动力学模型在土壤钾素释放特征描述中的运用及其与化学方法提取的钾素之间的相关性研究

Application of kinetic models in describing soil potassium release characteristics and their correlations with potassium extracted by chemical methods

Potassium (K) release characteristics in soil play a significant role in supplying available K. Information on K-release characteristics in soils of central Iran is limited. The objectives of this study were to determine K release characteristics and correlations of K release rate constants with K extracted by different chemical methods in surface soils of ten calcareous soils of central Iran. The kinetics of K release in the soils was determined by successive extraction with 0.01 mol L^-1 CaCl₂ in a period of 2--2 017 h at 25±1 ^oC. Soil K was extracted by distilled water, 0.5 mol L-1 MgNO₃, 0.002 mol L^-1 SrCl₂, 0.1 mol L^-1 BaCl₂, 0.01 mol L^-1 CaCl₂, 1 mol L^-1 NaCl, 1 mol L^-1 boiling HNO₃, 1 mol L^-1 NH₄OAC, Mehlich 1, 0.002 mol L^-1 SrCl₂ 0.05 mol L^-1 citric acid, and ammonium bicarbonate-diethylenetriamine pentaacetic acid (AB-DTPA). A plot of cumulative amounts of K released showed a discontinuity in slope at 168 h. Thus, two equations were applied to two segments of the total reaction time (2--168 and 168--2017 h). Cumulative amounts of K released ranged from 55 to 299 mg kg^-1 in 2--168 h and from 44 to 119 mg kg^-1 in 168--2 017 h. Release kinetics of K in the two time segments conformed fairly well to parabolic diffusion, simplified Elovich, and power function models. There was a wide variation in the K release rate constants. Increasingly higher average concentrations of soil K were extracted by distilled water, Mehlich 1, SrCl₂, CaCl₂, SrCl₂ + citric acid, AB-DTPA, MgNO₃, NaCl, NH₄OAc, BaCl₂ and HNO₃. Potassium release rate constants were significantly correlated with K extracted. The results of this study showed that information obtained from mathematical modeling in two reaction time segments can help to estimate the K-supplying power of soils.