The N status of persimmon trees is usually appraised by N concentration determined from midshoot leaves of late July to mid-August. Laboratory determination for leaf N concentration is time-consuming, and the results of such analyses are mostly used for N fertilization program of the next year in Korea. Under orchard situations in which tree vigor is less than desired, making a quick decision for supplemental N becomes more important throughout the current season. Because the traditional diagnostic techniques are useful mostly for the next season, the necessity arises for rapid N diagnosis for the current season. Growers often use leaf “greenness” as a visual indicator of the need for supplemental N. However, the degree of greenness is quite subjective; different people perceive it differently. A quicker and quantitative method is thus needed.
The SPAD-502 chlorophyll meter has been successfully used in assessing leaf N status of apple (Neilsen et al., 1995a, 1995b; Park et al., 2007; Porro et al., 2001), grapevine (Porro et al., 2001), and grapefruit (Li et al., 1998). It is easy, rapid, and non-destructive. However, the correlation between the SPAD readings and N concentrations varied depending on growth stages of the tree (Neilsen et al., 1995b; Park et al., 2007) and environmental conditions (Neilsen et al., 1995b; Porro et al., 2001). Less is known for persimmon trees, although the readings were reported to be related to leaf N concentration (Choi et al., 2008). If SPAD readings are highly related to leaf N concentration of persimmon throughout the season, a standard curve could be developed. A SPAD meter would then be highly useful in estimating leaf N status to quickly determine whether N should be additionally applied at that time.
Many persimmon orchards are equipped with fertigation facilities in Korea. Combining fertigation with the chlorophyll meter could be extremely useful in managing N nutrition of the trees, thereby minimizing surplus N in the orchards. This experiment was conducted 1) to determine the changes in leaf SPAD readings and N concentrations as affected by different N fertigation rates; 2) to find the relationship between the two variables throughout the season; and 3) to provide seasonal SPAD readings obtained from some well-managed orchards producing premium-grade fruits.
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