OXIDATION-REDUCTION PROCESSES IN THE SOILS OF RICE AGROCENOSES OF THE KUBAN REGION (RUSSIA)

Abstract

Background: The studies were carried out on the Maryano-Cheburgolsky irrigation array in the Krasnoarmeisky district of the Krasnodar Territory. Aim: This work aims to study the oxidation-reduction processes and activity of iron compounds in meadow-chernozem and meadow-boggy soils of rice agrocenoses of the Kuban region. Methods: Soil samples were taken from paddy fields occupied by rice and perennial grasses, in which the pH value, redox potential (Eh, mV), magnetic susceptibility (χ×10-3 S.I. units), and the content of active iron compounds (FeO and Fe2O3, mg/100 g) were determined. Results and Discussion: The reductive processes created in the soils of rice fields after flooding led to the transformation of poorly soluble Fe2O3 compounds into more active reaction forms of FeO. The maximum content of FeO and the minimum amount of Fe2O3 were recorded during the period of negative Eh values. The maximum reduction of iron in meadow-boggy and meadow-chernozem soils was achieved by the phase of flowering of rice plants at Eh = -127, pH = 7.36 units, rH2 = 10 and Eh = -152...-167 mV, pH = 6.89-7.10 units, rH2 = 9, respectively. Conclusions: In the soil of permanent rice cultivation, the dynamics of Eh and iron compounds are similar to the fields of rice crop rotation. In non-flooded soils of rice fields under perennial grasses, the oxidative regime prevails, and the transformation of iron compounds is not expressed. The minimum values of χ coincide with the maximum content of ferrous iron in soils at negative Eh values, which corresponds to the rice flowering phase. Correlation coefficients of χ with Eh, FeO, and Fe2O3 equal from +0.66 to +0.75, from -0.69 to -0.84, and from +0.74 to +0.77, respectively. The χ value increases in the soil under crops of perennial grasses with a predominance of oxidative processes. The correlation coefficient between χ and Fe2O3 equals from +0.83 to +0.90.