Abdolkarim Ejraei - Department of Soil Science, college of Agriculture, Khorasgan (Isfahan) Branch, Islamic Azad University, Isfahan, Iran.
Ahmad Mohammadi Ghehsareh - Department of Soil Science, college of Agriculture, Khorasgan (Isfahan) Branch, Islamic Azad University, Isfahan, Iran.
Mehran Hodaji - Department of Soil Science, college of Agriculture, Khorasgan (Isfahan) Branch, Islamic Azad University, Isfahan, Iran.
Ali Asghar Besalatpor - Department of Soil Science, College of Agriculture, Vali-e-Asr University of Rafsanjan, Rafsanjan, Iran.

Several methods have been proposed for recommendation of phosphorus fertilizers. Each of them only examines the concentration of phosphorus in the soil or plant, while none of them investigates the correlation between phosphorus concentrations in the soil and plant. In this study, a method called integrated plant and soil system (IPSS) is proposed to describe phosphorus fertilizer. In this system, for recommendation of phosphorus, the correlation between this element in soil and plant was used. For this purpose, 39 Washington Navel Orange orchards were selected in Jahrom region and from each orchard three trees were chosen. Samples were taken from soil and plants during two consecutive years and their phosphorus was measured. Orchards were divided into two categories, first group high-yield orchards and another includes all orchards. The correlation was run between soil properties and phosphorus of plant organs with the phosphorus of soil saturation extract samples. Factors were selected that shown significant correlation with the phosphorus of soil saturated extract, and multivariate regression was established between them. The results showed a significant correlation between phosphorus of plant organs and soil samples, and the highest correlation was observed between fruit phosphorus and phosphorus of soil saturation extract. Moreover, there was a significant correlation between phosphorus of plant organs, and the highest correlation was observed between fruit phosphorus with other plant organs. A equation was also obtained for each of the two orchard groups, these two equations can calculate the amount of phosphorus required for orange orchards.

Fertilizer recommendation, Phosphorous, Regression model, Washington Navel orange