Wheat P requirement on calcareous Moroccan soils: II. As estimated by the olsen P soil test and plant uptake

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Abstract
Dry matter wheat [Triticum aestivum (L.)] yield was dependent (R2 - 0.57) on plant P concentration and also related to plant P uptake (R2 - 0.78). Plant P uptake equalization, after P fertilization, for the 15 soils in this region of Morocco appear to be a function of differences in plant P concentration. The relative yield when regressed on Olsen extractable P was significantly fitted (R2 = 0.86) to the Mitscherlich-Bray mode. Plant P uptake regressed on Olsen P, including all soils, best fit a second degree polynomial (R2 - 0.57). Including soil P buffer capacity, oragnic matter and pH improved this fit to R2 - 0.77. Fertilizer p requirements necessary to obtain the Olsen extractable P level for 90% relative yield was lower using the nonlinear estimation than by log transformation. For these soils these differences were small and for practical puposes either method could be used to interpret the P fertilizer requirement directly form Olsen extractable P, depending on the computer and software available.