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Limestone and Chalk Lime

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LIME, LIMESTONE AND CHALK These substances act in two ways : they supply calcium as a base, and they improve the physical condition of the soil. The need for calcium arises from the circumstance that fertile soils are rich in exchangeable calcium (see SoiL) ; if this becomes dis placed by hydrogen, a common occurrence in natural and farm conditions, a sour or acid soil is found unfavourable to vegetation. These sour soils are widely distributed in nature and they are dealt with either by using them only for crops tolerant of acidity, or by treatment with lime or limestone to supply the necessary calcium.

Lime and limestone are very effective on heavy arable soils, and they are often needed on lighter arable soils also : the need is indicated by partial failure of clover and by the prevalence of "finger and toe" (Plasrnordiophora) on the swede turnip or other crop of the Brassica family. They are less certain in effect on grass land especially where basic slag is used : instances of suc cessful use of lime are found in the north of England.

There being no necessity for purity, farmers often use impure lime or limestone so long as it is sufficiently cheap. It should, however, always be bought on analysis : samples of lime may contain 8o-95% calcium oxide, limestone may be of 95% purity.

Waste lime from various factories is sometimes available. The differences in action between lime and limestone are essentially minor and the choice between them is determined mainly by con siderations of cost and transport. Both should be somewhat finely ground before being applied, and if possible both should be applied in winter or early spring. Lime is fatal to certain animal pests, slugs and others, and should be used if they are of importance. The rate of application should be adjusted to the need which can be approximately estimated by modern analytical methods.

(E. J. R.) BIBLIOGRAPHY.-Selected bibliographies to the vast periodical scienBibliography.-Selected bibliographies to the vast periodical scien- tific literature of the subject will be found in S. H. Collins, Plant Products and Chemical Fertilizers (2nd ed., 1926) and Sir E. J. Rus sell, Soil Conditions and Plant Growth (5th ed., 1927). Reports of the Rothamsted and Woburn experimental stations may be read in Sir A. D. Hall, The Book of the Rothamsted Experiments (2nd ed., 1919) and the Journal of the Royal Agricultural Society, respectively. Among general works or special monographs the following may be consulted: H. Ingle, A Manual of Agricultural Chemistry (4th ed. 192o) ; G. S. Robertson, Basic Slags and Rock Phosphates (1922) ; Sir E. J. Russell, Manuring for Higher Crop Production (2nd ed., 1917) ; A Student's Book on Soils and Manures (2nd ed., 1919) ; Farm Soil and its Improvement (1923) ; and T. B. Wood, The Chemistry of Crop Production (2nd ed., 1924).

United States.

In the United States, practice in the pro duction and application of fertilizers differs somewhat from that of Great Britain and the Continent. Mixed or "complete" fer tilizer is usually used. This contains, as a rule, all three of the essential fertilizer elements—nitrogen, phosphorus and potassium —in some definite ratio. All the fertilizer materials may be applied simultaneously in. this way with a resulting saving of time and labour.

In making mixed fertilizers in America most of the materials which are described in the article above are utilized. Usually, superphosphate (acid phosphate) is manufactured at the factory and the other raw materials assembled. These are mixed with the superphosphate. In the United States superphosphate (acid phos phate) is graded according to the amount of available phosphoric acid (P205) it contains, which includes not only soluble in water but also that which is soluble, under certain very definite conditions, in a neutral solution of ammonium citrate of 1.09 specific gravity. Ordinarily, from 75 to 85% of the available phosphoric acid is water soluble. The grades produced range from 16 to 2o% available phosphoric acid. There is, also, a growing use for so-called double or treble superphosphate, which contains from 4o to 50% available phosphoric acid. This is prepared by acidulating phosphate rock with liquid phosphoric acid instead of with sulphuric acid.

The various ingredients of a mixed fertilizer must be chemically compatible, otherwise both the chemical and physical condition of the finished product would be seriously impaired. If improper mixtures are made, loss of nitrogen and reversion of available phosphoric acid to an insoluble form may occur and the product may become hard and lumpy instead of remaining fine and granu lar. The physical condition of the mixture is of much importance as it affects the ease and uniformity of distribution on the farm. Often mixtures are allowed to stand in storage for some weeks before bagging and shipping to permit the completion of chemical reactions among ingredients. The "cured" fertilizer is then milled to break up lumps before being bagged and shipped. Nitrogenous organic materials such as slaughter-house tankage, dried blood, cotton-seed meal, etc., have a decidedly beneficial effect on phys ical condition. These materials, however, are comparatively ex pensive as nitrogen carriers, and, in general, only the off-grade products, unfit for use in animal feeding-stuffs, find their way into fertilizers. Tankage from garbage, sewage and industrial wastes are also used. The present day trend, however, is distinctly away from extensive use of organic materials in mixed fertilizers.

The greatest quantity of fertilizer is used in the south-eastern States under cotton. Tobacco, too, is treated heavily, and potatoes in certain sections, as in Maine, require liberal amounts. In some sections of the east and south, it is used extensively with truck and cereal crops, but in the great cereal raising States of the middle west very little fertilizer is, as yet, consumed. In the fruit-growing districts of California and Florida fertilizer is re quired. In 1928 between 7 and 8 million tons of fertilizer were used annually in the United States. Owing to diverse requirements of widely separated localities a system has developed in the United States whereby comparatively small fertilizer works are situated in consuming districts catering to the special needs of each neigh bourhood. Some of these works manufacture their own sulphuric acid, superphosphate (acid phosphate) and mixed fertilizers; others buy acid and make superphosphate (acid phosphate) and mixed fertilizers; while still others are merely mixing units, buy ing all the fertilizer ingredients. Formulae used for mixed fer tilizers vary widely, depending on kind of crops, types of soil and local prejudices, so that many brands are on the market. Until recently the more popular formulae were of comparatively low analysis such as: 1.65% nitrogen (N2), equivalent to 2% ammonia io% phosphoric acid (P205), 2% potash (K20) and N2 (3% NH3), 9% P205, 3% K20. The present trend, however, is toward higher grade goods, such as : 4.12% N2 (5% NH3), P205, 5% and 3.3% N2 (4% NH3), 4% K20. Experiments are being made throughout the world on the direct application to the soil of concentrated materials such as urea, ammonium phosphate and mixtures containing between so and 7o% of nitrogen, phosphoric acid and potash. It is possible that in the future such mixtures will replace to a great extent the "complete" fertilizer combinations in use to-day.

The Journal of the Association of Official Agricultural Chemists contains many important contributions to the literature of fer tilizer chemistry. See also the division of fertilizer chemistry of the American Chemical Society; A. F. Gustafson, Handbook of Fertilizers, 1928; Collins and Redington, Plant Products, 1926.

(H. H. ME.)

acid, fertilizer, mixed, fertilizers, phosphoric, materials and ed