496 Report of Experiments on the Groicth of Wheat. 
of cattle-foods, potass would be the most likely to become defi- 
cient. The sources of potass in the market 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 con- 
• taining anything like the proportion 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 application of direct potass-manures to the wheat crop at 
alj 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 avail- 
able 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 Legu- 
minous crops, indeed, potass-manures will frequently greatly 
increase the amount of nitrogen assimilated 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 propor- 
tion of available potass, that potass-manures from without should 
become really effective, there can be little doubt that a sufficient 
economical source of supply would soon supervene on such a 
demand. 
There is, of course, no question, that if the manurial consti- 
tuents 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 increased ; 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 
defecation, 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 food sent into our 
towns can be re-distributed over the area from which they came. 
Indeed, having regard to the inapplicability of dilute liquid 
sewage to arable land, except in small quantities and at particu- 
lar seasons, and to the assumed cost of distribution, it appears 
probable that the most profitable mode of utilisation of sewage 
will be, to limit the area by applying the greater part, if not the 
whole, to permanent or other grasses, laid down to take it the year 
round, trusting mainly to the periodically broken up rye-grass land, 
