Post-harvest foliar-applied Fe(II)-sulfate promotes Fe nutrition of pear trees grown in calcareous soil

Abstract

The effectiveness of post-harvest foliar-applied Fe(II)-sulfate was assessed and indices were tested for precocious prognosis of Fe-chlorosis in field-grown pear trees. In a commercial pear (Abbé Fétel/BA 29) orchard, Fe-induced chlorotic trees were sprayed in early autumn with a Fe(II)-sulfate heptahydrate solution and compared with water-sprayed control trees. Leaf Fe concentration was higher in senescent and abscised leaves of Fe-sprayed trees, indicating that Fe was taken up. However, phytotoxic symptoms occurred and leaves fell earlier than in untreated trees. Fe(II)-sulfate spray increased Fe concentration of flower buds and fruiting spur leaves as well as leaf Chl values. Yield was increased in sprayed trees by about 13%, mostly associated with a higher fruit number per tree rather than fruit size, indicating an improved fruit set. We hypothesize that a fraction of the absorbed Fe contributed to sustain Fe requirements of the newly formed organs as from growth resumption. Summer leaf SPAD readings were positively correlated with Fe concentration of flower buds, fruiting spur leaves and, in particular, with senescent and abscised leaves. Our findings suggest the effectiveness of the post-harvest foliarly applied Fe(II)-sulfate to improve Fe nutrition of pear trees the following season. Rather than inducing a temporary re-greening, our approach is based on the fact that high Fe-rates sprayed before leaf fall may contribute to increase Fe pools within perennial organs. We propose utilizing leaf Fe concentration of senesced and abscised leaves as a predictive tool for the diagnosis of the Fe-chlorosis occurrence in pear trees.