Response of Olive Trees (Olea europaea L.) cv. Kalinioti to Nitrogen Fertilizer Application

Nitrogen is the most commonly managed mineral nutrient in olive groves because it is essential for plant growth. The precise management of N fertilization in olive cultivation is still not fully clarified, but it is essential for providing sustainable production. A nitrogen fertilizer experiment with olive trees (cv. Kalinioti) was carried out over a six-year period. Seven levels of nitrogen fertilizer given as ammonium nitrate (control, 1, 2, 3, 4, 5, and 6 kg/tree) were annually applied in order to determine the effect of nitrogen on vegetative growth, fruit set, fruit weight, yield, maturation index, and leaf N, P, and K concentrations. The results indicate that, under these conditions, application of up to 4 kg NH4NO3/tree significantly increased yield to 62.5 kg/tree compared to the control (37.09 kg/tree). The positive effect was attributed to the initial and final fruit set increases (7.63 and 3.73%, respectively at 4 kg NH4NO3/tree). However, the weight of 100 olives (W100 = 331 g) at 4 kg NH4NO3/tree obtained during harvest was considerably lower compared to the control (W100 = 384 g). Higher nitrogen rates decreased yield while increasing overall shoot growth. Nitrogen fertilization did not significantly influence the oil content of olive fruit. Fruit weight, maturation index, and concentration of oil reached maximum levels in the beginning of December, indicating a suitable start to olive harvesting. The concentration of N in olive leaves increased from 1.23% to 2.38% as fertilizer levels increased from 0 to 6 kg NH4NO3. Maximum yield was achieved at a level of 6 kg NH4NO3/tree, which corresponded to 2.01% N in leaves. The results suggest that application of 3 kg NH4NO3/tree can be recommended for table olive production, due to the fact that fruit weight was not decreased, while fertilization with 4 kg NH4NO3/tree was suitable for oil olives.