In order to determine the critical level of phosphorus using the kate – Nelson method, economic outlook and the Mitcherlich equation in the rape dry farming of canola in Behbahan region, 16 experiments in four regions and each region in 4 experiments in four groups of soil, using phosphorus (less than 3 mg/kg, 3 to 6 mg/kg, 6 to 10 mg/kg and more, 10 mg/kg) in the form of randomized complete blocks design with four phosphate fertilizer treatments (0, 25, 50, 75 kg/h P2O5) from triple super phosphate source in four replications for two agricultural years (2008 to 2010) was implemented. In the experiment, Hyola 401 was used. The results showed that the critical level of soil phosphorus to Kate - Nelson, economic outlook and the equation Mitcherlich is respectively 7, 6, 9.4 mg/kg.
Key words: Kate-Nelsonl method, canola, the critical level, balanced fertilization.
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