title: Physical and hydraulic properties of baked ceramic aggregates used for plant growth medium.
abstract: 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 approximately 65%, substantially lower than total porosity of approximately 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 approximately 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 approximately 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.
authors.affiliation: Universities Space Research Association, NASA/JSC, Houston, TX 77058, USA.
authors.forename: Susan L
authors.initials: SL
authors.lastname: Steinberg
authors.forename: Gerard J
authors.initials: GJ
authors.lastname: Kluitenberg
authors.forename: Scott B
authors.initials: SB
authors.lastname: Jones
authors.forename: Nihad E
authors.initials: NE
authors.lastname: Daidzic
authors.forename: Lakshmi N
authors.initials: LN
authors.lastname: Reddi
authors.forename: Ming
authors.initials: M
authors.lastname: Xiao
authors.forename: Markus
authors.initials: M
authors.lastname: Tuller
authors.forename: Rebecca M
authors.initials: RM
authors.lastname: Newman
authors.forename: Dani
authors.initials: D
authors.lastname: Or
authors.forename: J Iwan D
authors.initials: JI
authors.lastname: Alexander
mesh_terms: D000538:Aluminum Silicates; D002516:Ceramics; D000077215:Clay; D003470:Culture Media; D018504:Ecological Systems, Closed; D018527:Hydroponics; D008021:Life Support Systems; D010316:Particle Size; D018517:Plant Roots / Q000254:growth & development / Q000378:metabolism; D016062:Porosity; D012212:Rheology; D012987:Soil; D013026:Space Flight; D014867:Water; D014893:Weightlessness
chemical_list: D000538:Aluminum Silicates; D003470:Culture Media; D012987:Soil; D014867:Water; D000077215:Clay