Spatial Heterogeneity of Soil Silicon in Ukrainian Phaozems and Chernozems

This study investigated the spatial variability of the soil silicon content in relation with topography, parent materials, soil texture, soil organic matter, exchangeable cations and pH. Using the experimental data from two longterm sites in the Forest-Steppe area of Ukraine, the SiO 2 content was estimated in 60 samples taken from a soil depth 0-25 cm. The accumulation of SiO 2 was significantly greater in the soils formed in footslopes. A content of extractable silicon fraction significantly increased from a sandy loam-(366-465 mgkg -1 ) to medium-(670-697 mgkg -1 ) and heavy-(506-849 mgkg -1 ) textured soils. The highest amount of available silicon content was found in the soils containing: 35.0-39.9% of physical clay fraction (< 0.01 mm dia) in Hrytsiv area -143.0 46 mgkg -1 and < 25.0% of physical clay fraction in Khrolyn area -125.0 6 mgkg -1 . A significant relationship was found between pH KCl , P 2 O 5, K 2 O, Mg and both forms of SiO 2 . There was almost no correlation between available/ extractable SiO 2 and exchangeable Ca and Ca+Mg. Our studies found the best correlation between extractable SiO 2 and spring barley yield (r = 0.651; P = 0.041), as well assoluble SiO 2 and corn for grain yield (r = 0.514; P = 0.128). No significant relationships were found for sugar beet, winter wheat, sunflower.