Rape Response To A Syrian Phosphate Rock And Its Mixture With Triple Superphosphate On A Limed Alkaline Soil

A greenhouse experiment was conducted to evaluate the agronomic effectiveness of a Syrian phosphate rock (PR) and its mixture with triple superphosphate (TSP) (at a P ratio = 50:50) for rape (Brassica napus L.) grown on an alkaline soil (pH 7.72). The P rates applied were 0, 12.5, 25, 50, and 100 mg P kg(-1) as TSP or Syrian phosphate rock. Lime was applied at rates of 10%, 20%, and 30% of CaCO3 to evaluate rape response under alkaline and calcareous conditions. For the PR+TSP mixture, the same rates were used except for 12.5 mg P kg(-1) that was not included. The rape was grown to flowering stage for 85 days before harvest. The dry-matter yield obtained with each source was fitted to a semi-log response function that was used to assess the effectiveness of each P source under different liming conditions. The relative agronomic effectiveness (RAE) of PR and the mixture, PR+TSP, with respect to TSP was calculated as the ratio of the slopes of the response function. The results showed that the RAE values of Syrian PR were 55%, 42%, 26%, and 19% for soil treated with, 0%, 10%, 20%, and 30% of CaCO3, respectively. The corresponding RAE values of the PR+TSP mixture were 101%, 101%, 98%, and 97%, respectively. The results of P uptake by rape showed that the effectiveness followed the order of TSP greater than or equal to (PR + TSP)>PR.