MANURES FOR THE WHEAT CROP. 75 



are, indeed, not large, and its price is high. Still it would 

 be a very economical manure if it increased the immediate 

 produce by an amount containing anything like the pro- 

 portion of that supplied, which is obtained in the case of 

 nitrogen, when nitrogenous manures are employed. But 

 current practices have certainly not yet so far reduced the 

 relative supply of potass in our soils, as to render the ap- 

 plication of direct potass manures to the wheat crop at all 

 profitable to the farmer. The results detailed in this paper 

 clearly show, however, that salts of potass are effective 

 enough on the growth of wheat when the immediately 

 available supply within the soil is really unduly exhausted 

 relatively to that of other mineral constituents, provided 

 only that there be no deficiency of available nitrogen. In 

 the case of leguminous crops, indeed, potass manures will 

 frequently greatly increase the amount of nitrogen assim- 

 ilated over a given area, without any direct supply of the 

 latter by manure. And should it happen that our modern 

 system of town drainage should lead to such an exhaustion 

 of our arable lands of their due proportion of available 

 potass, that potass manures from without should become 

 really effective, there can be little doubt that a sufficient eco- 

 nomical source of supply would soon supervene on such a 

 demand. 



" There is, of course, no question that if the manurial 

 constituents resulting from the consumption of the corn and 

 meat sent into our towns could be returned to the land 

 whence they came, its produce would be considerably in- 

 creased ; for with the mineral constituents, there would 

 always be associated nitrogen, in amount which would serve 

 to render effective a considerable portion of all, if not the 

 whole of some, of those constituents. If, however, human 

 excretal matters continue to be diluted with water, to the 

 extent recognised by the growing system of urban defeca- 

 tion, and if dilute liquid sewage cannot be distributed in 

 small quantities over large areas at a much lower cost to 

 the farmer than has yet been proposed, there is little hope 

 that the manurial constituents derived from the human 



