Olive oil production is historically important throughout the Mediterranean where there is evidence of human cultivation and consumption from as far back as 5000–6000 years ago (Vossen, 2007). Today the world has some 9.4 million ha of orchards producing 1.5 million tons of table olives and 16 million ton of olives that are processed into 2.56 million tons of oil (Vossen, 2007).
Olives are commonly propagated by leafy cuttings under mist (Peixe et al., 2007). Factors that may affect rooting rate of cuttings include: type of wood used, season, and cultivar. Rooting rate is highest from April to October (northern hemisphere) and cutting shoot growth is maximal during June to July. In winter, rooting rate and shoot growth are reduced (Fabbri et al., 2004). Cultivars differ widely in their ability to root. Some varieties produce roots from cuttings easily, whereas others are very difficult to root. The Greek ‘Kalamata’ (Sutter, 2005), the Tunisian ‘Chemlali De Sfax’ (Fabbri et al., 2004), the Spanish ‘Gordal Sevillana’ (Gonzalez Padilla et al., 2009), the Portuguese ‘Galega vulgar’ (Peixe et al., 2007), the Italian ‘Leccio del Corno’ (Bartolini et al., 2008), and the ornamental ‘Swan Hill’ (Sutter, 2005) are understood to be difficult-to-root cultivars. In such cultivars, grafting, despite its expense, can be the main method for propagation. One of the factors influencing rooting rate of cuttings of evergreen trees is stock-plant mineral nutrition (Blazich et al., 1988). Several studies evaluated the effect of fertilization regime (mainly regarding N) of stock plants on propagation rate. Henry et al. (1992) studied the Eastern Redcedar, Raymer et al. (2008) studied the Seacoast Marshelder, and Rowe et al. (1999) evaluated the response of the Loblolly Pine. In general, but not always, higher N supplied to the stock plant resulted in lower propagation success. However, no such evaluation has been determined for olives. The global production of olive seedlings currently stands at ≈40 million trees per year (Fabbri et al., 2004). This number is on the rise as a result of the expansion of olive cultivation and the increase in average tree density in orchards (De la Rosa et al., 2007). Increasing the rooting rate, especially in those cultivars that are difficult to root, would lower costs in the nursery and lower the price of seedlings. The objective of this study was, therefore, to investigate the manner in which N, P, and K fertilization of stock plants affects the propagation rates of rooted olives.
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