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Mary Ann Rose

Timing nutrient application to periods of high nutrient demand could increase nutrient use efficiency and reduce the potential for fertilizer leaching or runoff. However, current recommendations for field nursery and landscape ornamentals (extension publications) suggest fertilizing in late fall and early spring despite research with perennial fruit crops that demonstrates low uptake potential during those times. Research is needed to resolve this apparent conflict. Application rates for woody ornamentals, established in the 1960s and 1970s, also need reexamination in the light of environmental concerns.

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Mary Ann Rose and Mark A. Rose

A closed-loop photosynthesis system and a heat-balance sap-flow gauge independently confirmed oscillatory transpiration in a greenhouse-grown Rosa hybrids L. Repetitive sampling revealed 60-minute synchronized oscillations in CO2-exchange rate, stomatal conductance, and whole-plant sap-flow rate. To avoid confusing cyclical plant responses with random noise in measurement, we suggest that gas-exchange protocols begin with frequent, repetitive measurements to determine whether transpiration is stable or oscillating. Single measurements of individual plants would be justified only when transpiration is steady state.

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Mary Ann Rose, Mark Rose and Hao Wang

Crabapple [Malus ×zumi (Rehd.) `Calocarpa'] and maple (Acer ×freemanii E. Murray `Jeffersred') trees were grown in containers from 22 June to 3 Oct. with three fertilizer concentrations (50, 100, and 200 mg·L-1 N) and two levels of moisture tension in the medium [low setpoint (moist) = 5 kPa and high setpoint (dry) = 18 kPa]. Whole-plant growth was enhanced more by minimizing water stress than by increasing fertilizer concentration. Shoot length and whole-plant dry weight were greater (>29% for crabapple and >90% for maple) in low tension treatments (low water stress) but were unaffected by fertilizer concentration. Moisture tension also had a dominant effect on dry-weight allocation to leaves, stems, and roots. In contrast, foliar nutrient concentrations increased with fertilizer concentration but were affected to a lesser degree by moisture tension. Seasonal patterns in biomass allocation were little affected by treatments; the largest proportions of leaf and root biomass accumulated during summer and fall, respectively.

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Mary Ann Rose, Mark Rose and Hao Wang

Fertilizer recommendations for woody ornamentals suggest applying nutrients in early spring at budbreak, and in fall at the time of leaf coloration or leaf abscission. Because plants lack functional leaves at those times, there would be minimal contributions from photosynthesis to active ion absorption or from transpiration to mass flow of ions in soil towards roots. Thus, we hypothesized that fertilizer efficiency also would be low at those times. To estimate N uptake efficiency, 15N-enriched fertilizer was applied to container linden trees at one of five times during the 1998 season: at budbreak, during active growth, after terminal bud-set, before leaf abscission, and during leaf abscission. Half of the plants received 15N-nitrate-enriched ammonium nitrate on each date, and half received 15N-ammonium-enriched ammonium nitrate. Treated plants were harvested 10 days after enriched fertilizer application (29 May, 6 July, 17 Aug., 28 Sept., and 16 Nov.). Patterns of uptake were not different between plants treated with 15N-ammonium- or 15N-nitrate-enriched fertilizer. In both cases, nitrogen recovery efficiencies at budbreak and leaf abscission were much lower than at other application times. Whole-plant recovery efficiency of 15N-nitrate-enriched ammonium nitrate was 10% at budbreak, 13% at leaf abscission, and ranged from 58% to 71% for the intervening times. Recovery of 15N-ammonium-enriched ammonium nitrate was 6% at budbreak, 24% at leaf abscission, and 42% to 56% for intervening times.

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Mary Ann Rose and Barbara Biernacka

Seasonal patterns of N, P, and K accumulation and remobilization in Freeman maple (Acer× freemanii E. Murr. `Jeffersred') were studied to guide future improvements in fertilization efficiency. Leaves, stems, and roots of container-grown trees were harvested over a 12-month period (June to June) in each of two experiments. Plants were fertilized from June to October with three rates of soluble fertilizer (50, 100, and 200 mg·L-1 N). Fertilizer rate had linear and quadratic effects on dry weight and nutrient contents, but did not affect seasonal accumulation patterns. Whole-plant nutrient contents and dry weights increased until mid-October, prior to leaf abscission. The largest fractions of nutrients and dry weight were allocated to leaves until early September. Between September and October, the most rapid accumulation of N, P, and dry weight occurred in root tissue. Highest nitrogen recovery efficiency occurred in late summer (Expt. 2) or early fall (Expt. 1). There was no statistically significant evidence for N, P, or K resorption in the fall, but evidence of N (not of P or K) remobilization in the spring was very strong. Whole plant dry weight doubled between April and June, while ≈50% of the N stored in woody tissues was translocated to new shoots.

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Barbara Biernacka and Mary Ann Rose

Seasonal patterns of N uptake and allocation in Buxus microphylla, Acer × freemanii and Fothergilla gardenii were investigated for improving fertilization strategies. Rooted cuttings were planted to 3.5-L containers 25 May 1995. Plants were drip-irrigated on an as-needed basis with N at 50, 100, or 200 mg·L–1 solutions. Leaves, stems, and roots were destructively harvested every 6 weeks, starting 24 June. Net changes in dry weight and N uptake were determined for each of four, 6-week periods. Increasing N rate increased tissue N concentration in all species, and reduced root: shoot ratios in Acer and Fothergilla. Dry weights of Acer increased with N rate; whereas other species gave no positive response in dry weight beyond N at 100 mg·L–1. Nitrogen at the 200-mg·L–1 rate caused severe injury to Fothergilla. Nitrogen uptake of the deciduous species increased in the first three periods, with greatest N uptake between 1 Sept. and 12 Oct. Greatest N uptake in Buxus occurred between 15 July and 1 Sept. Total N content in Buxus increased between 15 Oct. an 1 Dec. with a large proportion of N appearing to shift from leaf to stem tissue. In the other species, leaf abscission caused a net reduction in total N contents in the 100 and 200 mg·L–1 rates, although stem and root N contents increased. Increasing N rate in Acer delayed fall coloration but hastened leaf abscission. End-of-season N recovery (N taken up/N applied) was extremely low, and decreased with increasing rate of N. Acer had the highest recoveries (4.1%, 2.6%, and 2.0%) for low, medium, and high fertilizer rates, followed by Buxus (2.6%, 2.2%, 1.0%) and Fothergilla (1.7%, 1.8%, 0.4%).

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Hao Wang and Mary Ann Rose

Nutrient uptake and allocation patterns of Forsythia ovata × europaea `Meadowlark' grown in a recirculating hydroponic system in the greenhouse were observed for 5 months. Dormant rooted cuttings were placed in the system on 8 May 1995. The nutrient solution supplied (in mg·L–1) 100 N, 48 P, 210 K, 30 Mg, 60 Ca, 117 SO4, 3 Fe, 0.5 Mn, 0.15 Zn, 0.15 Cu, 0.5 B, 0.1 Mo. Solutions were completely replaced every 2 weeks. Leaves, stems, and roots were harvested for dry weight and nutrient analysis at monthly intervals. Nitrogen uptake and dry-weight accumulation in the roots increased throughout the experiment, reaching a maximum in the fifth month (September). Nitrogen uptake and dry-weight accumulation of leaves and stems increased rapidly throughout the first 3 months, then leveled off. Whole-plant N recovery (N taken up/N in hydroponics system) reached a maximum (58%) between 6 July and 3 August. N recovery in the hydroponics system was about 10 times greater than what we observed in related experiments with woody plants in typical production environments, suggesting that there is potential for manipulating fertilization and cultural practices to increase fertilization efficiency in woody ornamentals. Nutrient recovery and accumulation patterns of P and K also will be presented.

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Mary Ann Rose and Hao Wang

Micronutrient supplements were applied to container rhododendron (Rhododendron L. × `Girards Scarlet' [Girard Evergreen Hybrid Group]) in three forms: uncoated micronutrient fertilizer; slow-release, NPK-plus-minors fertilizer; and biosolids compost (15% v/v). Control plants received no supplement. While all micronutrient treatments had significantly higher foliar Mn or Cu concentrations than controls 1 year after potting, they did not increase growth (dry weight) or plant quality. At 1, 3, and 12 months after potting, the compost treatment had significantly higher diethylenetriaminepentaacetic acid (DTPA)-extractable levels of Mn, Fe, and Zn in the medium. Only one micronutrient fertilizer treatment increased extractable micronutrient concentrations (Cu) on all testing dates. Correlations between medium-extractable and foliar micronutrient concentrations were low (r 2 < 0.30). Vigorous growth in the control treatment suggested that adequate levels of micronutrients were supplied by the pine bark-hardwood bark-peat-sand medium. September concentrations [ppm (mg·L-1)] as low as 2.0 Mn, 17.8 Fe, 0.3 Cu, 4.2 Zn, and 0.9 B in DTPA extracts produced acceptable growth in rhododendron through the following June.

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Mary Ann Rose and Larry J. Kuhns

Large bare-root liners of Gleditsia triacanthos `Moraine' and Pyrus calleryana `Aristocrat' were planted in spring, 1989. Five trees of each species were pruned by removing 50% of the length of each shoot at planting; 5 control trees were not pruned. After 4 months the trees were harvested and the following measurements were taken on the season's new growth increment: total number of elongated shoots and unelongated shoots (< 1 cm in length), total and average length of elongated new shoots, stem and leaf dry weights.

Growth responses of the 2 species to treatments were nearly identical. Pruned trees had fewer shoots than controls but a much higher proportion of elongated to unelongated shoots. This could be the result of a release of apical dominance. The average new shoot length of pruned trees was 2-3 times that of controls, and the total new shoot length was significantly greater. New stem dry weights of the pruned trees were also greater than the controls, but leaf dry weights were not significantly different. Total shoot weights (stems plus leaves) were not different. In this study there was no difference between treatments in the total seasonal growth increment as measured by weight. An equivalent amount of new growth was distributed on fewer, but more rapidly-elongating branches in the pruned trees.

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Mary Ann Rose and Larry J. Kuhns

Large bare-root liners of Gleditsia triacanthos `Moraine' and Pyrus calleryana `Aristocrat' were planted in spring, 1989. Five trees of each species were pruned by removing 50% of the length of each shoot at planting; 5 control trees were not pruned. After 4 months the trees were harvested and the following measurements were taken on the season's new growth increment: total number of elongated shoots and unelongated shoots (< 1 cm in length), total and average length of elongated new shoots, stem and leaf dry weights.

Growth responses of the 2 species to treatments were nearly identical. Pruned trees had fewer shoots than controls but a much higher proportion of elongated to unelongated shoots. This could be the result of a release of apical dominance. The average new shoot length of pruned trees was 2-3 times that of controls, and the total new shoot length was significantly greater. New stem dry weights of the pruned trees were also greater than the controls, but leaf dry weights were not significantly different. Total shoot weights (stems plus leaves) were not different. In this study there was no difference between treatments in the total seasonal growth increment as measured by weight. An equivalent amount of new growth was distributed on fewer, but more rapidly-elongating branches in the pruned trees.