THE VERTICAL DISTRIBUTION OF SOIL BASES AND ACIDITY IN SOME ILLINOIS SOILS

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Abstract
Soils from treated and untreated plots on 8 Illinois experiment fields representing as many soil types were sampled by 3- to 4-inch strata. These soils were subjected to the following tests and analyses: pH, Comber KCNS test, buffer action, Hutchinson-MacLennan and Hopkins lime-requirement tests, total and exchangeable Ca and Mg. Several different solutions for the replacement of Ca and Mg were tried, with the final adoption of ammonium acetate. In all cases the pH values increased with depth, the increase being greatest in the Joliet soil whose subsoil is highly calcareous, and least in the soils from the Mt. Morris and Oquawka fields. The Comber test agrees closely with the pH values. The Hutchinson-MacLennan lime requirement data compare favorably with electrometric titration with Ca(OH)2 to a pH of approximately 7.0. Only in the southern soils does the lime-requirement as measured by the Hutchinson-Mac-Lennan test increase with depth. These soils are characterized by a comparatively high total acidity, of which a very large proportion is the so-called exchangeable acidity, and only a small part is hydrolytic acidity. In a very general way the pH values vary with the total Ca content, with the exception of the Black Clay Loam at Hartsburg. In most instances the total Mg content in the surface horizon is approximately equal in amount to the Ca content in that horizon, but in the subsoils there has been a greater accumulation of Mg than of Ca. The curves for exchangeable Ca and Mg follow the curves for total Ca and Mg respectively, but the percentage of change with depth is greater with the exchangeable fraction than with the total amounts of these bases. The application of limestone increased the pH and reduced the lime-requirement, and increased the total and exchangeable Ca content of the surface layer in every case. The influence of limestone penetrated to different depths in the various soils, but only in one soil, Oquawka, was it observed below the A horizon. This influence could be detected more readily by the pH determination than by any of the other tests. Natural soil variations were greater than any measurable influence of treatments other than liming. The coefficient of correlation of crop yields with total and exchangeable Ca and with acidity of the A1 horizon is very high in the southern soils, but low in the soils from the northern fields. The pH of the A1 horizon of the southern fields and 3 of the 5 northern fields was approximately identical although crop yields were considerably greater in the northern fields. The data indicate that the pH may not be a primary factor in crop production so far as its direct effect on crop growth is concerned.

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