CHAPTER XXV.
ON THE VALUATION AND ANALYSIS OF MANURES.
Value of Chemical Analysis.
The value of a manure to the farmer depends on the proportion of nitrogen, phosphoric acid, and potash it contains, as well as—and this is hardly less important—the condition in which the ingredients are present. Since these facts can alone be determined by a chemical analysis, it is obvious that manures should always be purchased with a chemical analysis. It is unfortunate, however, that very often a chemical analysis, even when procured, is unintelligible. It may be of advantage, therefore, to say a word or two on the correct interpretation of the significance of the data furnished in the ordinary chemical analysis of manures.
Interpretation of Chemical Analysis.
The first thing that the farmer ought to look for in the analysis of a manure is the amount of nitrogen, phosphoric acid, and potash which the manure contains.
Nitrogen.
The percentage of nitrogen in a manure is generally stated as equal to its equivalent percentage of ammonia. Very often, indeed, in the older analyses, its equivalent of ammonia was alone stated. Now this statement does not necessarily imply that the nitrogen in a manure is actually present in the form of ammonia. Thus, for example, when it is stated in an analysis of bone-meal that it contains 3.5 per cent of nitrogen, equal to 4.20 per cent of ammonia, it is not to be inferred that bone-meal actually contains nitrogen in the form of ammonia. In point of fact the nitrogen is present in an insoluble, slowly available, organic form, which possesses a manurial value very inferior to that possessed by ammonia. This custom is a most unfortunate one, and is much to be regretted, as it is often liable to give rise to serious misunderstanding. It must be remembered, therefore, that an ordinary chemical analysis does not always specify the exact form in which nitrogen is actually present. It is nevertheless of importance for the farmer to know this, of which the nature of the manure analysed is generally a good indication. Unfortunately this is not shown in the case of mixed manures; and this constitutes one of the reasons why mixed manures are sometimes to be regarded with suspicion.