i88 3 J 
An Unwelcome Truth. 
211 
IV. AN UNWELCOME TRUTH. 
By An Old Technologist. 
f OT very long ago the farmer was told by eminent 
agricultural chemists that he ought to know at all 
times what quantity of plant-food existed in his 
fields, so that he might at once see how much and what 
kind of manure need be added to meet the requirements of 
any crop intended to be planted. It was laid down that if 
the soils were carefully analysed at the outset, and if the 
weight and composition of the manures employed were 
added, and, on the other hand, the weight and composition 
of the crops taken from the fields year by year, a balance 
might be struck at the end of any season, showing how much 
combined nitrogen, phosphoric acid, potash, &c., remained 
on the soil. The whole affair had about it an appearance 
of beautiful simplicity. It was of course admitted that fer- 
tilising matters present in a soluble condition might be 
washed away in the drainage in a wet season. No one 
would have attempted to deny that ammonia, if present in 
the free state, or if combined with carbonic acid, must to 
some extent escape into the air. And it was also no secret 
that not all the mineral plant-food found in the soil, on 
chemical analysis, was present in an available condition. 
But the extent and importance of these drawbacks have 
only quite recently been placed before all concerned in a 
distinct light. 
It is only just to say that the results reached are un- 
pleasant and unwelcome. Still nothing can be gained by 
■ignoring fa( 5 Is, especially when they affedl the entire popu- 
lation of all civilised countries. 
It has been established, by the researches of M. P. P. 
Deherain, that — at least as far as combined nitrogen is con- 
cerned — the amount of plant-food removed from arable land 
by the crops is neither the whole, nor in many cases the 
greater part of the yearly loss. Given the original analysis 
of the soil, the weight and analysis of the manures added 
and of the harvests taken away, we cannot find the amount 
of plant-food remaining. An important factor has been left 
out of the account. 
M. Deherain began, in the year 1875, a series of experi- 
ments at the Agricultural Station at Grignon. The soil of 
