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  • Author or Editor: Andrew G. Ristvey x
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The influence of fertilization rate on nitrogen (N) and phosphorus (P) nutrient partitioning and uptake efficiency of young, container-grown azalea (Rhododendron L. ‘Karen’) was determined under controlled greenhouse conditions during Spring 2001 and 2002. In 2001, fertilizer treatments included a factorial combination of two N (25 or 250 mg/week) and three P (0, 5, or 25 mg/week) rates; in 2002, an additional N rate (100 mg/week) was included in the experimental design. Five destructive harvests were performed during each study; plant tissues (root, stem, primary and secondary branches and leaves) from each harvest were analyzed to derive total N and P uptake. Leachates from containers were monitored and analyzed weekly to calculate nitrate (NO3-N), ammonium (NH4-N), and orthophosphate (PO4-P) loss. Fertilization rates of 5 mg P per week in 2001 and rates of 100 mg N per week and 5 mg P per week in 2002 maintained optimal growth compared with the highest fertilization rates (250 mg N and 25 mg P per week) in these studies. Increasing N fertilization rate largely promoted shoot growth, whereas decreasing N and P fertilization rates promoted root growth and increased uptake efficiency. In general, increasing N and P fertilization rates increased nutrient N and P leaching from the pine bark substrate. Reducing excess N and P fertilization to match plant growth requirements of young azalea increases nutrient uptake efficiency and reduces nutrient loss to the environment.

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Many agronomic and horticultural studies on nutrient uptake and use-efficiency have indicated, in general, that agricultural crops are poor competitors for nitrogen (N) and phosphorus (P) in soil-based systems, with estimates of overall nutrient efficiency being less than 50% for N and 10% for P. Low efficiencies are due to losses from leaching, runoff, gaseous emissions and soil fixation, but uptake efficiency is also affected by rate and timing (i.e. seasonal effects) of applications. Controlled-release fertilizers (CRF's) have been promoted as a technology that can slowly release nutrients; the release rate is most often a function of prill coating and temperature. There are few data in the ornamental literature that have directly compared the total uptake efficiency of CRF's to soluble fertilizer sources. From 1999-2002, we collected three annual N and P budgetary datasets, comparing two species (Rhododendron cv. azalea and Ilex cornuta cv.`China Girl') with different growth rates and hence nutrient requirements. Plant N and P uptake efficiencies were usually less than 20% of the total applied, but all datasets included a significant soluble fertilization component. In 2003, a new study with Ilex cornuta cv.`China Girl' was initiated, where nutrients were supplied only from two CRF sources, as we want to determine whether this technology can significantly increase nutrient uptake efficiency at similar rates. A preliminary analysis of the data indicate that total N and P uptake efficiencies between different CRF sources were similar, but leaching losses between sources varied during the growing season. It appears that the primary determinant of uptake efficiency is not source material or timing, but the overall rate of nutrient application.

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The genus Aronia Medik., also known as chokeberry, is a group of deciduous shrubs in the Rosaceae family, subtribe Malinae. The two commonly accepted black-fruited Aronia species are black chokeberry [Aronia melanocarpa (Michx.) Elliott] and aroniaberry [Aronia mitschurinii (A.K. Skvortsov & Maitul)]. The geographic range of wild A. melanocarpa is the Great Lakes region and the northeastern United States, with a southerly extension into the higher elevations of the Appalachian Mountains. Wild A. melanocarpa found in New England are diploids, whereas plants throughout the rest of the range are tetraploids. A. mitschurinii is a cultivated hybrid between ×Sorbaronia fallax (C.K.Schneid.) C.K.Schneid. and A. melanocarpa and exists as a tetraploid. There is currently limited diversity of Aronia genotypes in the ornamental and fruit industries, and many of the current cultivars are not adapted to the southern United States and similar environs with limited chilling to break winter dormancy. The goal of this study was to determine 1) the chilling requirements for A. mitschurinii ‘Viking’ and 2) the range of chilling requirements for wild A. melanocarpa genotypes from different geographic origins. Two experiments were conducted in which plants were subjected to various chilling accumulation treatments and then moved to a greenhouse for observation of budbreak and subsequent growth. Expt. 1 was conducted at the University of Maryland at Wye, MD, and focused solely on the commercial cultivar A. mitschurinii ‘Viking’. Outdoor, ambient fall and winter temperatures were used to achieve the chilling treatments. In Expt. 1, we determined the optimal chilling requirements for A. mitschurinii ‘Viking’ to be greater than 900 h using the single temperature model. Expt. 2 was conducted at the University of Connecticut and focused on wild genotypes, plus A. mitschurinii ‘Viking’. A fixed temperature cold room was used to achieve chilling treatments. In Expt. 2, we found A. melanocarpa genotypes from southern regions in the United States required chilling accumulation of 600 h (single temperature model), compared with genotypes from northern regions that required more than 900 h of chilling accumulation. Tetraploid A. melanocarpa required 900 h of chilling to break bud, but diploid A. melanocarpa required 1200 h of chilling to break bud. Expt. 2 confirmed the 900-h chilling requirement for A. mitschurinii ‘Viking’. For both experiments, the rate of budbreak and shoot growth was positively correlated with increasing amounts of chilling.

Open Access

Phedimus kamtschaticus (Fischer) were grown in three experimental crushed brick-based green roof substrates (GRSs) with increasing organic matter (OM) content (10%, 20%, and 40% by volume) and a commercially available blend, Rooflite®, in single-pot replicates in a growth chamber for 6 months. Three unplanted replicates of each substrate were included in the design and received identical irrigation volumes as planted replicates. Three destructive harvests indicated that increased substrate OM increased plant root and shoot biomass; however, plants grown in Rooflite® demonstrated greater succulence in the second and third destructive harvests despite similar substrate OM content. By the end of the growth study, there was no difference in dry weight accumulation between the Rooflite® and 40% OM treatment despite the difference in succulence between the two treatments. Substrate volumetric water content (VWC) ranged from 22.5% to below 5% during three consecutive periods of imposed water stress with no differences in evapotranspiration (ET), indicating plants were accessing substrate water previously assumed to be unavailable. Cumulative water loss (normalized for plant dry weight) indicated a likely shift into crassulacean acid metabolism (CAM) around 60-hour postirrigation. Planted treatments (n = 6) lost more water cumulatively (P < 0.05) compared with the unplanted controls (n = 3), although there were no differences in total water loss between substrate treatments.

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Quantifying the range of fertilizer and irrigation application rates applied by the ornamental nursery and greenhouse industry is challenging as a result of the variety of species, production systems, and cultural management techniques that are used. To gain a better understanding of nutrient and water use by the ornamental industry in Maryland, 491 potential operations (including multiple addresses and contacts) in the state were mailed a packet of information asking for their voluntary participation. Of the 491 potential operations, it was determined that 348 operations were currently in operation. Of those 348 operations, 48 (14% of the operations in the state) participated in a site visit and an in-depth interview, and a detailed site analysis of the water and nutrient management practices was performed on a production management unit (MU) basis. The authors define an MU as a group of plants that is managed similarly, particularly in regard to nutrient and irrigation application. Greenhouse operations reported, on average, 198, 122, and 196 kg/ha/year of nitrogen (N), phosphorus (P, as P2O5), and potassium (K, as K2O) fertilizer used, respectively, for 27 operations, representing 188 MUs. Twenty-seven outdoor container nursery operations had a total of 162 MUs, with an average of 964, 390, and 556 kg/ha/year of N, P2O5, and K2O fertilizer used, respectively. Field nursery (soil-based) operations were represented by 17 operations, producing 96 MUs, with an average of 67, 20, and 25 kg/ha/year of N, P2O5, and K2O fertilizer used, respectively. Irrigation volume per application was greatest in container nursery operations, followed by greenhouse and field nursery operations. Data were also analyzed by creating quartiles, which represent the median of the lowest 25%, the middle 50%, and highest 75% of values. It is likely that the greatest quartile application rates reported by growers could be substantially reduced with little to no effect on plant production time or quality. These data also provide baseline information to determine changes in fertilization practices over time. They were also used as inputs for water and nutrient management models developed as part of this study. These data may also be useful for informing nutrient application rates used in the Chesapeake Bay nutrient modeling process.

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Increasing environmental concerns and legislation in many states and in other countries require that we take a more comprehensive sustainable “best management” approach to production techniques in nursery and greenhouse operations. This is particularly important because these production facilities are typically intense users of resources that are applied to relatively small land areas. We have developed an online knowledge center to facilitate the implementation of more sustainable practices within the nursery and greenhouse industry. A web-based knowledge center provides the most cost-effective mechanism for information delivery, as our potential audiences are extremely diverse and widespread. We currently have a registered user database of over 450 educators, growers, and industry professionals, and undergraduate and graduate students. A gateway website provides an overview of the issues and the goals of the project. The associated knowledge center currently has 25 in-depth learning modules, designed in a Moodle learning management framework. These learning modules are designed to actively engage learners in topics on substrate, irrigation, surface water, and nutrient and crop health management, which are integral to formulating farm-specific strategies for more sustainable water and nutrient management practices. Additional modules provide assessment and implementation tools for irrigation audits, irrigation methods and technologies, and water and nutrient management planning. The instructional design of the learning modules was paramount because there can be multiple strategies to improve site-specific production practices, which often require an integration of knowledge from engineering, plant science, and plant pathology disciplines. The assessment and review of current practices, and the decision to change a practice, are often not linear, nor simple. All modules were designed with this process in mind, and include numerous resources [pictures, diagrams, case studies, and assessment tools (e.g., spreadsheets and example calculations)] to enable the learner to fully understand all of the options available and to think critically about his/her decisions. Sixteen of the modules were used to teach an intensive 400-level “Principles of Water and Nutrient Management” course at the University of Maryland during Spring 2008 and 2009. The water and nutrient management planning module also supports the nursery and greenhouse Farmer Training Certification program in Maryland. The Maryland Department of Agriculture provides continuing education credits for all consultants and growers who register and complete any module in the knowledge center. Although these learning resources were developed by faculty in the eastern region of the United States, much of the information is applicable to more widespread audiences.

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