Towards a new interpretation of soil P-test values in Geneva for the fertilization of winter wheat | Nouvelle interpretation des teneurs en phosphore pour les sols genevois
2007
Besson, A. | Muller, J. | Gillet, A.,Ecole d'ingenieurs de Lullier, Jussy (Switzerland)
The current interpretation of soil P-test values could be modified in light of results collected in the Geneva canton. Considering the median P values obtained for soils containing 20 to 40% clay with pH ≥7, significantly different interpretations can be provided, according to the considered reference values. The observed discrepancies are related to inconsistencies in the references values rather than in the extraction procedure. Furthermore, the analysis of the data collected in the Swiss French network of farms revealed that the wheat yield is not increasing in soils with a P-AAEDTA content of 50-75 mg/kg compared to soils with a P-AAEDTA content of 25-50 mg/kg upon a 25 kg/ha P input. This result suggests that the recommendable P value could be fixed lower than the present 50-75 mg/kg content proposed by the "basic data for fertilization in Switzerland" (DBF). Finally, the results of two field experiments conducted in 2001 and 2002 show that, accounting for wheat variety and field history, a good correlation (r2 = 0.70) between the P-AAEDTA content of the soil and total P in the aerial parts of wheat at Zadoks stage 31-32 is observed. These experiments also showed that the P content of the soils, although smaller than the recommended values, was most likely not the yield limiting factor. As a consequence, we suggest to recommend a P-AAEDTA value in the 25-50 mg/kg range for winter wheat on soils containing 20 to 40% clay with pH ≥7.
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