Influence of the Moisture Content of Soddy-Podzolic Soil on the Contents of Mobile Forms of Iron, Manganese, Nickel, Copper, Cobalt, and Zinc

Excessive moistening of soils can lead to changes in a number of soil properties, which in turn affects the content of mobile forms of elements. However, the gradations of soil supply with trace elements have been developed for air-dry samples of automorphic soils and, therefore, may not adequately reflect the real picture for soils under conditions of overmoistening. The aim of this work is to assess changes in the content of mobile (available) forms of trace elements in soil samples of field experiments with different rates of mineral fertilizer application on soddy-podzolic sandy soils (Stagnic Podzols (Pantoarenic, Buthyloamic, Abruptic, Aric)) under different moisture conditions. We determined the contents of mobile forms of Fe, Mn, Ni, Cu, Co, and Zn in the soil samples from the plow layer (0–20 cm) and the subplow layer (20–40 cm) taken on the experimental plots without mineral fertilizers (control) and with moderate and high rates of fertilization. Mobile forms of elements were extracted from the air-dry soil samples, samples with field moisture, and samples incubated in laboratory at different moisture contents (60 and 100% of the field capacity) for three and six weeks. It is shown that different moisture content in samples can significantly change the amount of mobile forms of Mn and Fe, which in turn affects the mobility of other elements—Cu, Co, and Ni. The content of mobile forms of most of the studied elements, except for Zn, is higher in moistened samples than in air-dry samples. An increase in the content of mobile forms of Cu and Co under conditions of moistening in the incubation experiment changes the gradation of soil supply with these trace elements from low to high, which attests to the need to adjust the existing gradations with due account for the soil moisture content.