THE ESTlilATlON OF SOIL ACIDITY A N D T H E LIME REQUlREilENTS OF SOILS. BY F. P. V E I T C H . lie;ei.:cd A!.au,t
i j . 1912.
the past few years, it has been definitely shon-n that the reaction of a soil eserts a marked influenceon its crop-producing pokver. \\-bile the reaction afr'ects the chemical and the physical condition of the soil to a considerable extent, the growth of plants is more directly affected by the action of the acids on the plant roots. and upon the micro-organisms of the soil. The importance of the inatter has led to the elaboration of several methods for determining the aniotiiit of acids in soil, but, on.ing to the esceedingly small amount usually present in ordinary arable soils, the influence of other material, and the constant changes taking place in the soil. iione of these methods has shown a close relation between crop pro(1uction a i d the amount of acidit)as tleterminetl by an!. of the methotls. \\-heeler, Hartivell. and Sargentl have recently niade a critical esamination of the methods ivliich ha]-e been proposed for this pLirpose, checking the chemical nietliotls by field esperiments. T h e investigators were iinable to correlate the chemical results obtained l i ~ . any of the methocls esainined Tvitli the fieltl results. iiut regarded as promising the titration of tlilute ammonia ivhich had been in contact with the soil for some time. and also a method based on the evolution and estimation of the carlion clioside freed from calcium carbonate by the acid soil on boiling them together i n i n t e r . Tt has not seemed advisable to the ivriter to give more study to either of these methods. liecause any solution placet1 in contact \ ~ i t l ia soil. no matter \vliether acid or alkaline. ]vi11 be decreased in strength through adsorption or physical reaction between the solution ant1 t h e soil : and \\-e 1iaT.e no certain means of measuring the amount thus aclsorbetl. Further. cnving to the deflocculatiiig po\ver of amnionia. it is practical1)- impossible to get even an a 1) p r o s i ma t el!. c 1ea r filtrate or stipe r n a t a n t 1iqui tl an t 1 t li c a iiiou n t of acid as tlcterniinecl is more or less afiected hy this fact. \\-it11 regard t o thc evolution and estilnation of car11011 dioxide, the \
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ESTIMATION O F SOIL A C I D I T Y .
I121
evolution continues indefinitely, and whether it is due to reaction betiveen the soil and the carbonate o r to the oxidation of the organic matter of the soil is not definitely known, though it is probable that it is more largely due to the first-mentioned reaction. After a great deal of experimenting the writer has devised a method in which lime-water is used to neutralize the acid material in the soil. T h e method is based on the fact that the small excess of lime-water present, after the neutralization of the acid material, is converted into carbonates and bicarbonates, the boiling solution of which gives an alkaline reaction with phenolphthalein. S o effort has been made to secure great refinement or close duplication of results, because the problem is a practical one in which the application of several hundred pounds of lime, more o r less, per acre has but little economic or agricultural significance. I t may be said, however, that the writer has reason to believe that the method will give duplicate results accurate to one hundred pounds of lime per acre foot of ~.jOO,oOO pounds. The method is as follows : For the preliminary test, to three portions of IO grams each of the soil in platinum dishes add jO to 60 cc. of distilled water, and different amounts of standard lime-mater. F o r example, to the first IO cc., to the second 20 cc., and to the third 30 cc.of lime-water are added. Dry down at once on the steam-bath, transfer to a stoppered Jena flask with IOO cc. of distilled water, allow to stand over night, with occasional shaking, filter (the filtrate should be clear o r but faintly turbid), take 50 cc. in a Jena beaker, add a few drops of phenolphthalein solu'tion, and boil until the appearance of the pink color, o r in the case where no color is developed to a volume of about 5 cc. Then with the two portions of treated soil, one of which has been rendered alkaline by the added lime-water and the other of which is still acid, as guides, prepare three fresh portions of IO grams each, and add lime-water as before, except that the amount added to a dish differs from that added to another, by only one o r two cc. Dry, allow to stand, filter, and treat exactly as before ; the smallest amount of lime-water which gives the characteristic pink with phenolphthalein is taken as the acidity equivalent of the soil. From the data thus obtained, the acidity and lime requirements of the soil may be calculated.
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51' cc. filtrate I)oileil.
Acid w i t h cc. C a ( 0 H I?.
So. I Siiti~rriit,.I: I . . . . . . . . . . . . . . . . . . S o . 2 Jairiestowii, I
