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Claudia Calonje, Chad Husby, and Michael Calonje

of cycads. In the current study, two other substrates, Turface®, a calcined montomorillinite clay (Turface® MVP®; Profile Products LLC, Buffalo Grove, IL), also known as arcillite, and coarse silica sand (6/20 grade; Florida Silica and Sand Company

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Kimberly A. Williams and Paul V. Nelson

Soilless container media have almost no capacity to retain PO4 or K. The nutrient retention of two calcined clays, attapulgite and arcillite, and brick chips, precharged with PO4 and K, was investigated. These could serve as an alternative slow-release fertilizer when incorporated into a soilless medium as a component of the mix. Sorption curves were developed at 25 °C for attapulgite of two particle sizes (0.8 to 1.6 mm and 1.6 to 3.2 mm), arcillite (1.1 to 3.2 mm), screened pieces of brick (1.0 to 3.6 mm), and a medium of 7 sphagnum peat: 3 perlite (v/v) using solutions of KH2PO4 (P at 0 to 20,000 mg.L-1). Curves indicated that PO4 and K sorption were similar for both particle sizes of attapulgite, so only the larger size [1.6 to 3.2 mm (8 to 16 mesh)] was used in greenhouse studies. Materials were evaluated in greenhouse studies by growing 'Sunny Mandalay' chrysanthemum [Dendranthema ×grandiflora Kitam. (syn. Chrysanthemum morifolium Ramat.)]. The precharged materials were tested at 10%, 20%, and 30% by volume of a peat: perlite root medium. Phosphate, K, and pH were determined on unaltered medium solutions collected throughout the cropping cycle and foliar analyses were determined on tissue collected at midcrop and end of the crop. Data indicated that precharged calcined clays retained and released PO4, and to some degree K, over time. Precharged clays did not provide K at levels which met plant needs during the latter half of the cropping cycle, but it was released and used at appreciable levels during the first month of crop production. Growth of plants receiving PO4 solely from precharged attapulgite and arcillite at 20% of the medium volume was not significantly different from that of a commercial control when the leaching fraction was maintained at 0.2. However, release of PO4 from the brick chips was not enough to match plant demand. Phosphate lost through leaching from the precharged clays was reduced by about two-thirds compared to control plants fertilized with P at 46.5 mg.L-1 from water-soluble fertilizer at each watering.

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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.

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Ted E. Bilderback, Stuart L. Warren, James S. Owen Jr., and Joseph P. Albano

Many research studies have evaluated potential organic and mineral container substrate components for use in commercial potting substrates. Most studies report results of plant growth over a single production season and only a few include physical properties of the substrates tested. Furthermore, substrates containing predominantly organic components decompose during crop production cycles producing changes in air and water ratios. In the commercial nursery industry, crops frequently remain in containers for longer periods than one growing season (18 to 24 months). Changes in air and water retention characteristics over extended periods can have significant effect on the health and vigor of crops held in containers for 1 year or more. Decomposition of organic components can create an overabundance of small particles that hold excessive amounts of water, thus creating limited air porosity. Mineral aggregates such as perlite, pumice, coarse sand, and calcined clays do not decompose, or breakdown slowly, when used in potting substrates. Blending aggregates with organic components can decrease changes in physical properties over time by dilution of organic components and preserving large pore spaces, thus helping to maintain structural integrity. Research is needed to evaluate changes in container substrates from initial physical properties to changes in air and water characteristics after a production cycle.

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Kimberly A. Williams and Paul V. Nelson

Soilless substrates have little capacity to sorb PO4. One way to reduce PO4 leaching during production is to increase the substrate retention of PO4. Adsorption isotherms were created at 25 C for alumina (aluminum oxide); the 2:1 calcined clays arcillite (montmorillonite plus illite) and attapulgite.; and a medium of 70 peat: 30 perlite using solutions of KH2PO4 at rates of P ranging from 0 to 20000 μg·ml-1. Material sorbed at the rate resulting in maximum P adsorption was then desorbed 22 times. Sorbing concentrations necessary to establish an equilibrium P concentration of 10 μg·ml-1 in the substrate solution were estimated from these curves. Materials were-charged with P at these estimated rates and evaluated in a greenhouse study in which each material was tested at 10 and 30% by volume of a 70 peat: 30 perlite substrate used to produce Dendranthema × grandiflorum `Sunny Mandalay'. Phosphate, K, and pH were determined on unaltered soil solutions biweekly throughout the cropping cycle and foliar analyses were determined on tissue collected at mid- and end-crop. Isotherm and greenhouse data indicated that alumina, arcillite, and attapulgite effectively retained and slowly released K as well as PO4 over time. Alumina was most effective at retaining P, sorbing 16800 μg/cc compared to 3100 and 7800 μg P sorbed/cc for arcillite and attapulgite, respectively, when sorbed at P concentrations resulting in an equilibrium concentration of approximately 10 μg P/ml.

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T.W. Tibbitts, J.G. Croxdale, C.S. Brown, and R.M. Wheeler

Leaf cuttings from 6-week-old potato plants were planted into the Astroculture flight unit for the STS-73 shuttle flight in Oct. 1995. Tubers developed in the axils of the five leaf cuttings during the 16-days in microgravity. The flight unit had a closed growth chamber maintained at 22°C, 82% relative humidity, 150 μmol·m–2·s–1 photosynthetic photon flux, and with carbon dioxide controlled during the light period to ≈400 μmol·mol–1 and exceeding 4000 μmol·mol–1 during the dark period. A controlled delivery system using a porous tube system in arcillite medium provided water to the cuttings. A camera mounted in the top of the chamber provided video images of the plants at 2-day intervals. The cuttings maintained good vitality for the first 12 days of the flight followed by senescence of the leaves. Tubers 1.5 cm in diameter and weighing 1.7 g were produced. The shape and size of the tubers, the internal cell arrangement, and the size range of the starch grains, were similar on cuttings developed in a control experiment on the ground. Also the concentrations of starch, sucrose, fructose, glucose, and total soluble protein in the cuttings from space were similar to the cuttings developed on the ground. The challenges in scheduling experiments in a space flight and in conducting comparison control experiments on the ground are discussed. Environment control variations associated with cabin pressure changes, venting requirements, and air sampling are reviewed.

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Gary W. Stutte and Greg Goins

In preparation for a spaceflight experiment to measure photosynthesis of wheat (PESTO), four solid media were evaluated for use in the rooting modules of the Biomass Production System (BPS), a new plant growth unit for microgravity. The media were commercial peat-vermiculite (PV) mixture, zeolite developed at Johnson Space (Z/JSC), commercial zeolite developed by Boulder Innovative Technologies (Z/BIT), and arcillite (AR) with slow-release fertilizer. Wheat (cv. USU Super Dwarf) was grown in the media at 1500 μmol/mol CO2, 350 μmol·m-2·s-1 PAR, 23 °C, and 75% relative humidity for 18 to 21 days. Water was delivered to the media through porous tubes imbedded in the media, and NDS pressures of -0.1 to -0.5 kPa were maintained with either a static or recirculating standpipe. Plant height, leaf area, and fresh mass were determined for each experiment. Results indicated that the AR and Z/BIT media resulted in larger and more uniform plants than Z/JSC or PV at the same NDS pressure. Additional experiments were conducted with AR to evaluate interactions between particle size and NDS pressure. At ≈14 days after planting, there was a loss of NDS prime in AR >2.0 mm when the NDS pressure was less than -0.3kPa. This resulted in drying of the media and poor plant growth. There was excess water in the media, which resulted in reduced plant size, in AR <1.0 mm at NDS pressures more than -0.3 kPa.

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Desmond Mortley, Jill Hill, Conrad Bonsi, Walter Hill, and Carlton Morris

Tuskegee University is conducting research on salad crops as part of the National Aeronautics and Space Administration's (NASA) goal of supporting humans on near-term space missions, such as on the International Space Station. Small areas of salad crops are ideal candidates for growing in limited volumes, and would provide a source of fresh food to enhance the crew's nutrition. Baseline controlled environment studies were initiated to evaluate the response of eight carrot cultivars (`Baby Mini', `Nantes Touchan', `Danvers 126', `Kundulus', `Nanco Hybrid', `Thumbelina', `Early Nantes', and `Juwarot') to growth and yield in hydroponics. Seeds were sown in moist arcillite and transplanted into growth troughs (0.15 × 0.15 × 1.2 m) after 18 days in reach-in growth chambers, and nutrients continuously supplied by a half-Hoagland solution. Growth chambers conditions included 300 μmol·m-2·s-1 photosynthetic photon flux, 16/8 photoperiod, a constant 25 °C and relative humidity of 50%. Plants were harvested at about 80 days. All eight cultivars grew well in the hydroponic system. Seven cultivars produced greater shoot fresh than root mass except `Baby Mini', which showed the reverse. `Danvers 126', followed by `Nanco Hybrid' and `Nantes Touchan', produced highest root yields. The β-carotene content varied by cultivars. The highest level of 10,400 IU/100 g was obtained for `Thumbelina', followed by `Baby Mini' (8040 IU/100 g), `Juwarot' (6160 IU/100g), and `Early Nantes' (5210 IU/100 g), and the lowest by `Nantes Touchan' (3510 IU/100 g). These results show that while carrots adapted well to growth in hydroponics, carotene, a major nutrient, was at relatively low levels.

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James S. Owen Jr, Stuart L. Warren, Ted E. Bilderback, and Joseph P. Albano

in bark and peat-based substrates ( Handreck and Black, 2002 ; Reed, 1996 ). Empirically, Warren and Bilderback (1992) compared rates (0, 27, 54, 67, and 81 kg·m −3 ) of arcillite in a pine bark substrate and reported arcillite increased available

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James S. Owen Jr, Stuart L. Warren, Ted E. Bilderback, and Joseph P. Albano

. Williams and Nelson (1997) investigated various clays (palygorskite and arcillite) and brick chips as precharged sources of P in peat:perlite substrates. The palygorskite clay absorbed 77% more P than the other materials. In a subsequent study, P leachate