Rape response to a Syrian phosphate rock and its mixture with triple superphosphate on a limed alkaline soil
1999
Habib, L. | Chien, S.H. | Carmona, G. | Henao, J.
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 CaCO(3) 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 CaCO(3), 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.
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