Soil buffering capacity
Soil buffering capacity — the ability of soil to resist changes in soil reaction. Buffering capacity is characterized by the cation absorption capacity (T), the composition of absorbed cations, and the cation-anion composition of the soil solution.
Importance
Soil buffering capacity is manifested in resistance to temporary changes in the concentration of the soil solution caused by a lack of moisture, uneven or periodic application of fertilizers and soil amendments. Soils with high buffering capacity, cation exchange capacity, and a diverse composition of absorbed ions easily retain maximum permissible single doses of soil amendments and fertilizers in an absorbed state without a significant increase in the concentration of the soil solution. In contrast, soils with low buffering capacity cannot retain large single doses of soil amendments and fertilizers without an increase in the concentration of the soil solution and losses of nutrients due to leaching; therefore, on such soils fertilizers are applied in split doses.
The importance of soil buffering capacity is used to calculate optimal doses, forms, timing, and methods of fertilizer application and soil amendments for agricultural crops.
Mechanism of action of soil buffering capacity
Soil buffering capacity is due to the presence in the soil solution of weak organic and mineral acids and their salts, which participate in the reactions:
In the presence of an acidifying factor in the soil, that is, when hydrogen ions appear in the soil solution, they exchange with the cations of the SAC, resulting in a neutral salt, and the reaction of the solution does not change:
The buffering properties of soil against acidity increase with increasing base saturation of soils and with a shift from neutral to alkaline soil reaction.
In the presence of an alkalizing factor, that is, when hydroxide ions appear in the soil solution, for example Ca(OH)2, the calcium cation displaces an equivalent amount of hydrogen ions from the SAC, resulting in water, and the reaction of the solution does not change:
Buffering properties against alkalization increase in neutral soils with increasing hydrolytic acidity, with decreasing degree of base saturation, and with a shift from neutral to acidic soils.
Properties
Under the action of acidifying and alkalizing factors, the reaction of the soil solution may change; however, the rate of change in soils with low cation exchange capacity is higher than in soils with high capacity. The higher the cation exchange capacity, the higher the soil buffering capacity.
Management
To increase soil buffering capacity, organic and mineral fertilizers are used in combination with periodic application of soil amendments.
References
- Yagodin B. A., Zhukov Yu. P., Kobzarenko V. I. Agrochemistry. / Ed. B. A. Yagodin. Moscow: Kolos. 2002.
- Mineev V. G., Sychev V. G., Gamzikov G. P. et al. Agrochemistry. Textbook. / Ed. V. G. Mineev. Moscow: Publishing House of the All-Russian Research Institute of Agrochemistry named after D. N. Pryanishnikov. 2017.
