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Phosphorus deficiency symptoms in leaves of apple and pear trees as influenced by available soil phosphorus

The relationship between fruit tree condition, leaf phosphorus (P), and available soil-P content has been inadequately addressed as evidenced by different results in various parts of the world. This study attempts to provide additional information on P deficiency symptoms of apple and pear trees and its relation to leaf P and available soil-P content. This study also endeavors to establish and further verify the minimum available soil-P and leaf P concentrations required for healthy apple and pear trees, particularly in the Pacific Northwest. Purplish-red leaf margins indicating high anthocyanin production due to phosphorus (P) deficiency were observed in leaves of apple (Malus domestica) and pear (Pyrus communis) trees that were grown in low-P soils in the greenhouse or in the orchard. In one of the greenhouse apple experiments, as leaf P concentrations increased in ‘Delicious’ apple leaves from 0.083 to 0.153%, the incidence of purplish-red leaf margins decreased from 95 to 4%, respectively, (r2=−0.908). Observations of purple leaf margins from apple and pear trees in Pacific Northwest orchards were less obvious but positive trends were established between available soil P and leaf P. In general, the data suggests that available soil P (NaHCO3 method) and leaf P concentrations should be above 13 ppm and 0.13% P, respectively, for healthy apple and pear trees in the orchard for conditions in the Pacific Northwest.