EXPERIMENTS OX THE MIXED HERBAGE OF PERMANENT MEADOW. 319 
If we assume, for the sake of illustration, that the potass artificially supplied was the 
most readily available, and that the crop relied entirely upon it so long as it lasted, 
the result would be that only about 376 of the 900 lbs. applied, remained as residue 
after the first six years, and that nearly the whole of this was taken out during the 
next seven years. That it was not all recovered by that time would appear from the 
fact that in every one of the following seven years there was still considerably more 
potass in the crop of plot 8 than in that without manure. 
If, on the other hand, we suppose that the soil yielded up as much potass from its 
own stores to the crop of plot 8 as to that without manure, there would remain at the 
end of the six years of the application 567 lbs., or nearly two-thirds of the whole 
supplied still to be accounted for. On the same supposition, at the end of the next 14 
years there would still remain more than 300 lbs. of the supplied potass as yet 
unaccounted for. That some did, and does still, remain in an available condition may 
be concluded from the fact that there was a considerable excess of produce, of mineral 
matter, and of potass, removed from plot 8 compared with plot 3 in the two succeeding 
years, 1876 and 1877, and there was again an excess of produce in 1878. 
Whether, however, the soil did actually yield up from its own resources more or less 
to this manured than to the unmanured produce, we have not the means of determin¬ 
ing. It has been seen that the superphosphate of lime applied alone on plot 4-1 
enabled the herbage to take up very little more potass from the soil. But in that case 
there was extremely little increased growth. On plot 8, on the other hand, there was, 
besides superphosphate, the residue of potass previously applied, an annual supply of 
sulphates of soda and magnesia also, and with these considerably increased luxuriance 
of growth. Under such conditions the roots of the herbage would doubtless have 
possession of an increased range of soil and subsoil, and as it is obvious that notwith¬ 
standing the considerable residue of previously supplied potass the growing plants 
nevertheless suffered from a deficient available supply of it relatively to other con¬ 
stituents, it would appear probable that they would extract from the soil, at any rate 
as much as the unmanured herbage. Our knowledge, or rather our ignorance, of the 
condition in which the available portion of the potass of the soil itself exists within it, 
and is taken up by the roots, or of the condition in which the unexhausted residue of 
the previously supplied potass is retained, and becomes available in so piece-meal a 
manner, is such that it is impossible to come to any definite conclusion on the point. 
It will be seen that the facts suggest an interesting and useful line of experimental 
enquiry. 
That certain soils do, as a matter of fact, retain a residue of supplied potass, and in a 
slowly available condition, for very many years, is conclusively proved by evidence of 
very different kinds. Thus, in the experiments at Uothamsted in which wheat has 
now been grown for 36 years in succession on the same land, the effects of the residue 
of potass supplied more than 28 years ago are still traceable in an increased produce 
compared with that where there had not been such supply, and also in an increased 
