of mineral constituents immediately 

 available for the wheat crop is almost invariably in excess, 

 relatively, to the immediately available supply of nitrogen 

 from the atmosphere, or the accumulated stores within the 

 soil itself. Furthermore, with few exceptions, the worse the 

 so-called " condition " of the land that is, the more it is in 



