Neoformations (Nodules and Placic Layers) in Surface-Gleyed Loamy Sandy Soils of the Northern Part of the Tambov Plain

Abstract

In the middle part of the profiles of light gray soils (non-gleyed, deeply gleyed, weakly and strongly gleyed) on silty loamy sandy two-layered deposits of the river terraces in the Tambov Plain, placic layers are formed. Nodules are confined to the arable layer, if surface water stagnation occurs. Angular black nodules of less than 2 mm in size with a high Mn content are specific for weakly gleyed soils, grayish brown nodules of 7–10 mm in size are common in strongly gleyed soils. The Cd and Pb accumulation coefficients in the nodules reach 100–300, those for Co and Mo are 10–100; for Zn and Cu, 2–5; the content of P₂O₅ is 1.0–1.5%, the content of organic matter in the nodules is 1.8–2.5%, and it has a fulvic nature (C_ha/C_fa < 0.4). The placic layer density reaches 1.6 g/cm³, and the aeration porosity is reduced to 3–6%. They are highly acidic, 1.5 to 3 times higher in the contents of clay, Al, Fe, Mn, and trace elements than the enclosing material. A reliable quantitative criterion for the evaluation of the agroecological status of light gray surface-gley soils can be the Fe/Mn ratio in 1 N sulfuric acid extract from the nodules (bogging factor according to Zaidelman and Ogleznev).