S Mahbob Sharemi, A Forghani, H Ramezanpor,
Volume 13, Issue 49 (10-2009)
Abstract
Surface charge of soils is measured using two different approaches: ion adsorption and potentiometric titration. Most models of surface charge chemistry of soils have been derived from the data obtained by potentiometric titration. The Uehara and Gillmanُs model was used to estimate the surface charges at some soil pH range in three forest soils of Lahidjan region. The selected soils (Typic Udorthent, Typic Hapludalf, Ultic Hapludalf) were formed on three different types of parent rocks. So, the effect of parent rocks on surface charge characteristics was investigated. Soil samples were characterized through their organic carbon, clay percentage, pH in water and 1 M KCl, cation exchange capacity (CEC), point of zero charge of variable charge components (pH0), zero point of net charge(ZPNC) and charge variation. All soils had a significant amount of negative charge at soil pH. A Typic Hapludalf contained the lowest value of pH0 and the largest amount of negative charge at soil pH. The pH0 values were less in the surface than in the subsurface horizons. The ZPNC values were not obtained by the interpretation of charge variation curves and estimated lower than 2.5, which refers to high amount of negative charge in these soils. Differences in negative charge development in a pH range from 3 to 6 were largest for horizons rich in organic carbon and least for those with significant amounts of layer silicate minerals. Data obtained from charge variation curves of the studied soils also showed that the values of AEC were low and below 1 cmol/kg soil.
A.r Hosseinpur, M.r Panahi,
Volume 14, Issue 52 (7-2010)
Abstract
Potassium (K) fixation by phyllosilicates clay minerals is a very important process influencing the availability of K for plants. Information about K fixation is limited in Hamadan soils. The objectives of this research were to determine potassium fixation capacity (PFC) and potassium fixation index (PFI) of 10 surface soils of Hamadan province and the correlation of these parameters with soil charge characteristics. Potassium fixation capacity was obtained using six different levels of added K as KCl and three wetting and drying cycles. Also charge characteristics of soils were determined. Tetrahedral CEC of soils was determined after saturation of samples with LiCl and heating at 300 oC to reduce octahedral charge near zero. The results showed that tetrahedral and octahedral CEC ranged from 4.6 to 16.0 and 0.8 to 4.9 cmolckg-1 respectively. Mineral and organic portion CEC ranged from 6.1 to 20.9 and 0.97 to 9.7 cmolckg-1 respectively. The amount of PFC increased with increasing added K. Mean amount of PFC ranged from 58.2 to 175.03 mgkg-1. Potassium fixation index ranged from 0.23 to 0.67. The results of correlation studies indicated that PFI were significantly correlated with octahedral CEC, mineral and organic portion CEC, total CEC, exchangeable and nonexchangeable K. The results of this research showed that PFI very different in soils. So that this parameter should be consider in K soil testing.
