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Raul I. Cabrera and Diana Devereaux

Ilex opaca and Lagerstroemia indica plants were grown over 9 months using complete nutrient solutions differing in N concentration [(N)A: 15, 30, 60, 120, 210 and 300 mg·L–1]. Biomass production increased as (N)A were raised from 15 to 60 mg·L–1, but was depressed by higher concentrations. Increases in (N)A produced higher shoot: root ratios. Maximum leaf N concentration was observed at 60 mg·L–1, with similar values at higher (N)A. Plant survival, establishment and performance was evaluated over 15 weeks following transplant (15 WAT) to a landscape with minimum management conditions. Despite the initial significant differences in growth, shoot: root ratios and plant N status, plant establishment was not affected following transplant. Plant characteristics changed significantly over time, and by 15 WAT, all of the measured variables were statistically the same across all treatments. Flowering was, however, delayed over several weeks for Lagerstroemia indica plants grown at the higher (N)A. Analysis of these results indicate that plant production under relatively low N levels in the nursery maximizes N fertilizer use efficiency without affecting landscape establishment and performance.

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Peter R. Hicklenton and Kenneth G. Cairns

Containerized Cotoneaster dammeri `Coral Beauty' and Forsythia `Northern Gold' were grown in a 2 bark: 1 peat: 1 sand (by volume) medium containing 5 kg·m–3 Nutricote 16N–4.4P–8.1K, Type 140, under four irrigation regimes: drip (DR; 20 min/day; two periods), overhead (OV; 90 min/day; two periods), overhead pulse (OP; 28 min/day; four periods), and subirrigation (SU). Volumes of 0.33, 0.35, and 0.14 liters·day–1 were delivered to each container in the DR, OV, and OP systems, respectively. SU was supplied from a geotextile-covered sand bed. End-of-season dry weights of Cotoneaster and Forsythia were 41% and 55% greater, respectively, in SU-grown plants compared to their OV-irrigated counterparts. Differences in growth between the other three regimes were minor for both species. Pre-dawn and dusk water potentials did not differ between plants in the four regimes, but midday potentials were slightly lower in SU- and DI-irrigated plants. End-of-season foliar N and P content differed only slightly between irrigation treatments, but K levels were significantly higher in SU plants. The reasons for better growth under SU remain obscure but may be related to improved medium nutrient retention and improved fertilizer use efficiency under an irrigation regime in which water moves upwards from the pot base to top.

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N.F. Gariglio, R.A. Pilatti and B.L. Baldi

In Santa Fe, Argentina, strawberries (Fragari ×ananassa Duch.) are cultivated in the area of Coronda where N fertilization usually exceeds crop requirements. The objective of this work was to test four types of fertilization methodology to optimize fertilizer use efficiency. Experiments were carried out at the horticultural center of the Facultad de Agronomía y Veterinaria, in Esperanza, Santa Fe, 31.15° S latitude, on a typical argiudol soil. `Chandler' was planted 13 Mar. 1996. Nitrogen demand was related to the dry matter production with N content decreasing to increment of biomass (W), soil N mineralization was estimated according to the program EDAFO version 3. Using previous data, a monthly balance was calculated and four treatments were devised: control (T0) = without fertilization; treatment 1 (T1) = N fertilization covering the accumulated monthly deficit, 53 kg·ha-1 (47 lb/acre); treatment 2 (T2) = N fertilization covering the monthly deficit 66 kg·ha-1 (58 lb/acre); treatment 3 (T3) = N fertilization covering the total crop demand 117 kg·ha-1 (104 lb/acre). All N treatments significantly increased yields over the control. Yield increased to increasing N rates from 0 to 53 kg·ha-1. This response was due to an increase in fruit number but not in fruit weight. High N rates promoted runner growth without increasing fruit yield. The use N balance method for strawberry fertilization showed satisfactory results. Accumulated N balance (T1), required the least amount of N fertilizer while producing good yield, thus it should be the method adopted to reduce costs and environmental risks of N fertilization.

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K.T. Morgan, J.M.S. Scholberg, T.A. Obreza and T.A. Wheaton

Growth and nitrogen (N) accumulation relationships based on tree size, rather than age, may provide more generic information that could be used to improve sweet orange [Citrus sinensis (L.) Osbeck] N management. The objectives of this study were to determine how orange trees accumulate and distribute biomass and N as they grow, investigate yearly biomass and N changes in mature orange trees, determine rootstock effect on biomass and N distribution, and to develop simple mathematical models describing these relationships. Eighteen orange trees with canopy volumes ranging between 2 and 43 m3 were dissected into leaf, twig, branch, and root components, and the dry weight and N concentration of each were measured. The N content of each tree part was calculated, and biomass and N distribution throughout each tree were determined. The total dry biomass of large (mature) trees averaged 94 kg and contained 0.79 kg N. Biomass allocation was 13% in leaves, 7% in twigs, 50% in branches/trunk, and 30% in roots. N allocation was 38% in leaves, 8% in twigs, 27% in branches/trunk, and 27% in roots. For the smallest tree, above-/below-ground distribution ratios for biomass and N were 60/40 and 75/25, respectively. All tree components accumulated biomass and N linearly as tree size increased, with the above-ground portion accumulating biomass about 2.5 times faster than the below-ground portion due mostly to branch growth. The growth models developed are currently being integrated in a decision support system for improving fertilizer use efficiency for orange trees, which will provide growers with a management tool to improve long-term N use efficiency in orange orchards.

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Ted E. Bilderback

Environmentally compatible production practices are conscious efforts to design and retrofit nursery container growing areas to improve irrigation and nutrient efficiency, and reduce exposure of ground and surface water supplies to contaminated effluent. Irrigation of ornamental crops in containers can be very inefficient, using large quantities of water and fertilizer. Irrigation water and fertilizer use efficiencies are directly related to each other. Improving irrigation efficiency improves nutrient efficiency and reduces water volume and nutrients leaving production beds. Increasing efficiency can be accomplished in many ways. Grouping plant species and container sizes into blocks with similar water requirements improves efficiency. Redesigning overhead sprinkler systems to accomplish uniform distribution across growing beds or replacing worn nozzle orifices can significantly reduce application variability. Low volume/low pressure systems that distribute water directly into containers and apply less water in a specific amount of time compared to overhead sprinkler application, will conserve water. Applying irrigation in short cycles rather than long cycles improves wetting in substrates and conserves electrical energy, water and directly reduces nutrient leaching from containers. Creating microclimates in nurseries to optimize light or reduce container temperatures, disease pressure and crop stress can improve water and nutrient efficacy. Flow of water running off growing areas must be engineered to slow velocity, filter and contain effluent. Strategies should be site-specific. Capture, containment and recycling of irrigation water has been a common practice in many nurseries in the U.S., as a means to provide adequate water supplies. Vegetative filter strips adjacent to beds and containment basins have been installed at nurseries to reduce contaminants in runoff before water enters recycle irrigation supplies. In areas with sandy soils, some nurseries have developed closed systems where drainage channels and collection basins are lined to prevent nitrogen movement from runoff into shallow groundwater.

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J.M.S. Scholberg, L.R. Parsons and T.A. Wheaton

Improving our understanding of processes that control and limit nitrogen uptake by citrus can provide a scientific basis for enhancing nitrogen fertilizer use efficiency. Nitrogen uptake dynamics of two rootstock seedlings will be compared to those of young budded trees. Three-month old Swingle citrumelo [Citrus paradisi Macf. × Poncirus trifoliata (L.) Raf.] and Volkamer lemon (C. volkameriana Ten. & Pasq.) trees were planted in PVC columns filled with a Candler fine sand. Field experiments were conducted using 4-year-old `Hamlin' orange trees [Citrus sinensis (L.) Osb.] grafted on `Carrizo' [C. sinensis × Poncirus trifoliata (L.) Raf.] or on Swingle citrumelo. Trees were either grown in solution culture using 120-L PVC containers or in 900-L PVC tubs filled with a Candler fine sand. Additional trees were planted in the field during Spring 1998. Two lateral roots per tree were trained to grow in slanted, partly burried, 20-L PVC columns filled with a Candler fine sand. Nitrogen uptake from the soil was determined by comparing the residual N extracted by intensive leaching from planted units with that of non-planted (reference) units. With the application of dilute N solutions (7 mg N/L), plants reduced N concentrations to near-zero N concentrations within days. Applying N at higher concentrations (70 or 210 mg N/L) resulted in higher initial uptake rates, increased residual soil N levels, and reduced nitrogen uptake efficiency. Contributions of passive uptake to total nitrogen uptake ranged from less than 5% at soil solution concentrations around 3 ppm N to 20% to 30% at concentrations of 60 ppm N.

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Jeffrey G. Williamson and E. Paul Miller

Bearing `Misty' and `Star' southern highbush blueberries were grown on pine bark beds and fertilized at three rates using granular and liquid fertilizers with a 3–1–2 (1N–0.83K–0.88P) ratio. Granular fertilizer was applied 8 times per year at 4-week intervals beginning in April and continuing through October. Liquid fertilizer was applied with low volume irrigation 16 times per year at 2-week intervals during the same period. During the growing season, irrigation was applied at 2- to 3-day intervals in the absence of rain. A 2 cultivar × 2 fertilizer type × 3 fertilizer rate factorial arrangement of treatments was replicated 8 times in a randomized complete-block design. All fruits were harvested from single-plant plots at 3- to 4-day intervals. Canopy volume was not affected by fertilizer type, but fruit yield was slightly greater for granular than for liquid fertilizer treatments. In 2003, fruit yield of 2.5-year-old `Misty' and `Star' plants increased with increasing fertilizer rates up to the highest rate tested (50 g N/plant/year). Similarly, in 2004, fruit yields increased with increasing fertilizer rates up to the highest rate (81 g N/plant/year). Root distribution was limited to the 12-cm-deep layer of pine bark with very few roots penetrating into the underlying soil. The positive growth responses of blueberry plants to high fertilizer rates in pine bark beds suggests that soluble fertilizer was leached through the pine bark layer into the soil below the root zone. More frequent, lighter applications of soluble fertilizers, use of slow-release or controlled-release fertilizers, and careful irrigation management may improve fertilizer use efficiency of blueberry plantings on pine bark beds.

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Daphne L. Richards and David Wm. Reed

New Guinea impatiens (Impatiens hawkeri Bull.) `Illusion' were grown in a recirculating subirrigation system under various rates and placements of 14N-6.1P-11.6K (Osmocote; Scotts-Sierra, Marysville, Ohio) resin-coated, controlled-release fertilizer (CRF). Four CRF placements (incorporated, top-dressed, bottom, and dibble) were tested. Incorporated placement yielded slightly greater dry weights than the other placements. A rate experiment tested incorporating from 0.5 to 2 times the fertilizer manufacturer's recommended rate of 7.11 kg·m-3. All shoot growth parameters (height, leaf number, shoot, and root fresh and dry weight) exhibited a significant quadratic response, as exemplified by shoot dry weight, where shoot dry weight increased up to the 1.5× rate, after which shoot dry weight decreased. A quadratic response surface model revealed that the optimum rate response ranged from 1.16× rate for height to 1.47× rate for shoot dry weight. The lower bound of the 95% confidence interval (CI) would be the lowest rate at which one could expect maximum growth response. The lower bound of the 95% CI varied from 0.56× rate for height to 1.30× rate for shoot dry weight. Thus, the lowest rate that would be within the 95% CI for all growth parameters, and thus yield maximum growth response, would be the 1.30× rate. Electrical conductivity (EC) of the growing media increased significantly with increasing CRF rate. At all rates, EC was significantly greater in the top layer than in the middle and bottom layers. Only in the 1.75× and 2× rates did EC exceed the recommended EC levels in the middle and bottom layer. All rates >0.75× exceeded recommended EC in the top layer. Release characteristics and total nutrient balance of the CRF was compared in subirrigated and top-watered systems. There was no significant difference between top-watered and subirrigated treatments for the amount of K recovered in plant tops and released from prills. By day 84, in subirrigation, 46% of the K was still in the prills, 41% was recovered in the plant tops, and 22% was recovered in the medium. Similar results were obtained in the top-watering treatment, except that a lesser amount was recovered in the medium (9%) and a small amount (4%) was recovered in the leachate. The uptake of K by plants and release of K by the CRF were inversely proportional and linear with respect to time. Of the K released from the prills, 77% and 83% were recovered in the plant tops for subirrigation and top-watering, respectively, indicating very high fertilizer use efficiency.

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Dan TerAvest, Jeffrey L. Smith, Lynne Carpenter-Boggs, Lori Hoagland, David Granatstein and John P. Reganold

is nitrogen (N) supply because organic fertilizers are often bulky and expensive, and release of N can be slow and unpredictable. Improving the understanding of N cycling in organic systems and increasing organic fertilizer-use efficiency are critical

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Silvia Jiménez, Mónica Pérez, Blanca María Plaza, Roberto Salinas and María Teresa Lao

use of the nutrients and greater water and fertilizer use efficiency ( Jiménez and Lao, 2005 ). Some models for the estimation P uptake have been developed. The general models that study the P dynamic in the soil, including plant uptake, are ANIMO