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The influence of the redox regime on soil fertility and plant nutrition

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The influence of the redox regime on soil fertility and plant nutrition

The redox (redox) status of the soil directly influences its soil fertility and the availability of nutrients for plants. In the soil solution, mineral and organic redox systems constantly interact: O2–O2–, Fe3+–Fe2+, Mn4+–Mn3+–Mn2+, H2–2H+, SO42––H2S, CO2–CH4. An imbalance in these pairs can either block the uptake of key elements or lead to toxic poisoning of seedlings.

The water-air regime of the soil determines the pattern of organic matter transformation. Excessive moisture and a stable lack of oxygen slow down the decomposition of plant residues, which increases the proportion of fulvic acids and non-hydrolyzable residue in the humus. On the other hand, the periodic alternation of flooding and drying (on irrigated lands and in river floodplains) accelerates the decomposition of organic matter too much. This disrupts the carbon balance and leads to the dehumification of the soil.

Influence of redox potential (Eh) on plant nutrition

The availability of nutrients depends on the value of the redox potential (Eh), expressed in millivolts (mV). Both sharply oxidizing and deeply reducing conditions are dangerous for the normal development of crops. The boundaries for normal plant supply with iron, manganese, and nitrates are strictly limited by the Eh values and the pH of the soil.

  • Eh above 700–750 mV — deficiency of iron, manganese, and nitrogen
  • Eh 550–600 mV — optimal conditions for nitrification
  • Eh below 340 mV — onset of intensive denitrification
  • Eh 200–250 mV — accumulation of toxic forms of Fe and Mn
Eh range, mV State of the soil environment Impact on the plant nutrient regime
Above 700–750 Sharply oxidizing environment The mobility of iron, manganese, and nitrogen decreases. When high Eh and pH values are combined, manganese deficiency occurs.
550–600 Moderately oxidizing environment Nitrification proceeds most intensely, optimizing nitrogen nutrition.
Less than 340 Reducing environment The denitrification process is activated, leading to major losses of nitrogen from the soil.
200–250 Deeply reducing environment (anaerobic conditions) Ferrous compounds of iron and manganese accumulate in concentrations toxic to plants.

A decrease in the Eh potential to 200–250 mV under anaerobic conditions triggers the accumulation of compounds toxic to the root system: hydrogen sulfide (H2S), phosphatides, and ethylene.

To maintain the redox regime within optimal boundaries, an agronomist must manage the physical properties of the soil. Regulating the water-air balance and improving structure make it possible to prevent critical shifts in potential. A complex of standard reclamation and agrotechnical practices is used for this:

  • ploughing (improves aeration and increases Eh potential);
  • rolling (regulates density and moisture evaporation);
  • irrigation and drainage (allow for controlling moisture levels and preventing water stagnation).

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