Potato (Solanum tuberosum L.) tubers continue active metabolism after harvest and require appropriate storage conditions to minimize losses that can arise from these physiological processes (Kumar et al., 2004). One key factor determining storability of tubers is harvest maturity, classified as physical, physiological, and chemical maturity (Bussan, 2003). Tablestock potatoes reach harvest maturity when the tuber periderm adheres firmly to the underlying cell layers, the point known as skin-set (Lulai and Orr, 1993). Early-season tablestock cultivars are often grown as a spring crop to meet an early market window with high prices; however, they are typically harvested 90–120 d after planting (DAP) at which point the periderm is minimally mature and easily removed (UNECE Standard FFV-52, 2011). Greater quantitative and qualitative losses are associated with storage of immature tubers (Burton, 1989) whereas tubers harvested from senescent plants are physically more mature (Braue et al., 1983). For this reason, tablestock potato vines are killed before harvest to promote periderm physical maturity (“skin-set”), thereby reducing skinning or scuffing during mechanical harvest and subsequent handling operations (Zotarelli et al., 2016b).
Water and nitrogen availability during plant growth can affect leaf growth and carbon partitioning, and subsequently the biochemical process involved in tuber skin-set (Tyner et al., 1997). Northeast Florida accounts for the majority of the state’s spring potato production, characterized by fine sandy soils with low water-holding capacity and low organic matter content (Manrique, 1993). Heavy and erratic rainfalls commonly experienced in such subtropical growing regions can cause nutrient leaching from the root zone, further decreasing available nitrogen (Papadopoulos, 1988). Acceptable tuber yields and quality are also dependent on the placement and timing of NF (Westermann et al., 1988).
The current grower practice in northeast Florida is band application of granular NF at preplant (≈30 d before planting), at plant emergence (25 DAP), and at the onset of tuber initiation (Rens et al., 2015). There is rapid nitrogen uptake 45–65 DAP (Zotarelli et al., 2014, 2015b), during which time the risk of leaching is also high. Seepage irrigation is the primary method used in this region and requires maintenance of a high water table. This method also has the potential for increased nutrient leaching and runoff, and has raised important ecological and human-health concerns in this growing region, where groundwater is the source of drinking water for most of the residents. By contrast, fertigation delivers dissolved fertilizer through drip tapes that increases water and nutrient use efficiency by precisely applying water and nutrients to the plant root zone. Reyes-Cabrera et al. (2014) also reported significant decreases in tuber physiological disorders for early-maturing potatoes grown using fertigation.
A companion study of early-maturing, tablestock potatoes grown in sandy soils found that fertigation obtained maximum yields by applying nitrogen at rates 224–273 kg·ha−1 (Makani et al., 2015). However, excess NF negatively affects plant and tuber growth by promoting excessive vine growth and by delaying tuber periderm maturation in the field, leading to higher weight loss (Dahlenburg et al., 1990), higher disease incidence (Jablonski, 2006), decreased phytochemical content (Zhang et al., 1997), and low or elevated starch content (Bombik et al., 2002). It is important to note that these studies were conducted using medium-to-late season cultivars that have more mature tuber periderm at harvest because of a longer growing season (up to 180 d). Consequently, adoption of NF recommendations based on these cultivars could potentially cause significant storage losses to the more perishable, early-maturing potato cultivars.
The objective of this present work was to determine the effect of growing two commercially important, early-maturing potato cultivars using two NF application methods, four NF rates, and three harvest intervals after vine killing on selected tuber quality and nutritional value parameters at harvest and during simulated commercial storage.
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