Nitrogen is the most commonly applied nutrient in orchard crops and is normally applied at higher rates than most other nutrients (Weinbaum et al., 1992). The effect of N on pecan yield and nut growth has been studied since 1918 (Skinner, 1922). Although N is a major component of pecan nutrient management, pecan tree response to N has been variable in multiple studies through the years (Hunter and Lewis, 1942; Smith et al., 1985; Storey et al., 1986; Worley, 1974, 1990).
Recently, rising energy costs have led to a dramatic increase in the price of synthetic fertilizer (Huang, 2009). Between 2002 and 2007 the cost of synthetic fertilizer N per acre rose by over 200% for pecan (Wells, 2009a). This sharp increase in the cost of a single input dramatically reduces the profit margin for pecan producers.
Overfertilization can be more common in orchard crops than in many other crop species as a result of the increased likelihood of fertilizer N application during the dormant period of perennial crops. Excess N increases vegetative growth, which promotes shading and reduces flower bud development, fruit set, quality, and survival. Excessive levels of applied N can also lead to nutritional imbalances and increased susceptibility to insect and disease pests (Weinbaum et al., 1992). Historically, N fertilizer has been uniformly broadcast on the soil surface in single or split applications of ≈84 to 168 kg·ha−1 N in southeastern pecan orchards. Fertigation has been used effectively in southeastern pecan orchards as well (Worley et al., 1995; Worley and Mullinix, 1996). Most pecan orchards in the southeastern United States are managed with a 3.7- to 4.6-m vegetation-free strip centered on the trees, which run the length of the tree row. Middles between tree rows are covered with grass and or a grass/legume mix. Thus, much of the fertilizer N applied to vegetated row middles could potentially be used by the vegetation growing there and, as a result, would theoretically provide little immediate benefit for pecan trees. Kulesza and Szafranek (1990) observed no difference in apple (Malus domestica Borkh.) tree performance when fertilizer was applied only to the vegetation-free strip compared with uniform application over the entire orchard area. Worley (1997) observed that pecan yield, quality, and leaf N could be maintained with dry fertilizer applications when the full N rate was concentrated in a limited area, yet no studies have attempted to refine this practice by simply eliminating excessive fertilizer applied to vegetated row middles, allowing only the fertilizer N applied in the vegetation-free strip to meet the tree’s N demand.
Application method and placement can improve the efficiency of applied N per unit of yield, potentially minimizing N loss and increasing the profit margin for pecan producers (Weinbaum et al., 1992). The objective of this study was to investigate the effects of N fertilizer application method and placement on pecan leaf tissue N concentration, pecan yield, nut quality, and pecan tree yield efficiency.
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