The Humid Soil: Process and Time

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pEDOLOGY is a young science. It began with description, and it has centered on the mid-latitudes. Soils were first described and classified morphologically; the study of process came later. Pedologists became well acquainted with mid-latitude soils and had a fair understanding of the processes that produced them, but of tropical soils they had only a dim idea. They understood these soils to be very different from the soils familiar to them, and they assumed that the difference must be due to a fundamentally different process at work in the tropics. This common assumption that the soil-forming processes are fundamentally different in the tropics and in the middle and higher latitudes is epitomized by the names for high latitudes and laterization for low latitudes. Podzolization is understood to be a process by which soils are first leached of their easily soluble components and then the iron and manganese family are preferentially mobilized from the upper horizon, with some accumulation of iron in the lower horizon. Laterization is thought of as the opposite process. The silica is preferentially mobilized, and the iron and aluminum accumulate in the surface horizon as a residual concentration.' In this discussion we shall consider several papers, especially those concerned with process and time, that have recently appeared in the British Journal of Soil Science. Our purpose is to show that from the equator to high latitudes under humid conditions there is only one fundamental soil-forming process. Since there is more agreement on the podsolization process and since papers are available that have considered the degree of development with time, we shall begin by discussing papers on podzolization in Great Britain.