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 23rd 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.