The Effect of Ionic Strength And Soil Properties in Phosphorus Adsorption in Some Calcareous Soils

Abstract

Laboratory experiment conducted for studying the effect of ionic strength and soil properties in phosphorus adsorption in some Calcareous soils. In this experiment, ten soil sites from different parts in Basrah governorate were collected. These soils were collected from sites as follows: Al-Brazeia, Tanuma, Najibia, Al-Hartha, Al-Deir, Al-Qurna, Al -Fao, Al-Berjesia, Am-Qaser and Khor Al-Zbeir. The laboratory work is done by weighting 2.5 g. from each soil and put them in 50ml conical flask. Then added phosphorus in the form of phosphate mono potassium KH2PO4 on nine levels as follows: (0, 50, 100, 150, 200, 250, 300, 350, 400) µM L-1. As well , it was used three levels of waters (control (distilled water), 0.1 mol L‾¹ NaCl and 0.2 mol L‾¹ NaCl). The water was added to each treatment to field capacity. Meanwhile, the treatments were shake and left till equilibrium. After that procedure, it was determined the soluble phosphorus after equilibrium and calculated adsorbed quantity of phosphorus on the soil surfaces. The results are tested by linear Langmuir equation and calculation the constants of this equation, (b, k). The results showed that the increase of added water salinity to the soil leads to increase of phosphate adsorption by fine textured soils like silty clay loam and silty clay whereas phosphate adsorption decreased in coarse textured soils like loamy sand and sandy ones and this go in line with adsorption curve where coefficient of correlation was L =0.0026 – 0.854 for all studied treatments. The soil colloids (clay, silt), solid carbonate and soil salinity gave high significant coefficient of correlation (r) with adsorption maxima of phosphorus (b) and with bonding energy constant (k).