Potassium Fixation and Charge Characteristics of Soil Clays

Abstract

Forty‐four soil clays and four reference phyllosilicate clays were used to establish qualitative and quantitative relationships between clay mineral characteristics and K fixation. The soil clays were obtained from Vertisols, Vertic Mollisols, Haploxerolls, Xerochrepts, and a Palexeralf, from three semiarid regions of northwestern Morocco. The soil clays contained beidellite, montmorillonite, vermiculite, and illite in widely varied abundances. Both total and tetrahedral cation‐exchange capacity (CEC) were measured. Octahedral CEC was calculated by difference. Tetrahedral CEC was determined after saturation with Li and heating at 300 °C to reduce octahedral charge to near zero. Potassium fixation was determined in both wet (1:4 soil/solution, 16 h on a shaker) and dry conditions (after drying for 24 h at 70 °C) using three different levels of added K. Total CEC was well correlated with tetrahedral CEC (r2 = 0.76, P < 0.001). About half of the smectitic and vermiculitic soil clays have >50% of their total charge due to tetrahedral charge. The amount of K fixed Increased with added K, whereas the percent K fixed relative to total added K decreased. The K fixation by the clays studied was best correlated with total CEC for a given amount of K added. It was also well correlated with tetrahedral CEC. Simple regression analysis did not show any significant effect of octahedral CEC. A multiple regression analysis, however, demonstrated that both components of total CEC, tetrahedral and octahedral, have a simultaneous effect on K fixation. Tetrahedral CEC explained more of the variation (64%) than octahedral CEC (36%). This greater effect was attributed mainly to the proximity of tetrahedral charge to the interlayer space of 2:1 phyllosilicate clays.

Bioavailability and mobility of Pb after soil treatment with different remediation methods

“…In these tests, we used vermiculite as a carrier material for Slovakite and apatite, since vermiculite has a high water retention capacity. However, vermiculite also exhibited a substantial Pb sorption property (Table 2), presumably due to its high positive surface charge (Bouabid et al 1991). The sorption of Zn 2+ and Cu 2+ from the water solution by Slovakite in vermiculite was also higher than by apatite in vermiculite (data not shown).…”

Factors affecting potassium fixation in seven soils under 15-year long-term fertilization

“…The clay mineral types, pH, soil organic matter (SOM), hydroxide aluminum, soil moisture status, cation exchange capacity (CEC), fertilization, and tillage system are the major factors affecting the equilibrium [4][5][6][7][8][9][10][11][12][13] . Those factors on soil K fixation have been studied by various short-term experiments.…”

Potassium Fixation by Oxidized and Reduced Forms of Phyllosilicates

“…Negative charge originating from the tetrahedral sheet retains cations more strongly than equivalent negative charge originating from the octahedral sheet due to the proximity of the charges to the interlayer surface (Reid-Soukup and Ulery, 2002). In a study using 44 soil clays, three montmorillonites, and one vermiculite, K + fixation capacity was found to be best correlated with total layer charge, well correlated with tetrahedral cation exchange capacity, and poorly correlated with octahedral cation exchange capacity (Bouabid et al, 1991). This is likely a function of interlayer cations being attracted to both tetrahedrally and octahedrally derived charge, but more so to tetrahedrally derived charge due to its proximity to the interlayer surface.…”

“…However, it is difficult to determine to what degree any extraction procedure truly removes solution and exchangeable K and leaves fixed K. Multiple washes recover more K than single washes (Pratt et al, 1956), but there is no consensus on how many washes are appropriate to use. One to five washes are typically used (Stanford, 1947;Mortland and Gieseking, 1951;Wear and White, 1951;Bouabid et al, 1991), but there is generally no rationale presented behind the use of any number of washes. We chose to use five with the thought that we did not want to mistakenly leave behind solution or exchangeable K and interpret it as fixed K. We also individually measured the K concentration of each wash.…”