Changes in Extractable Zn and P Applied as Organic and Inorganic Forms to a Certain Calcareous Saudi Arabian Soil

A greenhouse incubation study was conducted to investigate the extraction of Zn and P by Ammonium Biocarbonate - Diethyltriaminepentaacetic Acid (AB-DTPA) from a calcareous sandy loam soil that had been treated with ZnSO47H2O, KH2PO4 and/or poultry manure (PM). Extractable Zn from soil receiving Zn fertilizer increased rapidly within the first day of incubation, and decreased uniformly throughout the following 84-days. Extractable P from samples treated with P fertilizer showed the same pattern up to 54 days but increased thereafter indicating the release of a portion of the fixed P with elapsed time. Application of ZnSO4.7H20 decreased Fe and Cu and increased that of Mn. In contrast, addition of KH2PO4, increased extractable Fe and Mn, but decreased extractable Cu. Poultry manure (PM) addition decreased soil-pH and increased extractable Zn and P levels throughout the tested periods. The considerable increase in these nutrients was also attributed to the organic complexing agent in manure which most probably supplied chelating agents that kept nutrients in soluble and available form. Extractable Zn or P from soil amended with PM did not decline with time at the same rate as inorganic Zn and P which were added as fertilizers. The results obtained show that, poultry manure is a valuable source of nutrients with relatively long lasting effect on soil reaction and nutrients availabilit