Transformations of different soils under natural and anthropogenized land management

Abstract

The aim of the study is to determine changes in the morphological, physical and chemical properties of soils of Lithuanian agroecosystems caused by their anthropogenic transformation. Summarized data on 33 soil profiles, 5 relatively natural mature forest soils and 28 anthropogenically affected soils, investigated in 2015–2018, are presented. The structure of the soil profile and its variation, the thickness of Ah(p) horizon, the soil bulk density and total porosity, the soil organic carbon content and its qualitative characteristics in A horizon were examined. The study showed that Retisol (RT) and Planosol (PL) are mostly degraded ex-situ due to the agrogenical effect: disruption of the genetic profile and the removal of the soil organic carbon (SOC) are ongoing, therefore bulk density increases and total porosity decreases. Luvisol (LV), Cambisol (CM) and Gleysol (GL) are most affected by in-situ erosion: soil is compacted and total porosity is decreasing. The loss of SOC due to the removal of biomass contributes to the increase in soil density. The Retisol profile horizons in the upper part are changed from O-Ah-E-E/B to Ap-E/B. The natural Luvisol profile, described as O-Ah-E-Btg-BCkg, is changed into the sequence of Ap-Ahm-BCk. In archaeological areas, the initial topsoil O-A horizon transformed to a complex cultural layer consisting of terric Ah and buried Ah horizons. When anthropogenic soil Ah soil horizons become deeper (from 10–15 up to 25–30 cm thick) due to deep ploughing, the E horizon is disturbed and partially mixed and incorporated into Ap horizon. The properties of Ap horizon differ from those of Ah and AhE horizons, from which it has developed. The bulk density increases from 0.8–1.08 to 1.55–1.75 Mg m -3 , while the SOC content decreases from 30–40 to 11–14 g kg -1 in Ap horizon. Humification degree in the soils of mature forest is amounts to about 25.5%, while in agrogenized soils it varies greatly and amounts about 14%. The most favourable conditions for soil organic matter (SOM) humification and SOC sequestration are in perennial grassland, when biomass is not removed, as well as in mature mixed forests. The ratio of carbon of mobile humic and fulvic acids (C MHA :C MFA ) varies from 1.02 to 1.54 in relatively natural soils of mature forest, in arable soils varies within the range of 0.58–1.02, and in meadows – 0.91–2.82, indicating declining SOC sequestration. In order to solve soil problems related to soil agrogenization, the aspects of SOC content and intensity of land use should be considered. Usage of Luvisol and Cambisol for agriculture, crop rotations must be observed and organic fertilizers must be used in combination with mineral fertilizers. From soil conservation viewpoint, arable farming in Retisol and Planosol should be replaced by grassland and livestock farming.