Kinetics of non-exchangeable potassium release in selected soil orders of southern Iran

Abstract

Non-exchangeable K release can greatly influence soil K fertility. This study was carried out to study the release of non-exchangeable K from 22 surface and subsurface soils of southern Iran using successive extraction with 10 mmol/l of CaCl<sub>2</sub> and oxalic acid in a period of 2−1368 h at 25 ± 1°C. Alfisols, Aridisols, Entisols, Inceptisols, Mollisols, and Histosols were among the studied soil orders. Illite, smectite, chlorite, vermiculite, kaolinite and palygorskite clay minerals were identified. The amount of non-exchangeable K varied from 95 to 506 mg/kg. Results showed that CaCl<sub>2</sub> and oxalic acid released 60 and 55% of non-exchangeable K from soils, respectively. The discontinuity in slope was found when the cumulative amount of released K was plotted versus time, supporting the multi-reactive nature of K exchange sites. The cumulative K release in soils ranged from 87 to 300 mg/kg for CaCl<sub>2</sub> and 78 to 300 mg/kg for oxalic acid which was well described by simplified Elovich and power function equations. The b constant of simplified Elovich as an index of non-exchangeable K release rate was in the range of 10 to 36 mg/kg for CaCl<sub>2</sub> and 11 to 36 mg/kg for oxalic acid. The highest b constant was measured in Inceptisols and Alfisols, while the lowest values were found in Entisols and Histosols. In conclusion, the K release pattern was similar for both extractants and affected by clay content and type, and soil depth.

Potassium adsorption capacity and desorption kinetics in soils of Qenberenaweti sub-watershed, central highlands of Ethiopia

“…The variation in the rates of K desorption in different soils indicates that the cations retained on the surface sites influenced the rate of K desorption [ 96 , 97 ]. According to Refs.…”

“…The constants ‘a’ and ‘b’ of each model represent the intercept and the slope of the linear curves obtained by plotting the released K against time. The constant ‘a’ represents the initial amount of K released [ 97 , 111 ] which shows the amount of equilibrium K initially available for plant uptake [ 111 , 112 ]. The constant ‘b’ reflects the release rate of the non-exchangeable K [ 97 , 111 ].…”

“…The constant ‘a’ represents the initial amount of K released [ 97 , 111 ] which shows the amount of equilibrium K initially available for plant uptake [ 111 , 112 ]. The constant ‘b’ reflects the release rate of the non-exchangeable K [ 97 , 111 ]. Thus, the ‘b’ value is known to correlate well with K + for plant uptake [ 113 ].…”