Effect of Low Temperature Heating of Potassium-Depleted Soils on Secondary Potassium Release to Calcium Chloride and Wood Vinegar and Fixation

Abstract

Potassium behavior in calcareous soils are very complex and are affected by several factors, such as the content of carbonates and soil heating. In the present research, the comparison of four calcareous soils with varying amounts of carbonates, different mineralogy, and texture (collected from Fars province, southern Iran) was compared to analyze the content of K species, K release by solutions of 0.01 M CaCl₂ and 1% wood vinegar, and K re-fixation. The study also investigated the impact of heating K-depleted soils to 100°C on the secondary release and re-fixation of K. The results showed that the studied soils contained 3–60% carbonates, 14–53% clay, and a relatively similar mineral composition: smectite, illite, chlorite, palygorskite (in dry areas), and vermiculite (in humid areas). Wood vinegar extracted more K from soils with less carbonates than CaCl₂, while this difference was not significant for Fluvisols, which contains about 60% carbonates. Mollic Vertisols with low carbonate content (about 3%) and high levels of clay and smectite released less K in the initial phase. However, K release by this soil decreased less in the second phase, indicating the higher buffering capacity of Mollic Vertisols in providing soluble K. Heating the soil increased the secondary release of K, but decreased the amount of K re-fixation in soils treated with CaCl₂. Generally, Mollic Vertisols fixed more K than other soils. In addition, the type of extractant had no effect on the content of K fixation in the studied soils except Mollic Vertisols. However, wood vinegar reduced the K fixation content in Mollic Vertisols compared to CaCl₂. In general, it can be concluded that wood vinegar can provide more K to the plants without dissolving K-bearing minerals compared to CaCl₂. In addition, soil heating can influence the process of K release and fixation in K-depleted soils.