Mature trees of Stark Redgold nectarines grown in silt loam soil in the Po Valley were tested at five fertilization regimes and compared to untreated control: N1 (100 kg N/ha), N1 (100 kg N/ha, split 60% in spring and 40%. in postharvest), N2 (200 kg N/ha), N1 (100 kg N/ha) + K (150 kg K2 0/ha), N2 (200 kg N/ha) + K (150 kg K2 O/ha). The annual distribution in spring was equally split before full bloom and at fruit set.
The data collected over the three trial years show no differences as compared to control in yield and fruit size. N2 delayed ripening and decreased fruit quality. Leaf mineral composition was affected by potassium; maximun N induced leaf accumulation of N-NH4 The high concentration of K in leaf tissues was correlated to the yellow color of the leaf blade. Total leaf chlorophyll content was measured by an Spad-502 chlorophyll meter (Minolta Corp.) and compared to that measured by conventional technique (Arnon method). The overall findings suggest the amount of N used in peach fertilization can be reduced.