Abstract
DURING and since the war the position in this country with regard to the supply of basic phosphatic fertilisers has undergone a radical change. On one hand, the ousting of the older Bessemer process by the modern open hearth process of steel-making has led to the virtual disappearance from the market of the high grade basic slag to which the agriculturist was accustomed, and its replacement by a totally different material of much lower phosphorus content and frequently of low “citric-solubility.” On the other hand, the development of the extensive deposits of rock phosphate in the Pacific Islands has rendered available greatly increased amounts of this material. The field experiments at Cockle Park, from which most of our knowledge of the value of basic slag in agriculture was derived, were carried out with the now obsolete high grade Bessemer material, and prior to Dr. Robertson's experiments practically nothing was known as to the fertilising value of the new open hearth slags; the experiments in this country on raw rock phosphate were also few in number and not very conclusive in result. Dr. Scott Robertson's experiments were carried out on several different farms in various parts of Essex during the years 1915-20, and were designed to test the relative fertilising value of Bessemer and open hearth basic slag, and of mineral phosphates, on permanent grassland cut for hay. The results of these experiments form one of the most important contributions which have been made in recent years to the literature of phosphatic manures, and their publication in book form is thus very welcome. It was found that on heavy soils of the London Clay and Boulder Clay the improvement effected by rock phosphates compared favourably with that due to high-soluble basic slags, especially in a wet season when the hay harvest was late, and on sour soils. The low-soluble fluorspar slags were definitely inferior, though still effecting a considerable improvement. At two of the centres where the experiments were carried out there was no response to phosphatic manuring, and the author produces evidence that this is due to the operation of another limiting factor, probably deficiency of potash. This point is of interest in connexion with the fact, well known to agriculturists, that basic slag is not invariably effective on all grassland. It is quite likely that some, at least, of these failures are due to a similar cause.
Basic Slags and Rock Phosphates.
By Dr. G. Scott Robertson (Cambridge Agricultural Monographs.) Pp. xvi + 120. (Cambridge: At the University Press, 1922.) 14s. net.
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P., H. Basic Slags and Rock Phosphates . Nature 110, 306–307 (1922). https://doi.org/10.1038/110306a0
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DOI: https://doi.org/10.1038/110306a0
