The effect of five-decade continuous horticultural practice on distribution of potassium forms in some soils in South of Urmia

Continuous horticultural practice may be manifesting some modifications on physico-chemical and different K forms of soil. To investigate this hypothesis, five soils subgroups (Typic Calcixerepts, Fluventic Haploxerepts, Typic Endoaquepts, Typic Halaquepts and Vertic Endoaqupts) of cultivated and adjoining uncultivated soils of south Urmia that have been under continuous horticultural practice for more than 5 decades were described and sampled. The soil samples were analyzed for different K forms and K adsorption properties after they were air-dried and ground to pass through a 2-mm sieve. The result showed that for most of the studied soils, continuous horticultural practices decreased the amount of different K forms as result of changes in soils types, agricultural practices and soil properties. Comparisons also showed that continuous horticultural practice significantly caused reduction in the all forms of K excluding the non-exchangeable K (NEK). Among the soluble K and NEK, respectively, showed the highest and the least changes. The continuous horticultural practice decreased 100 percent soluble K, 60 percent exchangeable K, 60 percent available K in the studied soil subgroups. Mineralogical studies also suggested that continuous horticultural practices caused changes in the relative intensity and position of the XRD pattern (peak) of illite and smectite.