The problem of cambisols identification in Lithuania: landscape evolution approach

Abstract

Cambisols are considered to be the most productive soils in Lithuania however the identification of these soils is still one of the most controversial issues in terms of their diagnosis and classification. This is because the improper accommodation of certain soil into above mentioned group very often hides the problems caused by the intensive use of soil in clayey lowlands – erosion and loss of SOC. Although the Cambisols are classified according to the Lithuanian soil classification (LTDK-99) harmonized with FAO and WRB, however, their identification is debatable in connection with the Lithuanian Genetic Classification of Soils (TDV-96), the development of the Lithuanian landscape and the geological and geomorphological processes that formed the territory of Lithuania. The authors of the presentation put forward hypothesis that the natural conditions of Lithuania in clayey plains lead to the formation of Luvisols, whereas the Cambisols there are identified without the properly assessing of deep ploughing and erosion effects that occurred during the agrogenization of the landscape. Consequently, these factors should be directly related with the changes that occur in the morphology of the tested soil profiles. As from the point of view morphological appearance, an illuvial Bt and cambic Bw horizons looks very similarly however they are formed under the influence of fundamentally different soil formation processes. In natural conditions (i.e., without any major human intervention), soil horizonation sequence consists of the following combinations: O-A(h)-E-Bt-B(α)-… for Luvisols, and O-A(h)-BwB(α)-… for the Cambisols. However, in the agrogenic conditions, i.e., after deep ploughing and erosion, the O-Ah-E topsoil part of Luvisol becomes destroyed and turns into A(h). Consequently, the B horizon with clay accumulation can be interpreted both as a Bw and/or a Bt horizon, since there are missed the objective topsoil features to show their nature and allow us to distinguish them from each other. Therefore, in order to solve this diagnostic problem of Cambisols, we should be guided not only by the morphology of certain soil profile and/or the distribution of clay particles, but also supported by the mineralogical studies of secondary clay minerals. This approach would be very relevant in order to identify the beidelite and nontronite – minerals of the montmorillonite group – formed during the clay particles formation in situ. The development of the landscape (features of agrogenization, modeling of the primary surface) and changes in the soil cover due to possible erosion should also be assessed.