Potassium Dynamics in Calcareous Vertisols of Southern Iran
2011
Ghiri, Mahdi Najafi | Abtahi, Ali
The study was conducted to evaluate different forms of K, and release and fixation characteristics of 12 representative calcareous Vertisols of southern Iran. Mineralogical analysis indicated that smectite was the main clay mineral in the Vertisols, but some Vertisols had chlorite, illite, and palygorskite, as well as smectite in the clay fraction. Soluble, exchangeable, HNO₃-extractable, and total K ranged from 0.4 to 11.7 mg kg⁻¹, 127.1 to 435.6 mg kg⁻¹, 839.7 to 1942.4 mg kg⁻¹, and 4971.5 to 11427.3 mg kg⁻¹, respectively. Cumulative K released to 0.01 M CaCl₂ during 1496 h ranged from 167.7 to 244.9 mg kg⁻¹ for surface soils and from 109.1 to 198.0 mg kg⁻¹ for subsurface soils. Generally, the studied soils fixed 14–38% of the added K. The K fixation in different soils correlated significantly (r = 0.90, n = 42, p < 0.01) with the smectite content in the clay fraction and cumulative K released correlated significantly with illite content in the clay fractions (r = 0.79, n = 42, p < 0.01). Results indicated that clay mineralogy of Vertisols is a key factor affecting dynamics of K in the soils and thereby sustainable management of K in crop production. Generally, we concluded that calcareous Vertisols in southern Iran have sufficient K for plant uptake, but with intensive crop production and without application of K fertilizers, these soils will be transformed to K depleted soils in the future. Thus, application of K fertilizers in long term management of plant production may be required.
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