Morphology and foliar chemistry of containerized Abies fraseri (Pursh) Poir. seedlings as affected by water availability and nutrition

• We present the results of a two-year (2007–2008) greenhouse study investigating the effect of water availability and nitrogen fertilization on the growth, biomass partitioning, and foliar nutrient content of Abies fraseri (Pursh) Poir. • Fertilizer and moisture content (irrigation) were varied in a factorial experiment combining four levels of irrigation and three levels of fertilization to evaluate growth and foliar nutrient content. In addition, a numerical optimization was used to estimate appropriate levels of each factor necessary to achieve simulated goals for response variables. • Irrigation increased the height growth by 12 to 35% depending on the fertilization treatment (p = 0.0001). Fertilization increased height growth by 10 to 26% (p = 0.02). A similar response was observed for stem diameter growth (SDG). Total biomass accumulation increased as result of positive response of stem and root biomass development, and foliar nitrogen content was positively affected by nitrogen fertilization and negatively affected by irrigation. The numerical optimization for simulated target growth and nitrogen content responses produced levels of input combinations with high desirability factors to achieve the target responses. • These results suggest that nutrient addition is a strong determining factor for early development of this species. The improved growth efficiency in this study is likely attributed to a combination of factors including, improved photosynthetic capacity, decreased stomatal limitations, or increased resource allocation to stems

Gibberellic acid inhibitors control height growth and cone production in <i>Abies fraseri</i>

<p>Precocious cone production in Fraser fir (<i>Abies fraseri</i>) results in substantial economic losses for Christmas tree growers in the United States. Cone removal often represents the second highest labor expense, after shearing. Gibberellins (GAs) regulate both reproductive development and shoot elongation, and are used to enhance cone production in conifer seed orchards. We identified plant growth regulators (PGRs) that inhibit GA biosynthesis – paclobutrazol, applied by foliar spray (PBZ-foliar) or soil injection (PBZ-soil), and chlormequat. We evaluated the effects of PGR treatments on cone production and vegetative growth in three tree size classes (small, medium, and large) at four locations over a three-year period. PGRs were applied in spring 2013, but did not affect growth until 2014, nor did they affect cone production until 2015. In 2014, PBZ reduced leader length by 21–29% across size classes and sites, while also increasing bud density by 11–20%. In 2015, PBZ-soil reduced average cone density (cones/tree) in small, medium, and large trees by 33%, 54%, and 40%, respectively. PBZ-soil also reduced leader length by 20–29% and increased bud density by 16–25%, making it the most effective PGR at controlling height growth and cone production in Fraser fir.</p

A Review of Chemical Weed Control Practices in Christmas Tree Production in the United States

Christmas trees are sensitive to weed competition, especially during establishment. In initial stages of the tree crop, weeds can utilize available soil moisture and trees may succumb to drought stress. In later stages, weeds can even interfere with production practices. Non-chemical weed control methods alone may not provide effective weed control. Chemical weed management strategies involve the use of preemergence and postemergence herbicides at the right timing and application rates. There are many herbicides that are used in Christmas tree production in the United States, and each has specific application guidelines and weed control spectra. Moreover, crop trees vary in tolerance by species and tree age. Growers need to be careful while applying herbicides as many of these chemicals can cause injury to Christmas trees. Repeated application of herbicides with the same mechanism of action has resulted in development of herbicide resistance among several weed species. Managing herbicide resistance has now become an important issue. More research is required on identifying and managing herbicide resistance among weed species in Christmas tree production. Future research needs to focus on herbicide and mulch combinations, herbicide rotations, and tank mixing different herbicides with different mechanisms of actions and how these affect Christmas tree varieties

Effect of substrate compost percentage on green roof vegetable production

Use of rooftops to produce locally grown vegetables is increasing. However, due to weight restrictions, shallow substrate depths, and potential harsh environmental conditions, optimizing production can be a challenge. Standard industry practices for ornamental extensive green roofs planted with succulents or other herbaceous perennials and grasses dictate that organic matter should be less than 20% of the original substrate mix. In rooftop agriculture, however, maximizing growth and yields are usually a primary objective and the amount of organic matter incorporated into these substrates are a major factor in this equation. In this study we quantified the optimal percentage of compost in a green roof substrate for optimizing growth and yields for cucumbers (Cucumis sativus) and peppers (Capsicum annuum). The study was conducted on raised green roof platforms over a period of 19 weeks and compared six substrates containing increasing amounts of a commercial compost produced from municipal yard waste (0, 20, 40, 60, 80, and 100%) mixed with a heat-expanded shale and sand base. These treatments were also compared to a typical garden plot at ground level. Plant performance evaluations such as plant growth, chlorophyll fluorescence (Fv/Fm) as an indicator of plant stress, and fruit yields were used as an indicator for optimal substrate mixtures. Generally, the addition of 60 or 80% compost resulted in the greatest plant growth and fruit yields, although compost influenced growth and yield of peppers to a greater degree than cucumbers. In addition, the ground garden plots performed poorly which emphasizes the point that growing vegetables on a rooftop can be advantage because substrates can be engineered to maximize plant health, although the same could be done with raised beds in a garden plot. (C) 2015 Elsevier GmbH. All rights reserved

Water Conserving Irrigation Practices, Plant Growth, Seasonal Crop Coefficients, and Nutrition of Container-Grown Woody Ornamentals

Irrigation practices for container nursery crops often result in over-application and can lead to leaching of nutrients and reduced growth. Our objectives were to: (1) compare growth and foliar nutrient content for plants under daily water use (DWU) based irrigation treatments, (2) determine DWU of 14 woody ornamental taxa, and (3) classify taxa into irrigation functional groups based on crop coefficients (KC). Irrigation was applied daily to 8 taxa in 2009 and 2010 using a control of 19 mm and three irrigation treatments: (1) replacing 100% plant DWU (100DWU) each day, (2) alternating 100% DWU with 75% DWU in a 2-day cycle (100-75DWU), and (3) a 3-day cycle replacing 100% DWU the first day and 75% DWU on the second and third days (100-75-75DWU). In 2009, seasonal average DWU ranged between 8.8 and 17.3 mm depending on taxa and treatment. Most DWU-based treatments resulted in less water applied than the control, yet plant growth was not reduced, and for one taxon (Hydrangea paniculata &lsquo;Limelight&rsquo;) the 100DWU increased plant growth index. Lower foliar P and K concentrations were found for several taxa in control versus DWU treatments. In 2010, DWU for the season ranged between 2.1- and 22.0-mm d&minus;1 depending on taxa and treatment. Growth was lower only for 100-75-75DWU Hydrangea paniculata &lsquo;Limelight&rsquo; compared to other treatments and there were no differences in foliar nutrient content

Robust Model Predicts Shoot Phenology of Fraser Fir under Extreme Conditions

Fraser fir (Abies fraseri [Pursh] Poir.) is an important Christmas tree species in the United States, and understanding its phenology is important for managing Fraser fir trees in plantations or forests. Many management decisions are informed by and dependent on shoot phenology, from late spring frost protection to shearing, and from timing pesticide sprays to managing cone production. The ability to predict important phenological stages will become increasingly important as the climate warms, as is predicted for the primary regions where Fraser fir is grown for Christmas trees. Here, we report on the development of a model of shoot phenology in Fraser fir, and present one example of how this model may be applied to the problem of managing cone production. We surveyed shoot phenology at nine Christmas tree plantations in Michigan over three years, and used the data obtained to develop a phenology model of shoot growth. Derived from the beta sigmoid function and based on growing degree days, this phenology model offers a high predictive power and is robust to extremes of temperature and precipitation. When applied to cone production, our model provides guidance for timing practices that influence cone bud formation, both for reducing nuisance cones in Christmas tree plantations and for enhancing cone production in seed orchards. In addition, the model may assist with timing other practices tied to shoot phenology. The performance of our model under extreme heat and drought conditions suggests a role for this and other phenology models in predicting and mitigating the effects of climate change on tree growth and development