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

Abstract

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.

Acknowledgments

The author acknowledges support of the Washington Tree Fruit Research Commission and the Winter Pear Control Committee of the Northwest Pear Bureau, and to Dr. S. R. Drake for assistance in statistical analysis and to D. Burkhart for locating P-deficient soils in Oregon. Level of significance for correlation coefficients is indicated where ^* =0.05, ^{* *} =0.01, ^{* * *} =0.001, and ns=not significant.