DR. AITKEN ON THE CHEMISTRY OF AGRICULTURE.

Oamaru Mail, Volume IV, Issue 1033, 12 August 1879, Page 2 (Supplement)

DR. AITKEN ON THE CHEMISTRY OF AGRICULTURE.

The last of tlie course of lectures on chemistry in its application to agriculture was delivered by Dr. Ait ken in the Hall of the Highland' Society in April last. The subject was "Artificial Manures." He referred to the former lecture, in which it was |shown that by the use of farmyard manure alone the character of the soil suffered a gradual change ; it became richer in organic matter and potash, and poorer in phosphoric acid and nitrogen. In the case of thin calcareous or sandy land, no application could be better than well-rotted farm-yard manure for improving the chemical and physical character of the soil. On rich, fat land the case was different. The amounts of organic matter and potash accumulated on the soil from the sole use of farm-yard manure -J ere out of proportion to the wants of the crop ; and it was found that in such cases the application of phosphatic and nitrogenous manures had the effect of greatly increasing th<} fertility of the soil. To conclude from this, as some had done, that farm-yard manure was a clumsy and inefficient kind of application compared with the more concentrated manures now so largely employed in agriculture, was to take a very subsided and erroneous view of the matter. Farm-yard manure was, and must ever continue to be, a most valuable form of manure, whose, excellence was not to be measured by its chemical composition alone, but by its physical and physiological character as well. It was the form of manure which required the farmers' greatest attention in every way, whether in the skill displayed ill the making of it, the care bestowed in the preserving of it, or in tire eoonomy and judgment displayed in its -application. There was no direction in which the farmer could uxore certainly save hundreds

of pounds than in the judicious management of farm-yard manure. The lecturer then proceeded to describe the various artificial manures which came to the aid of farm-yard manure in maintaining the fertility of the soil. They were mamly of three kinds—the various forms of phosphatic manures ; and the various forms of nitrogenous manures, which were important as supplying to the soil those ingredients that were most largely abstracted from it in the form of crops stock, and other exports of the farm ; and to these might bo added sulphuric acid, a substance which entered largely into the composition of crops, and in which mauy soils wero remarkably deficient. Lastly there wore other forms of manure which while they did not themselves enrich the soil much in the elements of plant food had nevertheless the effect of improving the condition of the land, and of rendering them readily available for the use of plants. This was a large and important subject, and one regarding which he believed farmers stood much in need of instruction. To treat it adequately would require not one, but a course of lectures ; and the large measure of success which had attended these lectures encouraged liim to think that a future course on the subject of manures would be acceptable to many members of the society. He then rapidly reviewed the various phosphatic manures,, explaining, by means of diagrams, thoir normal composition, and describing the various adult-orations, accidental or otherwise, which were sometimes met with in bono manures, superphosphates, and guanos. Ho showed liow tho various modes employed by chemists of stating the results of their analysis of. such manures, rendered it difficult for farmors unacquainted with chemistry correctly to interpret them. Ho thought that with a little unanimity on the part of chemists that difficulty might be removed.