Blueberry (Vaccinium spp.) plants in Florida are typically grown on sandy soils where the risk of N loss via leaching is greater than on clay soils (Whitehead and Raistrick, 1993). Although cultivated blueberry grows optimally with ammonium as the N source, and ammonium is typically not as readily leachable as nitrate, significant leaching of both N forms occurs on coarse-textured sandy soils (Vitosh et al., 1995). In addition, the rainy season in Florida is from late spring through early fall, which coincides with the time when commercial blueberry growers apply N fertilizer. It is commonly understood that heavy rainfall increases N leaching (Gheysari et al., 2009; Wild and Cameron, 1980). In addition, blueberry plants are shallow-rooted, with roots concentrated mostly in the top 0.15 m (Williamson and Miller, 2009). Thus, there is a high risk for N leaching and an increased potential for ground or surface water contamination where blueberry is grown on sandy soils in humid, subtropical climates.
Split applications of N may extend the time of N bioavailability for plant uptake and have been reported to promote yield or plant growth compared with a single application. For example, mature blueberry plants had a 10% yield increase (Hanson and Retamales, 1992), red raspberry (Rubus idaeus L.) ended up with a significantly greater berry yield (Rempel et al., 2004), and lowbush blueberry (V. angustifolium) plants increased both growth and berry yield significantly (Percival et al., 2002).
Storage and remobilization of N in perennial woody species such as blueberry help plants reduce dependency on fertilizer N (Geßler et al., 1998; Millard, 1996). Remobilization of storage N accounted for ≈65% of the total N in new vegetative growth of ‘Climax’ rabbiteye blueberry (V. virgatum Ait.) at vegetative budbreak (Birkhold and Darnell, 1993). Cheng and Fuchigami (2002) found that 50% of reserve N in apple (Malus domestica Borkh.) trees was remobilized to support new growth of shoots and leaves. Some species of woody plants can remobilize up to 90% of reserve N to new leaf growth (Millard, 1996). Thus, with sufficient N storage, plants can be less dependent on N fertilizer. However, N remobilization is closely related to plant phenology (Millard and Grelet, 2010).
Banados (2006) concluded that N uptake in mature NHB (V. corymbosum L.) is more dependent on plant demand than on N availability in the soil. Thus, an effective N fertilization program requires a clear understanding of the times when N fertilizer is most needed. Previous studies have found that the effect of application date on N absorption by blueberry plants is significant (Banados, 2006; Hanson and Retamales, 1992; Throop and Hanson, 1997). However, these studies used the midseason NHB cultivar ‘Bluecrop’. Southern highbush blueberry (V. corymbosum L. interspecific hybrid) cultivars that are adapted to Florida’s mild winter climate ripen fruit earlier in the season and have a longer postfruit harvest vegetative growth period than NHB cultivars. Therefore, seasonal growth and N demand of SHB may differ from NHB. However, there is no literature available for the seasonal growth and N demand pattern of young SHB plants. This study was conducted to 1) determine seasonal growth of SHB by measuring organ DW at various growth stages, 2) identify the growth stages of young SHB that exhibit the greatest N uptake, and 3) determine N allocation patterns within plant tissues.
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