Brian E. Jackson

Advancements in Root Growth Measurement Technologies and Observation Capabilities for Container-Grown Plants

The study, characterization, observation, and quantification of plant root growth and root systems (Rhizometrics) has been and remains an important area of research in all disciplines of plant science. In the horticultural industry, a large portion of the crops grown annually are grown in pot culture. Root growth is a critical component in overall plant performance during production in containers, and therefore it is important to understand the factors that influence and/or possible enhance it. Quantifying root growth has varied over the last several decades with each method of quantification changing in its reliability of measurement and variation among the results. Methods such as root drawings, pin boards, rhizotrons, and minirhizotrons initiated the aptitude to measure roots with field crops, and have been expanded to container-grown plants. However, many of the published research methods are monotonous and time-consuming. More recently, computer programs have increased in use as technology advances and measuring characteristics of root growth becomes easier. These programs are instrumental in analyzing various root growth characteristics, from root diameter and length of individual roots to branching angle and topological depth of the root architecture. This review delves into the expanding technologies involved with expertly measuring root growth of plants in containers, and the advantages and disadvantages that remain.

Chemical Properties of Biochar Materials Manufactured from Agricultural Products Common to the Southeast United States

The use of biochar as a soil amendment has fostered much attention in recent years due to its potential of improving the chemical, physical, and biological properties of agricultural soils and/or soilless substrates. The objective of this study was to evaluate the chemical properties of feedstocks, common in the southeast United States, and their resulting biochar products (after being torrefied) and determine if the chemical properties were within suitable ranges for growers to use the biochar products as root substrate components. Poultry litter biochar produced at 400 C for 2 hours had a higher total phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), chloride (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), sodium (Na), and zinc (Zn) concentration than biochar made using the same process withmixed hardwood species, miscanthus (Miscanthus capensis), cotton (Gossypium hirsutum) gin trash, switchgrass (Panicum virgatum), rice (Oryza sativa) hull, and pine (Pinus sp.) shavings feedstocks. The pH of the biochar products ranged from 4.6 for pine shaving biochar to 9.3 for miscanthus biochar. The electrical conductivity (EC) ranged from 0.1 dS m for mixed hardwood biochar to 30.3 dS m for poultry litter biochar. The cation exchange capacity (CEC) of the biochar products ranged from a low of 0.09meq/g for mixed hardwood biochar to a high of 19.0 meq/g for poultry litter biochar. The waterextractable nitrate, P, K, Ca, Mg, sulfate, boron, Cl, Cu, Fe, Mo, Na, and Zn were higher in poultry litter biochar than in all of the other types of biochar. The high EC and mineral element concentration of the poultry litter biochar would prevent its use in root substrates except in very small amounts. In addition, the high degree of variability in chemical properties among all of the biochar products would require users to know the specific properties of any biochar product they used in a soil or soilless substrate. Modifications to traditional limestone additions and fertility programs may also need to be tested and monitored to compensate for the biochar pH and mineral nutrient availability. Users should be aware that biochar products made from different feedstocks can have very different chemical properties even if the same process was used to manufacture them.

Growth Response of Herbaceous Ornamentals to Phosphorus Fertilization

A series of experiments investigated the effects of increasing phosphate– phosphorus (P) concentrations on the growth and development of four horticultural species. In experiment 1, petunia [Petunia atkinsiana (Sweet) D. Don ex W.H. Baxter] plants were grown using eight P concentrations, and we found that the upper bound for plant growth was at 8.72–9.08mg·L P, whereas concentrations £2.5 mg·L P caused P deficiency symptoms. Experiment 2 investigated P growth response in two cultivars each of New Guinea impatiens (Impatiens hawkeri W. Bull) and vinca [Catharanthus roseus (L.) G. Don]. Growth for these plants was maximized with 6.43–12.42 mg·L P. In experiment 3, ornamental peppers (Capsicum annuum L. ‘Tango Red’) were given an initial concentration of P for 6 weeks and then switched to 0mg·L P to observe whether plants could be supplied with sufficient levels of P, and finished without P to keep them compact. Plants switched to restricted P began developing P deficiency symptoms within 3 weeks; however, restricting P successfully limited plant growth. These experiments indicated that current P fertilization regimens exceed the P requirements of these bedding plants, and depending on species, concentrations of 5–15 mg·L P maximize growth. Producers of floriculture crops strive to cultivate compact and healthy plants that are considered high quality and attractive for consumers. The fertilization regimen has a significant role in the ultimate appearance and robustness of a crop. Many commercial fertilizers mixed at recommended concentrations for greenhouse production supply greater phosphorus (P) concentrations than required by plants, as is the case with 20 nitrogen (N)– 8.7P–16.6 potassium (K). This fertilizermixed at a concentration of 200 mg·L N would provide 87 mg·L P. One recommendation for greenhouse crops by McMahon (2011) suggests using concentrations of only 5–10 mg·L P. Other studies have indicated that P concentrations of just 0.093–1.5 mg·L can keep floriculture crops healthy yet compact (Borch et al., 1998; Hansen and Nielsen, 2000, 2001). This disparity among P recommendations and P concentrations supplied in common fertilizers brings into question what level of P is required to produce healthy floriculture crops. Recent research investigated the minimum P concentrations required by herbaceous ornamentals (Borch et al., 1998; Hansen and Nielsen, 2000, 2001; Nelson et al., 2012). These studies were focused on the potential of using low P fertilization to control plant growth. Although the nitrate (NO3 ) form of N has often been used to keep plants compact, it is the low P levels in high NO3 –N fertilizers that are responsible for compactness (Nelson et al., 2012). Most NO3 – based fertilizers recommended for compact plant growth are also low in P. Erroneously, it was thought that fertilizer formulations high in ammoniacal nitrogen (NH4 ) result in greater plant growth. Experiments conducted by Nelson et al. (2002) used constant ratios of N source, but varied P concentrations, and found that plant size increased with increasing P concentrations. Previously, it was thought that higher P concentrations would only increase growth until plant P concentration reached 0.25% of total dry matter (Nelson et al., 2002). Potential issues with very low P fertilization result from the fact that the soilless substrates used in floriculture production have limited P holding capacity (Marconi and Nelson, 1984). Without adequate P, crops have the potential to deplete the initial P concentration in the substrate and may begin reallocating P from older plant tissues, leading to the development of deficiency symptoms on the lower leaves (Mengel et al., 2001). Deficiency symptoms associated with P are commonly observed when dry plant tissue comprises <0.2% or 2000 mg·kg P (Mills and Jones, 1996). Typical symptoms are often described as a reddening or purpling of the lower foliage, an overall darker green coloration, stunted growth, delayed flowering, and greater root lengths (Epstein and Bloom, 2005; Marschner, 1995; Mengel et al., 2001). For leaf tissue concentrations, a range of 0.2% to 0.5% of total plant dry weight is considered sufficient P for most plants (Mills and Jones, 1996). This study aimed to determine the P concentration required by several floriculture species to optimize growth. Determining optimal P concentrations will provide improved grower recommendations and limit commercial fertilizer waste. Materials and Methods Experiment 1. Two cultivars of petunia [Petunia atkinsiana (Sweet) D. Don ex W.H. Baxter ‘Surprise Sky Blue’ and ‘Potunia Neon’] cuttings (D€ummen Orange, Columbus, OH) were planted on 28 Sept. 2015 in 128 cell plug trays with cell dimensions of 2.7 · 2.7 · 3.8 cm (length · width · depth) and rooted under mist without fertilization. Plants were propagated and grown in a glassglazed greenhouse at North Carolina State University, Raleigh, NC (35 N latitude) under natural photoperiod. Greenhouse day/night temperature set points were 23.9/18.3 C, and the average daily temperature (ADT) was 19.7 C. The substrate used for all aspects of the experiment was an 80:20 (v:v) mix of Canadian sphagnum peatmoss (Conrad Fafard, Agawam, MA) and horticultural coarse perlite (Perlite Vermiculite Packaging Industries, Inc., North Bloomfield, OH), amended with dolomitic limestone at 8.875 kg·m (Rockydale Agricultural, Roanoke, VA) and wetting agent (AquaGro 2000 G; Aquatrols, Cherry Hill, NJ) at 600.3 g·m. This custom substrate was used to ensure that there was no initial P concentration. Twenty-eight-day old rooted cuttings were transplanted into 12.7 cm diameter (855 mL) pots (Dillen, Middlefield, OH). Concentrations of 0, 1.25, 2.5, 5, 10, 20, 40, and 80 mg·L P were used to determine the upper and lower bounds of growth response to P. The experiment was completely randomized with eight single-plant replications of eight treatments. Fertilization began at transplant, and fertilizers were custom blends of the following individual technical grade salts: calcium nitrate tetrahydrate [Ca(NO3)2·4H2O], potassium nitrate (KNO3), monopotassium phosphate (KH2PO4), potassium sulfate (K2SO4), magnesium sulfate heptahydrate (MgSO4·7H2O), magnesium nitrate [Mg(NO3)2], iron chelate (FeDTPA), manganese chloride tetrahydrate (MnCl2·4H2O), zinc chloride heptahydrate (ZnCl2·7H2O), copper chloride dihydrate (CuCl2·2H2O), boric acid (H3BO3), and sodium molybdate dihydrate (Na2MoO4·2H2O). Phosphorus (referring to phosphate-phosphorus) concentrations were varied among treatments whereas other essential nutrients were adjusted to remain as constant as possible. NO3 – N and K were held at 150 mg·L, with all other essential microelements remaining constant (Henry, 2017). Received for publication 21 June 2017. Accepted for publication 21 Aug. 2017. We are grateful for the funding support provided by the Fred C. Gloeckner Foundation, the USDA Floriculture and Nursery Research Initiative, American Floral Endowment Altman Family Scholarship, and The Garden Club of America. We would also like to express our gratitude to D€ummen Orange for providing cuttings and for peat moss provided by Sun Gro Horticulture. Corresponding author. E-mail: josh.brady.henry@

Maximum Plant Uptakes for Water, Nutrients, and Oxygen Are Not Always Met by Irrigation Rate and Distribution in Water-based Cultivation Systems

Growing on rooting media other than soils in situ -i.e., substrate-based growing- allows for higher yields than soil-based growing as transport rates of water, nutrients, and oxygen in substrate surpass those in soil. Possibly water-based growing allows for even higher yields as transport rates of water and nutrients in water surpass those in substrate, even though the transport of oxygen may be more complex. Transport rates can only limit growth when they are below a rate corresponding to maximum plant uptake. Our first objective was to compare Chrysanthemum growth performance for three water-based growing systems with different irrigation. We compared; multi-point irrigation into a pond (DeepFlow); one-point irrigation resulting in a thin film of running water (NutrientFlow) and multi-point irrigation as droplets through air (Aeroponic). Second objective was to compare press pots as propagation medium with nutrient solution as propagation medium. The comparison included DeepFlow water-rooted cuttings with either the stem 1 cm into the nutrient solution or with the stem 1 cm above the nutrient solution. Measurements included fresh weight, dry weight, length, water supply, nutrient supply, and oxygen levels. To account for differences in radiation sum received, crop performance was evaluated with Radiation Use Efficiency (RUE) expressed as dry weight over sum of Photosynthetically Active Radiation. The reference, DeepFlow with substrate-based propagation, showed the highest RUE, even while the oxygen supply provided by irrigation was potentially growth limiting. DeepFlow with water-based propagation showed 15–17% lower RUEs than the reference. NutrientFlow showed 8% lower RUE than the reference, in combination with potentially limiting irrigation supply of nutrients and oxygen. Aeroponic showed RUE levels similar to the reference and Aeroponic had non-limiting irrigation supply of water, nutrients, and oxygen. Water-based propagation affected the subsequent cultivation in the DeepFlow negatively compared to substrate-based propagation. Water-based propagation resulted in frequent transient discolorations after transplanting in all cultivation systems, indicating a factor, other than irrigation supply of water, nutrients, and oxygen, influencing plant uptake. Plant uptake rates for water, nutrients, and oxygen are offered as a more fundamental way to compare and improve growing systems.

ROOT GROWTH OF HORTICULTURAL CROPS AS INFLUENCED BY PINE BARK AGE, WOOD, AND SAND AMENDMENT©

INTRODUCTION When plants are produced in containers their roots are restricted to a small volume; consequently the demands made on the substrate for water, air, nutrients, and support are more intense that those made by plants grown in a field production situation where unrestricted root growth can occur (Bunt, 1988). Vigorous root systems are essential for growth and development of healthy plants. A healthy, functioning root system increases the surface area available for the uptake of water and mineral elements. It is also important to appreciate the fact that root system development, mass and architecture also is critical in providing support, storage and anchorage needed by plants (Jackson et al., 2005; Waisel et al., 2002; Wraith and Wright, 1998). Often excluded from horticultural research, root growth and root system architecture are important factors influencing plant performance and survival (Wright and Wright, 2004). Understanding root growth and development is important to improving plant quality and production success. The capability to observe and measure roots as they grow into a substrate is very useful in determining root growth preference in various substrates. New root measurement techniques have been designed and introduced in recent years which aid in understanding and qualifying root growth of horticultural crops grown in containers (Wright and Wright, 2004; Silva and Beeson, 2011). Pine bark has been the traditional substrate used for the production of nursery crops grown in containers since the 1970s. Both fresh pine bark and aged pine bark have been utilized by growers and analyzed by researchers to determine the best management practices for growing nursery crops (Cobb and Keever, 1984; Harrelson et al., 2004). It is typical that sand is added as an amendment to pine bark for the purpose of adding weight to the container (helps prevent pots from blowing over). Recently, the use/amendment of pine tree substrates (freshly processed loblolly pine wood; PTS) to pine bark has become a trend for some growers and the focus of several researchers (Jackson et al., 2010; Murphy et al., 2010). The effect that these substrate amendments and pine bark age have on root growth in containers is not well known, understood or documented.