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The USDA/ARS National Small Grains Collection currently contains more than 40,000 accessions of common and durum wheats, and about 6000 accessions of other Triticum species. The Wheat Crop Advisory Committee has discussed the use of core subsets in screening this vast collection for traits of interest in breeding. The collection curator is assembling a subset, stratified by geography and morphology, for distribution in response to nonspecific requests and diversity evaluation. However, we have concluded that no subset(s) can be identified, in advance, that would be useful in screening for parental germplasm with traits of interest to breeding programs. Resistances and other traits are often rare in the collection, but the initial subset used for screening can be enriched for the trait of interest by selecting accessions based on knowledge of environmental conditions or occurrence of pests in geographic regions. New database technology will be very useful in this effort.

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Abstract

Root exudation patterns and carbohydrate composition of roots and leaves of Citrus jambhiri Lush, were examined during the period of initial colonization by Glomus fasciculatum (Thaxt.) Gerd. and Trappe. Exudation of reducing sugars and amino acids from seedling roots decreased as soil and root P increased. Comparison of vesicular-arbuscular mycorrhizal (VAM) seedlings to nonmycorrhizal seedlings of similar size and P nutrition revealed root exudation in VAM plants decreased following fungal colonization. Root reducing sugars increased and root starch content decreased in VAM seedlings during the infection process. Following establishment of symbiosis, leaves of VAM seedlings had greater levels of total soluble sugar, sucrose, reducing sugars, and starch relative to nonmycorrhizal controls. Colonization of C. jambhiri roots by VAM fungi apparently alters the balance of carbohydrates within leaves and roots.

Open Access

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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Abstract

Glasshouse-grown seedlings of white oak (Quercus alba L.) received foliar applications of 3 concentrations of 6-benzylamino-purine (BA), 3 of gibberellic acid (GA), and 2 concentrations of an NPK solution (750 and 1500 ppm). The 1500 ppm NPK treatment significantly stimulated seedling dry weight when applied in combination with 50 ppm BA or GA, with BA producing the greater treatment effect. Application of 50 ppm BA or GA also stimulated significant increases in seedling root system length, root collar diameter, and total leaf area. The results suggest that foliar mist applications of plant growth regulators in combination with foliar fertilizer solutions promote oak seedling root and shoot growth.

Open Access

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 State of Maryland Legislature enacted the Water Quality Improvement Act in 1998, which requires all agricultural operations to develop and implement nitrogen- and phosphorus-based nutrient management plans by December 2002. This legislation also mandates the education and training of professionals who will write nutrient management plans, and growers who will implement them. Maryland Cooperative Extension faculty have therefore been charged with developing effective educational programs that will enable nursery and greenhouse industry professionals to achieve these goals and ensure industry compliance with this legislation.

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A nutrient delivery system that may have applicability for growing plants in microgravity is described. The Vacuum-Operated Nutrient Delivery System (VONDS) draws nutrient solution across roots that are under a partial vacuum at ≈91 kPa. Bean (Phaseolus vulgaris L. cv. Blue Lake 274) plants grown on the VONDS had consistently greater leaf area and higher root, stem, leaf, and pod dry weights than plants grown under nonvacuum control conditions. This study demonstrates the potential applicability of the VONDS for growing plants in microgravity for space biology experimentation and/or crop production.

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A cooperative project between the Univ. of Florida Cooperative Extension Service, USDA Natural Resources Conservation Service, and Consolidated Farm Services Agency to address farm nutrient use and water management in the Lake Apopka hydrologic unit area of Florida began in 1991. This area was selected due to the vegetable production on the organic soils (muck) and sandy soils north of Lake Apopka, Florida's most polluted large lake. Discharge of nutrient-laden water into the lake from the 4050-ha vegetable production area has been implicated as a major contribution to the hypereutrophic status of the lake. Changes in cultural practices including water management, which would lead to a reduction in nutrient loading, should aid in the restoration of the lake. A grower survey of fertilizer application rates was conducted each year for 4 years with the baseline established by the 1991 survey. Demonstration plots using soil tests as the basis for fertilizer rates compared to normal grower rates of fertilizer were established for carrots, sweet corn, and celery. In 1995, muck growers had reduced their total application of N by 16%, P 52%, and K 32%, without reducing yields or quality. Nutrient applications were reduced by over 656 t/year over the years surveyed. Farms have saved fertilizer and reduced environmental risks.

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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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