Use of thermodynamic parameters of q−i isotherms to evaluate of k−availability in some Egyptian soils

الملخص EN

  Quantity−intensity (Q/I) isotherms were applied to evaluate the availability of K⁺ in four different Egyptian soils.

Wheat plant was used as an indicator to achieve this goal.

After wheat sowing, soils were fertilized by K₂SO₄ at different rates of 0, 50, 100 and 150% of wheat's fertilizer recommendation.

The obtained results showed that increasing added K⁺ concentrations led to increase the activity ratio of K⁺ (AR_K⁰) and corresponding changes in labile K⁺ (K) at equilibrium.

The equilibrium activity ratio of K⁺ (AR_K⁰) varied between 2.88 − 15.01 × 10⁻³ (mol L⁻¹)^0.5 in initial stage and 1.39 − 17.31 × 10⁻³(mol L⁻¹ )^0.5 in the last stage.

The labile K⁺ (K_L) fraction ranged from 0.047 − 0.456 and 0.02 − 0.45 cmol kg⁻¹ before sowing and at harvesting time of wheat plant, respectively.

The potential buffering capacities of K⁺ (PBC_K) fluctuated from 16.3 − 30.4 and 11.9 − 29.9 cmol kg⁻¹ (mol L⁻¹) ^−0.5 before sowing and at harvesting stage of wheat plant.

The free energy of K⁺ exchange (−ΔG) ranged from −3.37 to −2.42 (kcal.

mol⁻¹) prior to cultivation to reach −3.79 to −2.34 (kcal.

mol⁻¹) at the end of cultivation period.

In general, Silt, pH, EC, OM, Soluble K, NH₄OAcK and HNO₃K exhibited substantial correlations with K_L, PBC_K, AR_K⁰, K_G and ΔG, whereas pH had inverse correlation with mentioned parameters, except K_G.

Furthermore, a substantial correlation was observed between thermodynamic characteristics of K extracted by H₂O, 1 M NH₄OAc and 1M HNO₃.

 Conclusively: from these results it could be concluded that, significant correlation of the tested thermodynamic parameters with physicochemical soil characteristics.

Thus, the study contributed significantly to practical K⁺ management by providing important information on K⁺ dynamics in typical Egyptian soils.