Agrogenic and Postagrogenic Changes in Physical Properties and Carbon Stocks in Dark-Humus Podbels

The changes in the physical properties and carbon stocks of dark-humus podbels (Luvic Albic Mollic Planosols (Epiloamic, Endoclayic, Aric)) during long-term agricultural use and postagrogenic evolution were studied. Soil samples were taken in three trials: control (without fertilizers), high rates of mineral fertilizers, and mineral fertilizers + manure + lime (Chaika Experimental Field Station of the Federal Research Center for Agrobiotechnology of the Far East, Primorsky region) and in the abandoned fields (15, 20, and 35 years ago). It was shown that the long-term application of mineral fertilizers increases the soil bulk density. Application of organic and mineral fertilizers and lime had a positive effect on the bulk density and structural characteristics of soils. The abandonment of agricultural fields and the cessation of mechanical tillage resulted in the restoration of the natural soil structure. The content of agronomically valuable aggregates increased, while their mean weighted diameter decreased in the upper horizon of studied fallow soils. The carbon content and stock in the upper soil layer decreased in the first years of the conversion of arable fields to unmanaged fallow. The carbon stock in the upper 50-cm layer increased with time.