SOME PRINCIPLES OF LIMING.

Otago Witness, Issue 3382, 8 January 1919, Page 8

SOME PRINCIPLES OF LIMING.

although we grant that there is a fund of truth in the old saying "lime and lime without manure makes both farm and farmer poorer," yet the agricultural use of lime on af great deal of our Dominion lands may be considered as an investment on which the farmer is justified in expecting a profitable return, and "hence the rate of application should be such that the highest return may be secured for the money available for investment. The soils of New Zealand are in a great measure acid, and require liming before they can be made to produce as they should. The most profitable form of lime for a farmer to use depends sometimes on how far it has to be carted or railed. That which is nearest to hand at a reasonable price should be thoroughly investigated. Many form's of lime are on the markets—burnt lime, crushed lime, pulverized limestone, etc., all useful for correcting soil acidity. It has been our experience that the best way to apply lime is on ploughed land that has been harrowed at least once, although it may be safely applied at any stage in the rotation, but as some crops have high lime requirements (clover, lucerne, etc.) it is only reasonable to make adequate provision in good time, say a year before the big demand is expected, so that the lime had had time to have been well mixed with the soil. s Of course, an application by way of top-dressing on the growing crop is not to be despised, but the results, naturally enough, are not so good as when it is thoroughly worked in the soil. In the latter connection we are of the opinion that commensurate benefit will only result when the lime is finely ground- or air-slaked, and it is only reasonable to expect better results on sandy soil than on clay, because it works, into the open, handy soils more quickly. It has been pointed out at various times in these columns that the value of lime (oxide of lime) represented by burnt lime, depends upon its purity, and that for immediate effect the value of carbonate of lime, represented by ground or pulverized limestone, depends upon its purity and the fineness of grinding. "It is plain, then,"' says a contributor to the Montreal Witness, "so far as immediate efficiency in the soil is concerned, that the value of the latter as compared to the former depends on the equivalent value of carbonate when calculated to oxide, and how nearly its fineness approaches the fineness of slaked lime." In other words, what is the equivalent lime oxide calculated from the lime carbonate, and how much fine material that 'nsy be considered immediately available is "there in the pulverized limestone? The relative value of lime carbonate to oxide of lime is in the ratio of 56 to 100; or, in other words, 100 pounds of carbonate will produce 56 pounds of oxide on burning. Stated in still another way, 100 pounds of carbonate must be used to produce the same chemical effect as 56 pounds of oxide. It is not possible within the limits of reasonable cost to grind limestone so that it is all as fine or even nearly as fine as* slaked lime, and this has 'led to proposed standards or specifications regarding this feature. In general terms, it may be stated that the finer limestone or similar material is' ground the more it will cost, and the finer it is ground, the more quickly soluble and effective it will he in the soil. Naturally, however, there is a point where added exposure for fine grinding is not warranted because the increased crop production does not offset the increased cost of material. Results from field tests regarding the- efficiency of limestone of different degrees of fineness, while naturally varying considerably as influenced by differences in soil, crop,, and climate, all agree in support of the contention that some degree of fineness is necessary for immediate effect. It may safely be assumed, therefore, that in the case of ground or pulverized limestone it is only the material of certain fineness that is immediately available that is comparable in value with fine material obtained on slaking burnt lime, and for immediate results fine material is all that should be considered in computing the relative value of such products. Coarse material, though not immediately available, naturally is of some value, is slowly dissolved, and has its effect on. the soil, but this naturally varies with varying conditions. Just what degree of fineness should be required in pulverized limestone may differ somewhat, but a specification that a large percentage shall pass a 60-mesh sieve probably comes very near the medium between very fine material at very high cost, and coarse material produced cheaply.