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The objective was to quantify the effect of water-soluble fertilizers on concentration of free chlorine level in a sodium hypochlorite solution. Research on the disinfestation strength and phytotoxicity risk of chlorine compounds is needed, because control of waterborne pathogens has been based on response to free chlorine, whereas dual injection of fertilizer and chlorine is a common horticultural practice. Free chlorine from sodium hypochlorite was applied at 2.6 mg·L⁻¹ chlorine (Cl) to deionized water only (control) or deionized water with 11 nutrient solutions at 200 mg·L⁻¹ nitrogen (N). Nutrient solutions included reagent-grade ammonium sulfate (NH₄)₂SO₄, ammonium nitrate (NH₄NO₃), potassium nitrate (KNO₃), and urea salts and seven commercial blended N–P–K water-soluble fertilizers that contained both macro- and micronutrients. Commercial fertilizers contained ammonium-N at 0% to 50% of total-N, urea-N at 0% to 14% of total-N, and nitrate-N at 50% to 93% of total-N. Free Cl (mg·L⁻¹), total Cl (mg·L⁻¹), and oxidation-reduction potential (ORP, in mV) were measured 2 min and 60 min after Cl was applied. Combined Cl was calculated as the difference between the total and free Cl measurements. All solutions were maintained at pH 6 and 25 °C. In the control solution, free Cl was 2.6 mg·L⁻¹ after 2 minutes and decreased to 2.2 mg·L⁻¹ after 60 minutes. The ammonium-containing solutions (NH₄)₂SO₄ and NH₄NO₃ resulted in free Cl below 0.1 mg·L⁻¹ after 2 minutes. Urea reacted more slowly than ammonium salts, whereby free Cl decreased to 2.3 mg·L⁻¹ after 2 minutes and 0.4 mg·L⁻¹ after 60 minutes. In contrast, KNO₃ had less impact on free Cl with 2.4 mg·L⁻¹ free Cl available at both 2 minutes and 60 minutes. With all commercial fertilizers tested, free Cl decreased after 2 minutes to below 0.1 mg·L⁻¹. Total Cl remained above 2 mg·L⁻¹ after 60 minutes in all treatments, indicating that the majority of Cl was in a combined form for ammonium and urea salts and commercial fertilizers. The ORP of commercial fertilizer blends and ammonium-containing salts was lower than 600 mV, whereas deionized water, KNO₃, and urea treatments had ORP levels above 650 mV. Nutrient solutions containing ammonium or urea required 20 mg·L⁻¹ or more of applied Cl to provide residual free Cl above 2 mg·L⁻¹ at 2 minutes.

Oxygen supply to the root zone is essential for healthy plant growth, and one technology that can potentially supply additional oxygen is the injection of purified oxygen (oxygenation) into irrigation water. The objective was to evaluate whether oxygenation of irrigation water affected plant growth and substrate dissolved oxygen (DO) levels during mist propagation of unrooted cuttings and subsequent growth in containers. Dissolved oxygen measured at source tanks for ambient tap water (averaging 7.1 mg·L⁻¹) or oxygenated tap water (31.1 mg·L⁻¹) was pumped through fine (69 µm) mist nozzles for propagation of Calibrachoa ×hybrid ‘Aloha Kona Dark Red’ and Lobelia erinus ‘Bella Aqua’. There were no measured differences in root length or root dry mass for Calibrachoa and Lobelia propagated using oxygenated water compared with ambient water because DO of ambient or oxygenated water reached ≈100% oxygen saturation in water (8.7 mg·L⁻¹) after passing through mist nozzles. To evaluate subsequent growth without the effect on DO of fine emitters, rooted cuttings of these two plant species and Pelargonium ×hortorum ‘Patriot Red’ were grown in 10.2-cm diameter pots. The plants were irrigated with either ambient (6.0 mg·L⁻¹) or oxygenated (27.7 mg·L⁻¹) nutrient solutions, delivered by top watering or subirrigation when the substrate dried to ≈45% of container capacity (CC), measured gravimetrically. Oxygenated water did not enhance root or shoot growth compared with ambient water for the three bedding plants. In addition, Pelargonium growth was not enhanced when irrigated at high moisture level (maintained at 80% CC) with oxygenated water compared with ambient water. In container substrate without plants, it was possible to increase DO of the substrate solution by 68% when a high volume of oxygenated water (200% container volume or 850 mL) was applied by top watering because existing substrate solution was displaced. In contrast, when containers were subirrigated at 45% CC, the smaller 180-mL volume of oxygenated water was absorbed by the substrate and did not increase DO compared with ambient water. Overall, irrigating with oxygenated water did not enhance root or plant growth of three bedding plants grown in porous, peat-based substrate. To increase oxygen supply to roots in container production, growers should focus on having adequate air porosity in substrate and avoiding overwatering.

Small-scale hydroponics is a growing urban horticulture trend, but nutrient solution management remains a challenge for small growers. The objective was to investigate the potential to use controlled-release fertilizer (CRF) to simplify nutrient management in small-scale hydroponic systems. Three experiments were conducted with the goal of a single fertilizer application during the crop cycle of basil (Ocimum basilicum). Nutrient release curves were quantified by adding prills to water and measuring nutrient content weekly in the solution for CRF products without plants. In all seven products tested (Osmocote Bloom 2–3M, Osmocote Plus 3–4M, E-Max Calcium Nitrate 2–3M, Agrocote MAP 3–4M, E-Max Keiserite 3–4M, E-Max K-Mag 2–3M, and Agrocote SOP 3–4M) an initial rapid release was followed by a plateau, but release rates differed between products varying from 100% (MgSO₄) to 60% release [(NH₄).(H₂PO₄)] over an 11-week evaluation period. Total nutrient content in two commercial N–P–K CRF products (3–4 months 15N–3P–10K and 2–3 months 12N–3.1P–14.9K) provided lower Ca and Mg compared with a typical hydroponic solution based on water-soluble fertilizer (WSF). A subsequent experiment evaluated plant growth response using the same two commercial CRF products (single application) or a WSF (replaced weekly) in growth chamber environment. Plants grown for 4 weeks under CRF treatments yielded less than half the shoot fresh weight of plants grown with WSF and exhibited symptoms of Ca deficiency and micronutrient toxicity (confirmed with tissue analysis). Electrical conductivity (EC) of CRF solutions increased over time indicating excess dose compared with plant uptake, reaching a maximum of 5.4 dS·m⁻¹. Nutrient release curves from the first experiment were then used to estimate product release and create a single-application nutritional program based on a customized “Blend” developed from CRF macronutrients plus WSF micronutrients. Plants were grown hydroponically with two dosages of Blend (1X and 2X) and compared with a commercial WSF with weekly replacement of solution. Blend 2X and WSF treatments had similar shoot fresh weight (241 and 244 g/four plants, respectively) with healthy plant appearance and tissue nutrient levels generally within published survey ranges for basil. Commercial CRF products designed for soil or container production were unsuitable for hydroponics, but acceptable plant performance with the customized CRF Blend demonstrated proof-of-concept for a single CRF application.

Objectives were 1) to quantify acidic and basic effects on the root zone pH for eight vegetable and herb species grown in peat-based substrate and hydroponic nutrient solution and 2) to determine the applied NH₄ ⁺:NO₃ ^– ratio expected to have a neutral pH reaction for each species during its vegetative growth phase. In one experiment, plants were grown for 33 days in substrate (70% peat:30% perlite by volume), and were fertilized with a nutrient solution containing 7.14 milli-equivalents (mEq)·L^–1 N and NH₄ ⁺:NO₃ ^– ratios ranging from 0:100 to 40:60. During the second experiment, the same species were grown in hydroponic nutrient solutions at 7.14 mEq·L^–1 N with NH₄ ⁺:NO₃ ^– ratios ranging from 0:100 to 30:70, and data were collected over a 6-day period. In substrate, species increased root zone pH when supplied 0:100 solution, except for cucumber, which did not change substrate pH. Increasing the NH₄ ⁺:NO₃ ^– ratio to 40:60 increased acidity and decreased pH across species. Similar trends were observed in hydroponics, in which the most basic response occurred across species with 0:100, and the most acidic response occurred with 30:70. Arugula was the only species that increased root zone pH with all three NH₄ ⁺:NO₃ ^– ratios in substrate and hydroponics. In substrate and hydroponics, mEq of acidity (negative) or basicity (positive) produced per gram dry weight gain per plant (mEq·g⁻¹) correlated positively with mEq·g⁻¹ net cation minus anion uptake, respectively, in which greater cation uptake resulted in acidity and greater anion uptake resulted in basicity. In hydroponics, the greatest net anion uptake occurred with 0:100, and increasing the NH₄ ⁺:NO₃ ^– ratio increased total cation uptake across species. Cucumber had the most acidic effect and required less than 10% of N as NH₄ ⁺-N for a neutral pH over time, arugula was the most basic and required more than 20% NH₄ ⁺-N, and the remaining species had neutral percent NH₄ ⁺-N between 10% and 20% of N. Increasing the NH₄ ⁺:NO₃ ^– ratio decreased Ca²⁺ uptake across all species in hydroponics, which could potentially impact tip burn and postharvest quality negatively. Controlling root zone pH in substrate and hydroponic culture requires regular pH monitoring in combination with NH₄ ⁺:NO₃ ^– adjustments and other pH management strategies, such as injecting mineral acid to neutralize irrigation water alkalinity or adjusting the limestone incorporation rate for substrate.

A methodology based on process-control approaches used in industrial production is introduced to control the height of poinsettia (Euphorbia pulcherrima L.). Graphical control charts of actual vs. target process data are intuitive and easy to use, rapidly identify trends, and provide a guideline to growers. Target reference values in the poinsettia height control chart accommodate the biological and industrial constraints of a stemelongation model and market specifications, respectively. A control algorithm (proportional-derivative control) provides a link between the control chart and a knowledge-based or expert computer system. A knowledge-based system can be used to encapsulate research information and production expertise and provide management recommendations to growers.

The objective was to quantify the effect of supplemental lighting on cutting production for 10 herbaceous annual cultivars. Stock plants of four cultivars (Heliotropium arborescens `Atlantis', Petunia `Supertunia Sun Snow', Scaevola aemula `New Wonder', and Verbena `Tapien Soft Pink') received ambient light [average 6.2 mol·m^-2·d^-1 photosynthetic photon flux (PPF) during the photoperiod], or ambient light plus either 1.6 or 2.8 mol·m^-2·d^-1 PPF from high-pressure sodium (HPS) lamps for 11 hours. In a second experiment, the same four species plus six other cultivars were grown under ambient light (average 7.9 mol·m^-2·d^-1 PPF) or ambient plus 1.9 mol·m^-2·d^-1 PPF from HPS. The effect of HPS on the production of cuttings varied greatly between species. Growth of Heliotropium was not significantly affected by light level in either experiment. In the first experiment, the addition of 1.6 mol·m^-2·d^-1 PPF from HPS increased the number of Petunia `Supertunia Sun Snow', Scaevola, and Verbena cuttings by 14%, 51%, and 12%. The addition of 2.8 mol·m<sup>-2</sup>·d<sup>-1</sup> PPF from HPS, increased cuttings harvested from these three species by 23%, 73%, and 22% respectively. In the second experiment, Petunia `Supertunia Sun Snow', Scaevola, Aloysia triphylla (lemon verbena), and Osteospermum `Lemon Symphony' had a positive cutting production response to HPS (17% to 45% increase), whereas cutting numbers of other species (Argyranthemum `Summer Melody', Lantana `Patriot Firewagon', Impatiens New Guinea hybrid `Pedro', Petunia `Supertunia Blue Wren', and Verbena) were not significantly affected by HPS. In both experiments, cutting quality (length, stem caliper, fresh mass, and dry mass) and subsequent rooting of cuttings were not significantly affected by light level.

The objective was to quantify the effect of substrate pH and micronutrient concentration on growth and pigment content for two floricultural crop species, Petunia ×hybrida `Priscilla' and Impatiens wallerana `Rosebud Purple Magic'. A 70% peat: 30% perlite medium was amended with dolomitic hydrated lime to achieve five substrate pH's ranging from pH 4.4 to 7.0. Plants were grown in 10-cm-diameter pots in a greenhouse for 4 weeks, and irrigated with a fertilizer containing (in mg·L^-1) 210N-31P-235K-200Ca-49Mg. Micronutrients were applied using an EDTA (ethylenedinitrilotetraacetic acid) chelated micronutrient blend (C111), at 1×, 2×, and 4× concentrations (in mg·L^-1) of 0.50Fe-0.25Mn-0.025Zn-0.04Cu-0.075B-0.01Mo. Petunia shoot dry mass and stem caliper decreased as substrate pH increased, whereas leaf length and width remained unchanged. The highest level of C111 resulted in higher dry mass and smaller leaf area compared with other C111 levels. Overall, substrate pH and C111 had little effect on plant size or mass for impatiens. For both species, increasing substrate pH above 5.3 resulted in a decline in chlorophyll, carotenoids, and the SPAD chlorophyll index (measured with a Minolta-502 SPAD meter) compared with the lowest three pH levels. Chlorosis was observed at pH 7 after 2 weeks of growth. Increasing C111 concentration had no effect on pigment content below pH 5.3, but increased pigment content at higher pH levels. The SPAD index was highly correlated with chlorophyll content. This research emphasizes that an acceptable range in substrate pH can vary depending on fertilizer practices, with higher micronutrient concentration compensating for lower solubility at high substrate pH.

The objective was to quantify the effect of substrate pH and micronutrient concentration on tissue nutrient levels in Petunia ×hybrida Hort. Vilm.-Andr. and Impatiens wallerana Hook. F. Plants were grown in 10-cm-diameter pots for 4 weeks in a 70% peat: 30% perlite medium amended with five lime rates to achieve substrate pH values ranging from pH 4.4 to 7.0. Plants were irrigated with (in mg·L^-1) 210N-31P-235K-200Ca-49Mg. Micronutrients were applied as an EDTA (ethylenedinitrilotetraacetic acid) chelated micronutrient blend (C111), at 1×, 2×, and 4× concentrations of 0.50Fe-0.25Mn-0.025Zn-0.04Cu-0.075B-0.01Mo. Patterns of tissue concentrations across substrate pH differed from nutrient solubility in the medium, particularly with regard to Mn. Foliar N content decreased slightly as substrate pH increased, whereas foliar Ca, Mg, and S increased. Although foliar P and K varied with pH, there was no consistent trend between species. Foliar total Fe, ferrous Fe, and Cu decreased as substrate pH increased, whereas foliar Zn increased. Foliar Mn content decreased for both species as pH rose to 6.0, and then increased from pH 6.0 to 7.0. In contrast, Mn level in the substrate, measured in a saturated medium extract using deionized water as the extractant, decreased as pH increased from pH 4.4 to 7.0. Chlorophyll content decreased when the ratio of tissue Fe to Mn was <0.57 (impatiens) or <0.71 (petunia), or Fe was <106 (impatiens) or 112 (petunia) μg·g^-1. SPAD chlorophyll index also declined in petunia with foliar Mn >42 μg·g^-1. Increasing C111 increased foliar Cu, total Fe and ferrous Fe in both species, and B for impatiens, and partly compensated for reduced nutrient solubility at high pH.

Nutrient uptake during adventitious root formation is not clearly understood, resulting in variable fertilization strategies in propagation and increased potential for nutrient deficiency or nutrient runoff. The objective was to quantify rooting response to fertility treatments and tissue nutrient concentration changes in response to basal or apical nutrient supply during three rooting phases in propagation of Petunia ×hybrida ‘Supertunia Royal Velvet’ and ‘Supertunia Priscilla’ stem tip cuttings. One of two treatments [a complete fertilizer solution (in mg·L⁻¹) 56 NO₃-N, 19 NH₄-N, 13 phosphorus, 88 potassium, 39 calcium, 28 magnesium, 20 sulfur, 11 sodium, 1.1 iron, 0.5 manganese, 0.5 zinc, 0.25 copper, 0.29 boron, 0.1 molybdenum, and 0.01 aluminum] or clear tap water was applied to the cuttings. Tissue N–P–K concentrations declined as plant development increased from Stage 0 to 3 regardless of fertilizer treatment or location applied. Foliar application of N–P–K during propagation maintained tissue nutrient concentration at higher levels before Stage 2 (initial root emergence) compared with plants that received clear water only; however, overall, a decline in concentration was measured from Stage 1 to Stage 3. Measurable N–P–K uptake occurred during root development from the foliar and basal portions of the cuttings. Basal fertilizer applications resulted in increased root length and root number compared with plants treated with clear water. These results emphasize that nutrient uptake occurs from both the stem and foliar portion of Petunia cuttings, and nutrient availability at the stem base at root emergence improves root development.

Unreacted residual limestone in the container substrate is key in buffering pH change over time. Our goal was to develop a substrate test protocol to measure residual lime [in units of CaCO₃ equivalent (CCE)] by applying a strong mineral acid (HCl) to a substrate sample and measuring the evolved CO₂ gas with a gasometric method based on a Chittick apparatus. In one experiment, CaCO₃ was added to a substrate that had previously been neutralized to pH 7.35 with Ca(OH)₂ so that there would be minimal CaCO₃ reaction with the substrate at this high pH. The gasometric method was then used to estimate residual CCE. Measured CCE and applied CaCO₃ were similar, indicating reliable CCE estimation. In a second experiment, a pH titration method was used to quantify the relationship between substrate-pH and milliequivalents of reacted base and provided an additional validation of the estimated reacted and residual CCE. The gasometric method demonstrated declining residual CCE over time as a dolomitic limestone reacted to raise substrate-pH and increasing residual CCE as applied CaCO₃ concentration increased. Residual CCE in a substrate is an important property that should be considered for pH control and management in greenhouse crop production. Our results indicate that the gasometric system may be useful for optimizing lime application rate, lime source, or management of residual CCE during crop production.