Phosphorus Availability in Relation to Inorganic P Forms and Soil Properties of Saudi Arabia Calcareous Soils

Abstract

Fractionation of inorganic P was carried out in 66 surface soil samples representing calcareous soils of Saudi Arabia. Chemically available P was also determined using six different extracting methods. Simple correlation coefficients were calculated to correlate chemically available P in different methods of extraction with various inorganic P forms. Also, stepwise linear regression was carried out to predict the contribution of various inorganic P forms as well as other soil properties such as pH, CaCO3 content, clay content, extractable Ca, Mg and Na and micro-nutrient content, to the significance of the soil P test by six different methods of P-extractions. Results indicated that available P determined by different methods increased in the order Bray no. 1 > Morgan > Colwell > Olsen > AB-DTPA > H20. The Ca-P, Fe-P, Al-P and Sol-P constituted on the average 92.0, 2.4, 1.8 and 0.3% of the inorganic P. Available P extracted by Olsen, Colwell, AB-DTPA and Bray no.1 methods was well correlated with Al-P, and Fe-P. The weakly acid Morgan extractant (pH 4.2) was the only soil test which correlated with Ca-P form. The values of P extracted by Olsen, Colwell and AB-DTAP methods were significantly correlated with each other due to the similarity of the P forms extracted by these methods. Al-P contributed most to phosphorus extracted by the methods of Olsen and Colwell