Compensation for Unexhausted Manurial Values. 113 
possible, a similar scale for the assessment of the unexhausted 
value of such Fertilisers as are generally used on a farm/ and 
to indicate what might be expected to be the period of duration 
of these, and how much of the original value is left after 
the taking of one or more crops. This we have found to be 
by no means an easy matter. In the first place, reliable sources 
of information are but few in number. Then, it is well-known 
that different fertilisers act very differently according to the 
nature of the land to which they are applied. Thirdly, there 
are the differences attaching to the growing of different crops, 
for these will not all alike remove the same constituents, nor to 
the same extent. The influence of manures must depend, not 
only upon the suitability of them for the particular purpose for 
which they are employed, but also upon the condition of the 
land, and whether they have been rightly applied. Hence, to 
draw up a set of Tables attempting to provide for all cases that 
might occur, for all classes of land, for all variations of cropping 
and rotation, would involve such complication as to render 
them practically useless. 
The most we have been able to do is, after a cousideration 
of such data as exist, and of what is known generally regarding 
the action of different fertilisers, to. draw up a general Table 
which, at least, will have the merit of being an approximation 
to the truth, and certainly be better than many of the hap- 
hazard and variable systems of valuation at present adopted. 
We have, however, seen it well to discriminate between the 
application of fertilisers to arable land and grass land re- 
spectively. Where, as in the latter case, there is always a crop 
on the land, the constituents of manure are more fully retained 
and do not drain away so readily as on arable land. 
Thus, we have allowed, in the case of grass land, compen- 
sation to extend over a longer period than with arable land. 
Notably is this the case with such materials as basic slag and 
lime, the influence of which is known practically to last longer 
on grass land. 
Though one crop, say for example, a cereal crop, will not 
take as much out of the land as does a root crop or a potato 
crop, it is impossible to discriminate between the residues each 
Avould leave behind. The decisive factor is less the with- 
drawal by the crop than the changes which afterwards go on 
in the soil. 
Between different classes of soil, also, we have not been able 
to discriminate, but must leave it to the discretion of the 
valuer whether the manures have been rightly applied or not. 
This is more especially the case when manure has been put on 
grass land, e.g. in cases such as those of superphosphate, bones, 
basic slag, and lime. Superphosphate, for example, is in some 
