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.
Fernanda Trientini and Paul R. Fisher
Royal D. Heins and Paul Fisher
Height control is a major challenge in the production of high quality poinsettia crops. Graphical tracking is a technique where growers make height control decisions by comparing actual measured plant height with a desired height. A computer decision support tool, the Poinsettia Care System, is being developed to combine graphical display of plant height with an expert system to provide height control advice. A simulation model is used to predict future growth of the crop based on greenhouse temperature, growth retardant applications, plant spacing, plant maturity, and light quality. Growth retardant and temperature recommendations are made based on a crop's deviation from the target height, expected future growth rate, and crop maturity. The program was beta tested by 8 Michigan growers over the 1991 poinsettia season. The test growers reacted positively to the program in a follow-up survey. Perceived benefits included improved height control, consistent crop recording, and a `second opinion' when making height control decisions. Improvements were suggested to combine the advice of different crops within the same greenhouse zone, to improve the predictive growth model, and to streamline data entry and output.
Erin J. Yafuso and Paul R. Fisher
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.
Ryan W. Dickson and Paul R. Fisher
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.
Elisa Solis-Toapanta, Paul Fisher, and Celina Gómez
To identify practices that may simplify the use of small-scale hydroponic systems for indoor gardening, we compared two nutrient solution management treatments for basil (Ocimum basilicum) production. Experiments were conducted for 8 weeks to evaluate the effect of biweekly replacement of the nutrient solution (W) vs. biweekly fertilizer addition without nutrient solution replacement (W/O) on growth and nutrient uptake of basil ‘Genovese Compact’ grown in either a greenhouse or an indoor environment. Greenhouse day/night temperature was 29/24 ± 4 °C, relative humidity (RH) was 65 ± 4%, and daily light integral (DLI) was 26.1 mol·m‒2·d‒1. The indoor environment had a constant ambient temperature of 21 °C, RH of 65%, and DLI of 9 mol·m‒2·d‒1 provided by broadband white lamps. Four plants were grown in 7.6-L replicate hydroponic systems, with 178 mg·L‒1 N from a complete nutrient solution in two experimental runs. Shoot fresh and dry mass, leaf number, and leaf area showed an increasing quadratic trend over time when plants were grown in the greenhouse. In contrast, growth over time was linear for plants grown indoors. Within each environment, solution management treatment did not affect growth, indicating that the simpler W/O strategy was adequate under these conditions. Plants grown in the greenhouse required more frequent refill water applications compared with indoors, which resulted in three to four times more refill water applied. Because indoor-grown plants had a decreased growth rate, nutrient uptake rate, and volume of water applied compared with plants grown in the greenhouse, electrical conductivity (EC) for the W/O treatment increased over time. Final nutrient solution concentration was highest for indoor-grown plants under the W/O treatment, and final tissue nutrient concentration was higher for plants grown indoors compared with the greenhouse. Final nutrient uptake (dry mass × nutrient concentration) was higher for plants grown in the greenhouse rather than indoors. Considering that EC increased in the solution of indoor-grown plants under W/O, an appropriate strategy using this treatment would require reducing fertilizer input indoors. To refine simple and robust fertilizer management strategies for indoor gardeners, further research is needed to test variables such as different plant species, cultivars, and water qualities.
Dustin P. Meador and Paul R. Fisher
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.
John M. Dole, Paul Fisher, and Geoffrey Njue
Several treatments were investigated for increasing vase life of cut `Renaissance Red' poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch.) stems. A vase life of at least 20.6 days resulted when harvested stems were placed directly into vases with 22 °C deionized water plus 200 mg·L-1 8-HQS (the standard floral solution used) and 0% to 1% sucrose without floral foam. Maturity of stems at harvest, ranging from 0 to 4 weeks after anthesis, had no effect on vase life or days to first abscised leaf. Pretreatments immediately after harvest using floral solution heated to 38 or 100 °C, or 1 or 10-min dips in isopropyl alcohol, had no effect, whereas 24 hours in 10% sucrose shortened vase life by 6.4 days and time to first abscised cyathium by 4.5 days. Stem storage at 10 °C decreased vase life, particularly when stems were stored dry (with only 0.8 days vase life after 3 weeks dry storage). Increasing duration of wet storage in floral solution from 0 to 3 weeks decreased vase life from 21.5 to 14.6 days. Placing cut stems in a vase containing floral foam decreased time to first abscised leaf by 3.7 to 11.6 days compared with no foam. A 1% to 2% sucrose concentration in the vase solution produced the longest postharvest life for stems placed in foam but had little effect on stems not placed in foam. A 4% sucrose concentration decreased vase life compared with lower sucrose concentrations regardless of the presence of foam. Holding stems in the standard floral solution increased vase life and delayed leaf abscission compared with deionized or tap water only, with further improvement when stem bases were recut every three days. Commercial floral pretreatments and holding solutions had no effect on vase life and days to first abscised cyathium but delayed leaf abscission.
Paul R. Fisher and Royal D. Heins
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.
Caroline S. Donnelly and Paul R. Fisher
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-2·d-1 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.
Kathryn M. Santos, Paul R. Fisher, and William R. Argo
The objective of this study was to quantify water volume and nutrient content leached during propagation of herbaceous cuttings in commercial greenhouses. Nutrient concentrations in the fertigation solution, substrate, tissue, and leachate were measured between Jan. and Mar. 2006 at eight greenhouse locations in Michigan, Colorado, New Hampshire, and New Jersey. Grower management of the timing and concentration of nutrients applied to vegetatively grown calibrachoa (Calibrachoa ×hybrida) or petunia (Petunia ×hybrida) liner trays varied among the eight locations, ranging from 0.5 to 80 mg·L−1 nitrogen (N) in week 1 and from 64 to 158 mg·L−1 N in week 4. Over a 4-week crop period, applied nutrients averaged 4.9 g·m−2 N, 0.8 g·m−2 phosphorus (P), and 5.8 g·m−2 potassium (K), and leached nutrients averaged 1.1 g·m−2 N, 0.3 g·m−2 P, and 1.6 g·m−2 K. Leaching of nutrients and irrigation water was highly variable among locations. Leached water volumes ranged from 4.5 to 46.1 L·m−2 over 4 weeks and contained 0.29 to 1.81 g·m−2 N, 0.11 to 0.45 g·m−2 P, and 0.76 to 2.86 g·m−2 K. The broad range in current commercial fertigation practices, including timing of nutrient supply, concentration of applied fertilizer, and leaching volume, indicate considerable potential to improve efficiency of water and fertilization resources during propagation and reduce runoff.