With recent advances in N analyzers, the Dumas method becomes more attractive as a replacement for Kjeldahl N. Kjeldahl N (K_N):Dumas N (D_N) ratios were determined for anthurium (A), orchid (O), fern (F) and turf (T). Dry tissues were ground to pass a 20-mesh seive. D_N was determined using 0.2 g of sample and a Leco FP-428. K_N was determined by digesting 0.4 g tissue with a CuO/TiO/K 2 SO 4 catalyst and 10 mL H 2 SO 4 at 450°C for 2 hr. Ammonium in the digest was assayed by colorimetry (Lachat analyzer). Overall (n=397 obs.), D_N was a good estimator of K_N: K_N = 0.90 (p<0.01) D_N + 0.09 (p=0.03) , R 2 =0.93, over the 0.4-6.6 N range. K_N:D_N ratio was significantly (p<0.01) affected by plant type. Ratios of 0.85 for A, 0.92 for T, 0.99 for O, and 1.00 for F may be used to estimate K-N from D-N for the diagnosis of N nutrition, along with existing interpretative data.
`Freedom' poinsettias ( Euphorbia pulcherrima Willd. ex Kl.) were grown to flowering in solution culture for 11 weeks. Treatments consisted of five ammonium: nitrate nitrogen ratios: 1:0, 3:1, 1:1, 1:3, and 0:1 with a total N concentration of 150 mg N/liter. The balance of essential nutrients was supplied with a modified Hoagland's solution. Fresh weight, dry weight, and macro- and micronutrient content of bracts, leaves, petioles, stems, and roots were determined at the end of the study. Leaf and bract area also was measured. Maximum bract size was achieved with 100% nitrate (0:1) treatment. Leaves were largest with the 1:3 ratio. Plants receiving ammonium as the sole N source exhibited severe ammonium toxicity symptoms: stunted growth, foliar chlorosis and necrosis, premature leaf abscission, stunted and clubby roots, and delayed or nonexistent bract coloring. Dry weights for bracts, leaves, stems, and roots increased as the ratio of nitrate increased. Elemental uptake was monitored weekly. Nitrogen-form effect on the uptake, concentration, and partitioning of other nutrients also was evaluated.
Abstract With recent advances in nitrogen (N) analyzers, the Dumas method may replace the Kjeldahl method for the routine diagnosis of N in plants. Since these two methods recover different N fractions and no conversion factor is available to convert Dumas N (Dn) to Kjeldahl N (Kn) data, Kn:Dn ratios were determined for selected ornamentals (anthurium, Anthurium andraeanum Linden; orchid spp. Cattleya, Dendrobium, Oncidium, Phalaenopsis, and Vanda; leatherleaf fern, Rumohra adiantiformis (G. Forst) Ching; tree fern, Asparagus densiflorus (Kunth) Jessop) and turfgrasses (creeping bentgrass, Agrostis palustris Huds. cv. Penncross; bermudagrass, Cynodon dactylon L.). Samples were dried at 70°C for 72 hr and ground to pass a 20‐mesh sieve. Kn was determined by colorimetry after digestion of 0.4 g of tissue using a CuSO4/TiO/K2SO4 catalyst and 10 mL of H2SO4 at 450°C for 2 hr. Dn was determined using 0.2 g of sample and a LECO FP‐428 N Analyzer. Over the 0.4–6.6% N range, Dn was a good predictor of Kn; Kn = 0.90 Dn + 0.09 (R2=0.93, p‐model<0.01, n=397 obs.). The Kn: Dn ratio was significantly (p<0.01) affected by plant type (Kn: Dn = 0.85, 0.92, 0.99, and 1.00 for anthurium, turfgrasses, orchid and fern, respectively). The more practical way to use the ratios in routine interpretation was to adjust existing sufficiency ranges with the inverse of these ratios. Adjusted sufficiency ranges (in %N) were 4.9–6.6 for creeping bentgrass, 2.4–4.4 for bermudagrass, and 1.9–3.6 for anthurium. Existing sufficiency ranges for orchid and fern need not be adjusted for Dumas N.
Nutritional levels of mature vs. young leaves of Anthurium (Anthurium andraeanum Linden.) cultivars were determined over a seven year period. Nutritional levels for essential nutrients tested (B, Ca ++ , Cu ++ , Fe ++ , K + , Mg ++ , Mn ++ , Mo - , P, and Zn ++ ) were determined with inductively coupled plasma emission spectrometry. Kjeldahl N was determined with a flow injection analyzer. The young leaf, 90% mature, was determined to be the most accurate predictor of the nutritional status of anthuriums. These values were established for the cultivars `Kozohara', `Nitta Orange', `Kaumana', and `Ozaki'.
