Tree size and flowering intensity as affected by nitrogen fertilization in non-bearing orange trees grown under Mediterranean conditions

A field experiment was conducted in the South of Portugal with young (0-3 years old) non-bearing ‘Lane Late’ orange trees. Five nitrogen (N) rates were used in a randomised block design with three replicates. The 180 g N tree^?1 over three years led to the greatest canopy width (176 cm) and volume (2,697 dm³). The greatest rate applied (720 g N tree^?1 in the three years) led to the largest flower yield. Nitrogen concentration in the flowers significantly increased with fertilizer N, and also with the flowering period up to the 23^rd day, declining thereafter. Flower yield was strongly correlated (r = 0.99, p < 0.001) with flower N concentration. Nutrient composition of flowers and of mature leaves from the spring flush was compared. Significant correlations were found for N (r = 0.47, p <0.01), P (r = -0.49, p <0.01), K (r = 0.44, p <0.05) and Ca (r = 0.87, p <0.001), suggesting that flowers can be used as a tool to diagnose the nutritional status of trees. Canonical analysis (with N treatment as dummy-variables) showed strong relationships between canopy width and N, which were greater at the larger rates of fertilizer application, and strong and inverse relationships between K and Mg, also with the greatest N rates.