The soil reaction profile
1929
Norton, E.A. | Bray, R.H.
Early in the process of soil formation, the pH of the A1 horizon of the soils in Illinois becomes 5.7, which seems to be a position of equilibrium between the accumulation of bases from the decay of organic matter and the loss of bases by leaching. This pH is maintained as long as the soil is able to support a good vegetative growth. It appears that a soil in this region which is productive must have been able to maintain surface pH of at least 5.7 in the virgin profile. The highest acidity which might be expected in the mature soils of this region under present environment is a pH of about 4.8. Differences in the rate of leaching were observed in immature soils. Soils developed on rolling well-drained topography were more acid throughout the profile than those developed on flat topography under poorly drained conditions. A significant difference was observed in the amount of leaching in two profiles of the same soil type differing only in the length of time they had been subjected to weathering. The pH of the Slick Spot profiles shows a good correlation with the texture, structure, and consistence characteristics as observed in the field and with replaceable sodium as determined in the laboratory. The above points lead to the conclusion that the reaction profile is a relatively stable soil character, and that it can be considered as an aid to the separation of soil types.
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