ASSESSING THE NITROGEN NUTRITIONAL STATUS OF YOUNG NON-BEARING 'ROCHA' PEAR TREES GROWN IN A MEDITERRANEAN REGION BY USING A CHLOROPHYLL METER

摘要

To find an alternative tool to chemical analysis for assessing the nitrogen (N) nutritional status, the SPAD-Minolta-502 portable chlorophyll meter was tested in one- to three-years-old 'Rocha' pear trees fertilized with 0, 10, 20 and 40 kg N ha-1 year-1. SPAD readings in the third and fourth fully expanded leaves were as responsive to N fertilization as leaves sampled for foliar chemical analysis (medium third of one-year-old shoots), but individual leaves showed heterogeneous chlorophyll patterns. SPAD readings in leaves sampled at 60 and 110 days after full bloom (DAFB) related linearly with leaf N concentration but significant relationships could also be obtained later. Assuming an optimum leaf N concentration of epsilon 20 g kg-1 dry weight, SPAD readings epsilon 33 in leaves sampled at 60-110 DAFB corresponded to a good nutritional N status of young pear trees, making this diagnostic technique more practical, non-destructive and inexpensive, compared with chemical leaf analysis.