100 
CORRESPONDENCE. 
ECOLOGICAL METHODS OF SOIL ANALYSIS. 
With regard to the recent discussion on this subject (see The Naturalist, 
1013, pp. 169, 239, 436), there is perhaps something to be said, on grounds 
of linguistic accuracy, for insisting that the ‘ content ’ of the soil in any 
constituent, when expressed as a percentage, should be related to the 
sum-total of all the constituents taken as 100, rather than to any other 
standard. But it is certainly true that in the case of water, which stands 
in quite a special position as a soil constituent, many investigators have 
expressed the content as a percentage of ‘ air-dry ’ soil or of soil dried 
at ioo° C., and provided the fact is stated, no one is misled. Similarly 
with regard to ‘ water absorbed.’ If we start with, we will sav, ‘ air-dry ’ 
soil, and make it absorb water till it is saturated, it is perhaps most natural 
to relate the amount of water absorbed to the weight of the air-dry soil, 
because that is what one started with, just as in the case of analysing 
a moist soil, it is the whole weight of this with which one starts. Thus 
we have a technical difference established between ' water absorbed ’ 
by a dry soil (related to the dry soil) and ‘ water content ’ of a wet soil 
(related to the wet soil).* Mr. Crump, however, was not dealing with 
water absorption experiments but with water contents of natural soils, 
and if he finds it more illuminating to relate the said water contents to 
the dry rather than to the wet soils, surely it is just a trifle pedantic 
to lay all the stress on the technical point, where, if Mr. Crump errs, 
he errs in very good company, while ignoring without a word of comment 
the advantages Mr. Crump claims for his procedure. 
With regard to taking the water-content as loss on air-drying rather 
than as loss at 100 C., there is difference of opinion as to which method 
is preferable, and there is at least something to be said on both sides. 
Into this question it is not my purpose to enter. Again, Mr. Johnson is 
right that there cannot in the strict sense be two water contents of 
the same soil, but if exactly what is meant is made clear there can be no 
quarrel on the ground of ‘ confusion ' ; at the most exception may be 
taken to the particular use of terms. 
Mr. Johnson is very anxious about ‘ adding another to the already 
too long list of standards.’ Has he not realized that scientific progress 
largely consists in readjusting our standards as we discover new relations 
between phenomena ? Mr. Crump’s ratio, or ’ soil-moisture co- 
efficient ’ is precisely an attempt in this direction, and it promises, I 
think, to be a very valuable attempt. The fact that Mr. Crump has 
actually obtained strikingly concordant results* where hitherto we have 
groped among strikingly discordant ones is in itself sufficient proof of the 
value of his new method. 
In dealing with Mr. Crump’s ratio, Mr. Johnson says that 
this ratio, ‘the “convenient method ’ given for estimating the humus 
content ’ is ‘ obviously incorrect,’ and goes on to allude to ‘ this equation.’ 
Mr. Crump gives no such equation and alludes to no such equation. 
The ratio in question is stated by Mr. Crump to be a ‘ convenient way 
of expressing the humus content of the peat.’ Mr. Johnson substitutes 
for ‘ expressing ’ the word ‘ estimating ’ in one place and ‘ obtaining ’ 
in another, and ‘ gives ’ in a third. He has no difficulty in showing that 
you cannot ‘ obtain ’ a quantity by means of a ratio one of the terms of 
which is the quantity itself, or in other words, that -- > - tl - ll - s , - humus 
1 - mineral 
is an absurd equation. But Mr. Crump’s word was ‘ express,’ which has 
a distinctly different meaning. The ratio in question gives, of course, 
Naturalist, June 1918, p. 241. 
I See the original abstract now reprinted in the Journal of Ecology s Vol. I., p. 9f>, and 
especially New Phytologist, Vol. XII.. 1913, pp. 125-147. 
Naturalist, 
