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Kirsten Rasmussen Starkey and Asger Roer Pedersen

Experiments were performed on miniature potted roses (Rosa) to investigate whether increasing the Ca concentration in the nutrient solution would increase the Ca concentration in the rose plant, resulting in better postharvest quality. The plants were watered during the whole production period with six different nutrient solutions with Ca at 1.1 to 4.4 mm and varying meq ratios between Ca and the cations. During the postharvest period, plant characteristics were recorded at days 0, 11, 14, 18, and 25. Increasing Ca in the nutrient solution significantly increased the Ca concentration of the plants. However, the NH4 level (2% to 5% vs. 22% to 25%) also influenced the Ca concentration of the plants. Leaves had the highest Ca concentration, which was more than twice the level in flowers and buds, stems and roots. There were no differences in dry matter content between treatments in roots or tops at marketing stage. At the start of the postharvest treatment (day 0), plants from the highest Ca treatment had significantly fewer flowers than those in all of the other treatments due to delayed development. The number of good flowers increased from days 0 to 14 irrespective of treatment, while a further increase to day 18 was observed in plants from the three highest Ca treatments (low NH4) due to a negative effect on flower longevity of low Ca and high NH4 in the three low-Ca treatments. By day 25, the number of good flowers had decreased markedly in all treatments, but plants from the second-highest Ca treatment had significantly more good flowers than plants from the other treatments. Flower wilting was due to infection by grey mold (Botrytis cinerea) and a physiological condition that caused wilting that began at the petal edges with a dark discoloration. Infection with grey mold was negatively correlated with Ca concentration in the flowers. The physiological wilting was seen earlier in plants from the treatments with high NH4 and is probably not related to Ca concentration in the flowers.

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Catherine S.M. Ku and David R. Hershey

Single-pinched poinsettias (Euphorbia pulcherrima Willd. ex Klotzsch `V-14 Glory') received 210 mg·L-1 constant N fertigation from Hoagland solution with N sources of 100% NO3-N or 60% NO3-N : 40% NH4-N, P concentrations of 7.8 or 23 mg·L-1, and leaching fractions (LFs) of 0, 0.2, or 0.4. The P fertigation rates did not significantly affect plant growth measurements and N leaching. Shoot dry masses and leaf and bract areas of plants fertigated with 60% NO3-N were 11% to 26% greater than those fertigated with 100% NO3-N. Shoot dry mass at the 0 LF was 27% smaller than those at the 0.4 LF. The total amount of N applied via fertigation was 1.7 g at the 0 LF and 3.3 g at the 0.4 LF. Leachate N concentration ranged from 170 to 850 mg·L-1. Nitrogen recovery was 74% to 91%, and the percentage of fertigation N recovered in leachate ranged from 51% at the 0.2 LF to 74% at the 0.4 LF. With a 0.4 LF and 210 mg·L-1 N fertigation, 15% to 22% of the recovered N was found in the shoots, and 68% to 75% was found in the leachate. Even with a 0.2 LF, >50% of the N recovered was found in the leachate. Premium marketable quality poinsettia were produced with N at 210 mg·L-1 from 60% NO3-N : 40% NH4-N fertigation solution at the 0.4 LF. To reduce N leaching to the environment, good marketable quality poinsettias could be grown at a LF of ≤0.2 with 210 mg·L-1 N fertigation if quality irrigation water is available and if a small reduction in growth is acceptable.

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Jeff Taylor, Eric Simonne, and John Murphy

Because cucumber mosaic virus (CMV) affects southernpea (Vigna unguiculata) grown in the southeast, plants were preconditioned with different nutrient solutions from germination to the flowering stage, 24 DAT (days after transplanting) and rub inoculated with CMV. Symptoms were observed at a rate of 1/5, 1/5, 4/5, and 4/5 (observed infected plants/plants infected) in the Al, NH4, NO3, and Na treatments, respectively. At 67 DAT, ELISA detected CMV at a rate of 5/5, 5/5, 4/5, and 4/5 (detected infection/plants infected) of the Al, NH4, NO3, and Na treatments, respectively. The interaction of inoculation and preconditioning was nonsignificant for fresh or dry weight (P > 0.10); however, nutritional preconditioning significantly (P < 0.01) affected the fresh and dry weight. These preliminary data suggest that nutritional preconditioning affects southernpea plants' reaction to CMV.

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F.J.A. Niederholzer and S.A. Weinbaum

The relationship between nitrogen (N) status and N uptake capacity has not been assessed in fruit trees. Determination of root uptake capacity by depletion of unlabeled N from external solution is less costly than methods using 15N, but is reportedly not suited for excised root studies due to reductions in uptake rates with time (Pearcy, R.W. et al. (eds). 1989. Plant Physiological Ecology, p. 195. Chapman and Hall. New York.). We tested two hypotheses: I) excised peach root NH4+ uptake rates are constant over several hours exposure to NH4+ solution and 2) excised peach root NH4+ uptake rates are negatively correlated with tree N status. Mature, N deficient, field grown `O'Henry' trees on `Lovell' peach (Prunus persica L. Batch.) rootstocks and growing in Winters, CA received (NH4)2SO4 at a rate of 200 kg N/ha on September 29, 1993. An equal number of control trees received no N fertilizer. Foliar N deficiency symptoms of fertilized trees disappeared within 3 weeks of fertilization. On Nov. 9, 1993 (prior to leaf fall), excised roots were obtained from two fertilized and two unfertilized trees. Root NH4+ accumulation rates per unit root dry weight or root length were constant over 5 hours of exposure to 70 μM NH4+ (initial concentration) for both fertilized and unfertilized trees. Unfertilized tree root NH4+ uptake rates were significantly greater than those of fertilized trees on a root dry weight or length basis. Excised root NH4+ uptake may prove to be a sensitive index of fruit tree N status.

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Leah E. Willis, Frederick S. Davies, and D.A. Graetz

One-year-old `Hamlin' orange [Citrus sinensis (L.) Osb.] trees on sour orange rootstock (C. aurantium L.) were used to compare various fertigation frequencies and rates with application of granular materials. In Expt. 1, granular fertilizer was applied five times per year or liquid fertilizer was applied five, 10, or 30 times per year at 0.23 kg N/tree per year as an 8N-3.4P-6.6K formulation. In Expt. 2, an additional treatment of granular and liquid material was applied three times per year, but fertilizer rate and formulation were the same as in Expt. 1. Experiment 3 included the same application frequencies as Expt. 1, but with two rates of N (0.11 or 0.06 kg N/tree per year). Soil samples were taken from each treatment 1, 4, and 7 days after fertilization at depths of 0-15, 16-46, and 47-76 cm for nutrient analyses. Trunk diameter, shoot growth, and tree height were similar for all treatments 8 months after planting in Expts. 1 and 2, while trees in Expt. 3 had significantly less growth at the lower rate. Soil NH4-N and NO3-N concentrations for all liquid treatments within 1 week of fertilization were highest for the five times per year treatment at the 0- to 15-cm depth, but nutrient concentrations of all liquid treatments were similar at the other depths. For most dates and depths, NH4-N and NO3-N concentrations were similar for both fertilizer rates.

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K.S. Reddy and H.A. Mills

Responses of two hydroponically grown marigold species, Tagetes erects L. `pumpkin Crush' and T. patula L. `Janie Yellow', to Mn concentrations of 0.5 mg·liter-1 or 10 mg·liter-1 with KNO3 and Ca(NO3)2 (NO3 source) or NH4N O3 as the N source were investigated. In both species, Mn uptake was enhanced with the NO3 source while reduced with NH4NO3. With Mn supplied at 0.5 mg·liter-1 and NO3 as the N source, T. erects absorbed twice the Mn per gram of dry matter as T. patula. T. erecta accumulated higher concentration of Mn in the shoot than in the root irrespective of the N source. T. patula accumulated higher concentration of Mn in the roots with the NO3 source while NH4NO3 shifted the Mn accumulation to the shoot. Growth of both species was suppressed with 10 mg Mn/liter and the suppression was greater with the NO3 source than with the NH4NO3. These results indicate an interspecific response to Mn concentration as well as an N source influence on the uptake of Mn in marigold grown under hydroponic conditions.

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J.R. Heckman, W.T. Hlubik, D.J. Prostak, and J.W. Paterson

Research was conducted with sweet corn (Zea mays L.) to evaluate the presidedress soil NO3 test (PSNT) originally developed for use on field corn on a wide range of New Jersey soils. Soil NO3-N concentrations reflected differences in N availability due to manure or preplant N application. The relationship between soil NO3-N concentration and relative yield of marketable ears was examined using Cate–Nelson analysis to define the PSNT critical level. Soil NO3-N concentrations >25 mg·kg–1 were associated with relative yields at ≥92%. The success rate for the PSNT critical level was 85% for predicting whether sidedress N was needed. Including NH4-N in the soil analysis did not improve the accuracy of the soil test for predicting whether sidedress N was needed. Although the PSNT is quite accurate in identifying N-sufficient sites, it appears to offer only limited guidance in making N-fertilizer rate predictions. The PSNT is most useful on manured soils, which frequently have sufficient N. The test likely will help decrease the practice of applying “insurance” fertilizer N and the ensuing potential for NO3 pollution of the environment.

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Helen T. Kraus, Stuart L. Warren, and Charles E. Anderson

Five ratios of NH4+: NO3-(100:0, 75:25, 50:50, 25:75, and 0:100) were evaluated for impact on growth of Cotoneaster dammeri Schneid. `Skogholm' (cotoneaster), a woody ornamental shrub, and Rudbeckia fulgida Ait. `Goldsturm' (rudbeckia), an herbaceous perennial. Nitrate alone decreased dry weight and leaf area of cotoneaster and rudbeckia compared with mixtures of NH4+ and NO3- and NH4+ alone. Additionally, NO3- alone suppressed accumulation of cationic nutrients and N in cotoneaster, while mixes of NH4+ and NO3- enhanced accumulation of nutrients in roots and shoots of rudbeckia compared with solutions containing either NH4+ or NO3- alone. The steles of roots of cotoneaster and rudbeckia contained more secondary xylem with larger tracheary elements with a mix of 25 NH4+: 75 NO3- than with NO3- alone.

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Paulette B. Craig and Janet C. Cole

Spiraea japonica L. f. `Froebelii' were grown in 3.8-L containers filled with substrates consisting of recycled paper (RP) and pine bark at rates of 0%, 25%, 50%, 75%, or 100% (by volume) RP. Fertilizer treatments included 100% of the recommended rate of N as controlled release (CRF) or liquid fertilizer (LF) or both. The same amounts of N (as NO3 --N and NH4 +-N), P and K were supplied with each fertilizer treatment. Plants were irrigated in Fall 1996 based on substrate water-holding capacity and to achieve a 25% to 50% leaching fraction. In Spring 1997 regardless of substrate water holding capacity, plants were irrigated weekly initially, then twice weekly later in the study when plants were larger. Fertilizer treatment did not affect plant size, but plant diameter and shoot and root dry weight decreased as substrate RP concentration increased in Fall 1996. All plant size parameters measured decreased as substrate RP concentration increased regardless of fertilizer treatment in Spring 1997. In Fall 1996, shoot and root N concentration increased as CRF decreased (and LF increased), but substrate RP concentration did not affect shoot or root N concentration. In Spring 1997, shoot and root N concentration generally decreased as substrate RP concentration increased with 50% CRF, 50% LF, or 100% LF. Leachate NO3 --N, NH4 +-N and total N generally increased as CRF decreased but decreased as substrate RP concentration increased in both years. Substrate volume and percentage of air space decreased, but bulk density increased, as RP concentration increased. Although N leaching decreased as substrate RP concentration increased in both years, reasonable plant growth occurred only in those substrates containing ≤50% RP.

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Peter M. Bierman, Carl J. Rosen, and Harold F. Wilkins

Poinsettia (Euphorbia pulcherrima Wind. ex. Klotzsch cv. Gutbier V-14 Glory) plants were grown under conditions simulating commercial stock plant production to investigate the effects of NH4-N: NO3-N fertilizer ratios, foliar Ca sprays, medium-applied Ca, and medium-applied Mo on leaf edge burn (LEB) and cutting production. Leaf edge burn expression was nearly 100% greater with NH4-N: NO3-N fertilizer ratios of 1:2 or 2:1 than with NO3-N only. However, cutting production was 28% lower with NO3-N as the sole N source. There was little difference in either LEB or cutting production between the two NH4-N levels. Weekly Ca sprays at 500 mg·liter-1 were effective in reducing LEB, while medium-applied Ca as gypsum was ineffective. Foliar Ca sprays reduced both the number of LEB leaves (90%) and symptom severity of individual leaves. Spraying plants with tap water (Ca at 25 to 30 mg·liter-1) plus wetting agent had an intermediate effect. Medium-applied Mo was ineffective in reducing LEB, despite greatly increasing leaf Mo levels. The Ca concentration in chlorotic, marginal leaf tissue was significantly lower than the Ca concentration in green leaf margins. There was also a strong, negative correlation between the Ca concentration in young leaves at the susceptible growth stage and the incidence of LEB in various treatment groups. Supplemental applications of Ca and Mo did not consistently affect cutting production. Leaf edge burn appears to be a localized Ca deficiency due to inadequate Ca uptake and/or translocation to the numerous axillary shoots simultaneously developing on poinsettia stock plants.