Abstract
Sodium quantity/intensity curves were applied for exchangeable isotherm system Na+ - Ca+2 suggested by Beckett by using thermodynamic parameters to evaluate fertility status in some rain-fed soils in Nineveh province / northern of Iraq. Results indicated that all studied soils were of neutral pH with appreciable total and active carbonates content of 182-270 , 63-91 gm.Kg-1 respectively, with dominant of chloritized semictite and illite clay minerals in soils clay fraction. the values ranged widely from 0.25×10-3 - 0.94 ×10-3 mole.L-½, the labile pool of potassium values ranged from 10.91-25.36 c.mole Kg-1 , while sodium potential capacity values from 24.76- 42.18 c.mole.(Kg.mole-1)-½.. On the other hand Gibbs free energy values- ∆G were negatively spontaneous reactions and ranged from -7.91 to - 0.6 cal. mole-1 and Gapon selectivity coefficient values ranged between 1.32 - 2.99 L.mole-1. Lacked in the curvature commonly seen in the quantity/intensity curves for sodium. Result showed lower values and higher energies of replacement of calcium by sodium, also showed a higher affinity for than . They also indicated that Na held in these soils in two characteristics types of exchange sites having different affinities for sodium.
