Comparison of and correlation between the characteristics of agricultural topsoil and subsoil at the southern coast of Finland

Topsoil and subsoil samples were taken at 382 sites from the agricultural area of Viikki Experimental Farm, University of Helsinki. The samples were determinated for particle size distribution, pH(CaCl2), organic C %, at pH 7 exchangeable Ca, Mg and K, effective cation exchange capacity (ECEC), exchange acidity (AI + H) and plant available (Bray 1) P. The differences between topsoil and subsoil were studied taking into consideration the fertilization and liming during the past ten years before sampling. The correlations between soil characteristics were also studied. The clay (< 2 µm) and silt (2—20 µm) contents, exchangeable Mg and exchange acidity were lower in the topsoil than in the subsoil; as for the remaining characteristics, the values for topsoil were higher than those for subsoil. The subsoil seemed to be more heterogenic than the topsoil. There was a closer correlation between exchangeable Ca, Mg and K and the clay content in the subsoil than in the topsoil. In Litorina soils, there was a weak correlation between exchangeable cations and clay. It is more difficult to predict the cation contents on the basis of soil particle size distribution in soils cropped intensively, since fertilization and liming have changed the original contents. Vertical movement of applied Ca occurred slightly, possibly because the topsoils were rich in organic C. There was some correlation between organic C and exchangeable Mg or K, indicating a minor effect of organic matter on the leaching of these cations. The plant available P content of the subsoil was about 10 % of that of the topsoil irrespective of the amount of P applied. Clay and organic C contents were the main constituents of effective cation exchange capacity in the topsoil; in the subsoil the significance of clay was greatest.