Abstract
The phosphate ions adsorption of some calcarious soils of Nainawa and Kirkuk regions from 0.01 M KCL solution containing (1-12) micromoles P has been studied .The different type of soils (32.4-39.84) % CaCO3 were fertilized with (22.5, 45, 90) kg P/ha and planted with maize ( Zea mays L. ) in 1 kg pots for five years. Adsorbed phosphorous at equilibrium solution concentration of 0.2 ppm P ( Ce = 0.2ppm P ) was determind .It was established an inverse relation between adsorbed P at Ce = 0.2 ppm P and the extractable phosphorous was established. The amount of adsorbed phosphorous at Ce = 0.2 ppm P diminished as the rate of applied fertilizers increase. From the data obtained in this study one may conclude that for the studied soils an average of 69.3 ppm extractable P correspond to an equilibrium soil solution of 0.2 ppm P ( Ce = 0.2 ppm P ) considered as adequate nutration level for most field crops, and justifies the use of P adsorption isotherms for evaluating the phosphorous fertilizer requirement.