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Abstract

Forcing azalea (Rhododendron sp. cvs. Redwing, Mission Bells and Gloria were subjected to sufficient and low levels of N, K, and Ca, and the difference in concentration of these nutrients was measured and termed “differential”. Immature, recently mature, and old leaves were sampled periodically from current shoots during development. Ca differential was not related to sample position. N differential was exhibited in a similar manner but was best expressed in older leaf tissue during late growth. The magnitude of the K differential was related to both sample position and sample date; the largest expression occurred in young leaf tissue during early growth and on older leaf tissue during late shoot development. The best single sample position for foliar analysis of these nutrients was the most recently mature leaves on current shoots.

Salinity guidelines for seed germination substrates call for low, difficult to attain levels. This study was conducted to determine the value of N, P, K, and S as preplant nutrients, with the anticipation that some could be eliminated to alleviate the high salinity problem in many substrates. Impatiens wallerana L. `Accent Rose' and Gomphrena globosa L. `Buddy' were tested in 288-cell plug trays containing a substrate of 3 sphagnum peat moss: 1 perlite (v/v) in two experiments. Seven preplant N, P, K, and S treatments, including none, all (each at 100 mg·L^-1 of substrate), all minus one of each of the nutrients, and N at one additional rate of 50 mg·L^-1, were tested. Postplant fertilization was applied to all treatments as 13 N-0.9P-10.8K at 50 mg·L^-1 N beginning 1 week after sowing and was increased to 100 mg·L^-1 N when the fourth true leaf appeared. The resultant seedlings were transplanted into 48-cell flats and grown into marketable stage for further evaluation. For maximum potential growth, N, P, K, and S were needed as preplant fertilizer. However, compact shoots, not maximum growth, are generally desired in commercial production. Thus, K and S can be omitted since their contribution to growth was only occasional and small. To further ensure a consistently desirable level of compactness, it was necessary to omit N or P or both in addition to K and S. Omission of N alone yielded the most desirable compact plant qualities, including suitable reduction in final seedling size. Omission of P alone yielded larger reductions in height and shoot dry weight of seedlings compared to N omission, and a delay of 2 to 4 days in flowering of bedding plants. Omission of the four nutrients, compared to -P, resulted in similar seedling growth reduction and bedding plant flower delay. Since N omission lowered the salt (electrical conductivity) level of substrate more than P omission and had no negative impact on subsequent bedding plant flowering compared to the other two treatments, N omission would be the more desirable of the three. However, N omission resulted in chlorotic seedlings, but these quickly turned green upon restoration of N. Omission of P or all four nutrients resulted in desirably deep green seedlings. Growth of gomphrena seedlings, a high-fertilizer requirement category of taxa, was suppressed when the preplant rate of N was 50 mg·L^-1 compared to 100 mg·L^-1, while growth of impatiens, a low-fertilizer requirement category of taxa, was essentially equivalent at these rates. Preplant additions of nutrients applied at 100 mg of nutrient element per liter of substrate lasted for the following numbers of days; NO₃-N, 18-25 days; NH₄-N, 12-20 days; K₂O, 27 days; PO₄-P, >35 days; and SO₄-S, >35 days.

The effect of CO₂ concentration (330 and 675 μL·L⁻¹) and photosynthetic photon flux (PPF) (mean daily peaks of 550–1400 μmol·m⁻²·s⁻¹) on total mineral contents in shoots was studied in chrysanthemum [Dendranthema ×grandiflorum (Ramat) Kitam ‘Fiesta’] during three times of the year. Growth (as measured by shoot dry weight) and shoot mineral contents (weight of nutrient per shoot) of hydroponically grown plants were analyzed after 5 weeks. There was a positive synergistic interaction of CO₂ concentration and PPF on growth with the greatest growth at high PPF (1400 μmol·m⁻²·s⁻¹) with high CO₂ (675 μL·L⁻¹). When growth was not used as a covariate in the statistical model, both CO₂ concentration and PPF significantly affected the content of all eight nutrients. However, after growth was included as a covariate in the model, nutrients were classified into three categories based on whether CO₂ concentration and PPF level were needed in addition to growth to predict shoot nutrient content. Neither CO₂ concentration nor PPF level was needed for Mg, Fe, and Mn contents, whereas PPF level was needed for N, P, K, and Ca contents, and both CO₂ concentration and PPF level were required for B content.