Cation Behaviour in Calcareous and Gypsiferous Soils Amended with Compost and Biochar

• Zahraa M. Abid Al-Taie1, Qahtan D. Essa Al-Khafagi2

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The aim of the study was to investigate the role of organic amendments (compost and biochar) in the sustainability of agricultural soils of two soil types. The study was conducted on two different soils (calcareous and gypsum), with compost and biochar added at four levels (0% and 2% compost, 2% biochar, and 1% compost + 1% biochar) by soil weight, the soil was packed into plastic columns (25 cm long and 7 cm in diameter). The experiment was conducted by adding irrigation water (river water) to each column in a volume equivalent to the pore volume, and alternating wetting was carried out for ten cycles, with a seven-day interval between each cycle. The soluble cations (Ca⁺², Mg⁺², Na⁺ and K⁺) were measured in the soil samples after the first, fifth and tenth cycles. The results indicated that there was a clear variation in the concentrations of these ions in the study soils when different irrigation intervals and different application rates of organic amendments were used. With regard to the levels of organic amendments added to the study soils, these played a clear role in increasing soluble Ca⁺² values; the results showed that the treatment combining compost and biochar was superior in reducing soluble calcium values, achieving a statistically significant reduction of 10.76% compared to the control treatment. As for soluble Mg⁺², the results showed that the treatment involving the mixture of compost and biochar led to an increase in its concentration, outperforming the other treatments and achieving a statistically significant increase of 17.83%. When comparing the two study soils, the variation in gypsum soil was generally higher than that in calcareous soil; As for the irrigation intervals, there was a gradual increase in the values of soluble magnesium and potassium with an increase in the number of irrigation intervals, starting from (C₁) after 7 days up to (C₁₀) after 70 days, conversely, there was a gradual decrease in the levels of dissolved calcium and sodium as the number of irrigation cycles increased, starting from (C₁) after 7 days up to (C₁₀) after 70 days.

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