To test the effects of fertilizer concentration and growth medium electrical conductivity (EC) on the growth of New Guinea impatiens (Impatiens sp. hybrids or I. platypetala Lindl.), plants of `Selenia' were grown 70 days in a commercial soilless medium and irrigated with solutions of 20N-4.3P-16.6K at concentrations of 0.5, 1.0, 1.5, or 2.0 g·liter-1. In a fifth treatment (“delay”), no fertilizer was applied for the first 14 days after planting, then 0.5 g·liter-1 was applied for the next 14 days, followed by 1.0 g·liter-1 until the end of the experiment. Measurements of shoot dry weight and growth medium EC were made at 14-day intervals. Differences in dry weight between fertilizer treatments became significant (P = 0.0001) 42 days after planting. Over the 70-day experiment, plants grew most with 0.5 g·liter-1 and delay treatments. High fertilizer concentrations (1.5 and 2.0 g·liter-1) caused the most growth suppression and resulted in increasing growth medium EC with time. An EC of ≈1.5 dS·m-1 or higher was associated with suppressed growth beginning 42 days after planting. A mild chlorosis developed on the leaves of some plants at the two highest fertilizer concentrations.
Laura K. Judd and Douglas A. Cox
Garrett Goyette and Wallace Pill
The utility of Ironrich (IR), a tertiary mineral co-product from TiO2 production, as a growth medium component was investigated. All complementary bulking components (10 to 50% volume) gave reduced shoot fresh weights of tomato, impatiens or perennial ryegrass relative to Fairgrow (FG, co-composted solid waste and sewage sludge). Shoot fresh weights of impatiens and tomato grown in 50% IR with FG were similar to those grown in commercial peat-lites. When provided 200 mg N litre-1 daily, chard shoot fresh weights, beet root fresh weights, and tomato fruit fresh weights from plants grown in 50% IR plus 50% FG were not significantly different from those grown in 50% silt loam plus 50% FG. Tissue Cd, Cr, Ni, and Pb concentrations from plants grown in 50% combinations of FG with IR or silt loam were below the limits of detection. IR plus FG with N-P-K fertilization provided a satisfactory greenhouse growth medium. We project that IR + FG will constitute a satisfactory synthetic topsoil.
Rita L. Hummel, Shiou Kuo, Diane Winters and Eric Jellum
A fish waste/hemlock-fi r sawdust compost (FWC) was evaluated as a container growth medium and N source for the greenhouse production of marigold (Tagetes patula `Queen Sophia') and geranium (Pelargonium xhortorum `Sprinter Scarlet') in 10-cm containers. Treatments were a factorial set of three Douglasfir bark (B)/three FWC mixtures (100% FWC; 50% FWC/50% B; 100% B) and three rates of N fertilizer (0, 300 and 600 ppm N) applied every 2 weeks. After the initial irrigation, plants were drip-irrigated to negate leaching from the containers.
Weekly measurements of leachate conductivity, pH, and inorganic N were made on additional replications of the 0-ppm N plants in all growing media. Plant height and width were measured at 2-week intervals and, at the end of the production cycle, flower number, shoot fresh and dry weight, visual quality, and root dry weight were measured. The growing medium by N interaction was significant for all variables. Results indicated that plants receiving 0 ppm N in 100% FWC were larger and of higher quality than plants in 100% B receiving 600 ppm N. In 100% FWC, marigold shoot growth, dry weight, and quality were not influenced by N rate. The observed geranium and marigold growth response indicated that FWC was an effective N source and growing medium when leaching was minimized with drip irrigation.
Maria Papafotiou, Barbara Avajianneli, Costas Michos and Iordanis Chatzipavlidis
resource that should be preserved. A parallel environmental issue is the disposal of agricultural wastes. Composts from agricultural wastes have the potential to replace a significant proportion of peat in the growth medium of potted ornamentals ( Burger et
Luisa Dalla Costa, Nicola Tomasi, Stefano Gottardi, Francesco Iacuzzo, Giovanni Cortella, Lara Manzocco, Roberto Pinton, Tanja Mimmo and Stefano Cesco
spinach plants when the sulfur (S) availability in their growth medium is limited ( Prosser et al., 2001 ). The unbalanced acquisition of these elements could be ascribed either to their low soil availability or by an impaired root capability to drive
Susan L. Steinberg, Gerard J. Kluitenberg, Scott B. Jones, Nihad E. Daidzic, Lakshmi N. Reddi, Ming Xiao, Markus Tuller, Rebecca M. Newman, Dani Or and J. Iwan D. Alexander
Baked ceramic aggregates (fritted clay, arcillite) have been used for plant research both on the ground and in microgravity. Optimal control of water and air within the root zone in any gravity environment depends on physical and hydraulic properties of the aggregate, which were evaluated for 0.25-1-mm and 1-2-mm particle size distributions. The maximum bulk densities obtained by any packing technique were 0.68 and 0.64 g·cm-3 for 0.25-1-mm and 1-2-mm particles, respectively. Wettable porosity obtained by infiltration with water was ≈65%, substantially lower than total porosity of ≈74%. Aggregate of both particle sizes exhibited a bimodal pore size distribution consisting of inter-aggregate macropores and intra-aggregate micropores, with the transition from macro- to microporosity beginning at volumetric water content of ≈36% to 39%. For inter-aggregate water contents that support optimal plant growth there is 45% change in water content that occurs over a relatively small matric suction range of 0-20 cm H2O for 0.25-1-mm and 0 to -10 cm H2O for 1-2-mm aggregate. Hysteresis is substantial between draining and wetting aggregate, which results in as much as a ≈10% to 20% difference in volumetric water content for a given matric potential. Hydraulic conductivity was approximately an order of magnitude higher for 1-2-mm than for 0.25-1-mm aggregate until significant drainage of the inter-aggregate pore space occurred. The large change in water content for a relatively small change in matric potential suggests that significant differences in water retention may be observed in microgravity as compared to earth.
M. Papafotiou, G. Kargas and I. Lytra
Research was carried out to evaluate composted olive-mill waste as a peat substitute in foliage potted plant production. Rooted cuttings of Codiaeum variegatum (L.) A. Juss and Syngonium podophyllum Schott were grown for 5 months and Ficus benjamina L. for 10 months in media containing olive-mill waste compost (OWC), sphagnum peat and perlite in 1:3:4, 1:1:2, and 3:1:4 ratio (by volume), respectively, and their foliage and root growth was determined and compared to a control medium of 1 peat: 1 perlite (by volume). When up to 75% of peat in the control medium was replaced by OWC, C. variegatum foliage and root growth were similar compared with the control, while a 50% peat replacement gave the best growth. Syngonium podophyllum was more sensitive to peat replacement compared to C. variegatum, as only 25% of peat could be replaced by OWC without any reduction in foliage growth. The dry weight of the roots was not affected in all media tested. In F. benjamina, peat could be replaced up to 75% without effects on plant height and lateral shoot number, while the length of the laterals was progressively reduced with increasing OWC level. However, only at the highest OWC level (75% peat replacement) the laterals were shorter compared with the control. There was also a progressive reduction of main stem diameter, foliage fresh weight, and root dry weight with increasing OWC level in the medium. Even the lowest OWC level (25% peat replacement) caused a decrease of foliage and root weight compared with the control, with no effect though on plant visual quality. Even a 25% peat replacement by OWC caused an increase in bulk density. A considerable decrease of total porosity and readily available water were measured in media where 50% or 75% of peat was replaced by OWC. The pH of the medium with the highest OWC level was high during the first 4 months of culture compared to the other media. The electrical conductivity initially related to OWC level, but it decreased to values similar to that in the control medium during the first month of culture.
Leslie K. Manning, Robert R. Tripepi and Alton G. Campbell
Postharvest plant residues from Kentucky bluegrass (Poa pratensis L.) seed production may be useful as an organic amendment in container mixes. Postharvest residues of `South Dakota' bluegrass were composted with and without an N amendment, such as cattle manure (M) or alfalfa seed screenings (As). After composting, all residues were ground to 4- to 6-mm segments and mixed with sphagnum peat and perlite (2:1:1 by volume). Media that contained amended bluegrass residues had higher electrical conductivity (EC) values and lower C: N ratios (<19:1) than media made with other bluegrass residues. Tomato (Lycopersion esculentum Mill. `Laura') seedlings grown in residue composted with As had at least 3.5- and 4-fold more shoot dry weight and leaf area, respectively, than plants grown in any other composted medium. In addition, seedlings grown in composted bluegrass residues amended with As had 34% and 41% more shoot dry weight and leaf area than plants grown in a 75% peatmoss–25% perlite medium. Composted residue amended with alfalfa seed screenings appears to be suitable as a peatmoss extender in container media.
Chris A. Martin and Dewayne L. Ingram
A three-dimensional computer model was developed to simulate numerically the thermal environment of a polyethylene container-root medium system. An energy balance was calculated at the exterior container wall and the root medium top surface. Thermal energy exchanges at the system's boundaries were a function of radiation, convection, evaporation, and conduction energy flaxes. A forward finite difference form of a transient heat. conduction equation was used to calculate rates of temperature changes as a result of thermal energy exchanges at the system's boundaries. The χ2“goodness-to-fit” test was used to validate computer-generated values to actual measured temperature data. Probabilities for the null hypothesis of no association ranged from P = 0.45 (Julian day 271), to P = 0.81 (Julian day 190), with P ≥ 0.70 on nine of 10 validation days in 1989. Relative to net radiation and convection, conduction and evaporation had little effect on thermal energy exchanges at the root medium top surface during sunlight hours. The rate of movement of thermal energy (thermal diffusivity) was slower and generally resulted in lower temperatures in a pine bark medium than in a pine bark medium supplemented with sand when volumetric water content (VMC) ranged from 0.25 to 0.45.
Valtcho D. Zheljazkov, Thomas E. Horgan, Tess Astatkie, Dolores Fratesi and Charles C. Mischke
filled with growth medium (Metromix 300; Sun Gro Horticulture, Bellevue, WA). When plants reached 6 to 8 cm, they were transplanted in 3-gallon 1400 series pots. The experiment was conducted in a greenhouse at the North Mississippi Research and Extension