Vol 73, No 4 (2018)

Color change during the drying of samples of medium-loamy slightly ferruginous gley taken from a pit of alluvial swampy mucky-gley soil in the Moscow region was studied using a portable spectrophotometer in the field and at a laboratory. Despite the absence of visual differences, instrumental examination revealed particular changes in the lightness and yellowness of soil samples. Two types of dependencies were determined: at short-term field study and at long-term gley drying at the laboratory. The latter dependence of lightness or yellowness on the duration of the drying period is logistic: there are two steady states of the parameters and a transition area between them, where their values sharply increase. The slow yellowing of the studied gley puts the presence of green rust mineral into question, which is typical for higher ferruginous gley soils. Drying exerts different effects on the rate of color change in the top and deep parts of the visually uniform gley horizon. This is clearly related to its chemical (and mineralogical) differentiation.

Potassium fixation capacity has been estimated in chernozem samples taken from the variants of a field experiment with a single application of potassium fertilizers (0, 70, 140 and 280 kg/ha) after a six-year break in fertilizer use. The potassium fixation capacity of chernozems inferred from the change of exchangeable potassium content after the incubation of the samples with a fixed dose of a potassium fertilizer (50 mg/100 g) ranged from 45 to 47 mg/100 g, or 91–95% of the potassium introduced in the different experimental variants. The actual potassium fixation capacity may be considerably higher than the values measured. Potassium fixation capacity inferred from the change of non-exchangeable potassium content after incubation of the samples with a fixed dose of a potassium fertilizer ranged from 32 to 38 mg/100 g, or 64–75% of the potassium introduced, in the experiment variants. Elevated mobility of fixed potassium in the case of a stronger treatment (2 M HCl, the Pchelkin procedure) and the associated decrease in the difference between the mobile potassium levels before and after incubation with a specific dose of the element may be used to explain this discrepancy. No reliable differences with regard to the average values of potassium fixation capacity were detected between the experiment variants, but the maximal values were observed in the control variant and decreased gradually as the fertilizer doses increased.

Concentrations of heavy metals (HM) that may have a significant negative impact on plants and soil microbiota have been identified at different pollution levels for sod-podzolic, gray forest, leached chernozem and chestnut soils. The investigated soils can be arranged in descending resistance to HM in the following order: leached chernozem, gray forest soil, chestnut, sod-podzolic soil. A comparison of the results of phytotoxicity determination in growing plants on soils and on soil extracts showed that phytotoxicity on soils polluted with HM appears at lower concentrations than on soil extracts. This is a consequence of low solubility of heavy metal compounds that are strongly sorbed by the mineral and organic components of soils, and also remain in the form of poorly soluble compounds.