Anonymous. IV – M. Liebig et l’agriculture en Angleterre et en Allemagne – Lois de la valeur des engrais. Journal d’Agriculture Pratique Vol 28:1 (1864, Jan-Jun), pp.117-120
(Article printed in issue of 2nd half of January)
This article shows that the “vegetable mould” story had crossed the Channel and was being reported in France as well. This editorial summarizes (and supports) the editorials that appeared in the Jan 2 and Jan 23 issues of the Gardeners’ Chronicle and Agricultural Gazette.
The final part of the article reports a lecture given to a meeting of the Highland and Agricultural Society of Scotland on Jan 20 given by Prof. Thomas Anderson, Chemist to the Society. Anderson’s work later appeared in Anderson, T. “Field experiments on the action of uric acid as a manure”. Transactions of the Highland and Agricultural Society of Scotland (New Series) (Jul 1863 – March 1865), pp.421-9 and pp.479-486. The work is of interest because it disproves Liebig’s assertion that it would be better to disregard the uric acid content of guano until it could be shown that it had nutritional value to plants. This might be thought of as proper scientific caution on Liebig’s part, but in fact an assumption of no value has just as many serious practical implications as an assumption of full value, as Anderson points out in his paper (p.422):
“The results of field experiments, when critically examined, seem to confirm this view [that the total nitrogen content of a manure can be used to judge its nitrogen-giving qualities], and it has, therefore, been customary for many years to reckon the whole of the nitrogen in any manure as if it were ammonia; and I am not aware that any practical difficulty or error has resulted from this course. The question, however, has been recently again opened up by Liebig; and in discussing the manurial value of Peruvian guano, he has particularly insisted on the well-known fact that part of its nitrogen exists as ammonia, and part as uric acid; and contend that, as we know nothing of the manurial action of the latter, the nitrogen it contains should not be taken into account in estimating the value of that manure, but that it should be assumed to have no action on plants until the reverse is proved. As less than half the nitrogen of a Peruvian guano exists in the state of ammonia, and as by far the larger part of its manurial value is due to its nitrogen, it is manifestly a matter of great importance to the farmer to know whether he is justified in ignoring all that which exists in any other form; and the question is one which cannot be restricted to ammonia and uric acid, but may be raised with regard to any other nitrogenous compound; so that, should this view turn out to be well-founded, it might be necessary to fix, by elaborate and frequently-repeated field experiments, the special agricultural value of nitrogen in every form in which it is used by the farmer—a course which would inevitably involve him in great difficulties and uncertainties.”
In the end, Anderson’s experiments established that Liebig was wrong. He wrote (p.485):
“They [his experiments] appear, then, to establish beyond all doubt that uric acid is capable of promoting the growth of plants, and that, as a source of nitrogen, it is on the whole equal to sulphate of ammonia or guano.”
It is now known that many of Liebig’s assertions regarding the application of artificial fertilizers were wrong. Indeed, for a while he reversed his position on the value of nitrogen fertilizers, believing that precipitation of ammonia from the atmosphere was enough to feed plants. What was right, however, was Liebig’s use and acceptance of experimentation as the correct way to advance science. He was also right about the overarching principle that artificial fertilizers could work, a fact proven by successors to Liebig’s work.