Impact of Alternative Materials on Container Physical Properties and Substrate Temperature

Studies were conducted at the University of Kentucky to evaluate side wall water loss and substrate temperature of quart size alternative containers derived from paper, card board, peat, cow’s manure, rice hull or coir, bio degradable plastic, and plastic (control). An environmental chamber controlled for temperature and relative humidity was used to obtain a VPD of 2.6 k Pa. The containers were filled to their rim with saturated Fafard potting mix. Top part of each container was sealed using plastic sheet to prevent evaporation through the open surface.  Five replicates of containers were moved to the chamber and hourly substrate water loss was measured. Another five replicates were used to determine light reflectance, wall temperature and substrate temperature in room temperature at 20⁰C and relative humidity 50%. Two 100 watts incandescent bulbs were installed 6 inches away from pots to provide heating for 90 minutes to warm up the substrate. After 90 minutes, radiation flux density of pot side wall was measured using a pyranometer (Licor-LI200). After measuring the radiation, the light was turned off, the temperature of pot wall was determined using an Infra-Red thermometer. Substrate temperature was obtained at one inch depth of the substrate at the center of pot and between the pot side wall and center of pot.

It was found that on an average plastic and bio-plastic containers lost 2.5 ml water whereas containers manufactured using rice hull, coir and straw containers lost 10 to 20 ml and peat, wood pulp and cow manure containers lost 25 to 30 ml in an eight hour period in the chamber. Light reflectance was lowest for black containers (20Wm^-2) and it was higher for all alternative containers and it varied around 70 to 120 Wm^-2 for rice, coir and straw containers. Container wall temperature was highest for plastic and bio-plastic containers (40ºC) followed by rice hull, coir and straw containers (30 ºC) and peat, wood pulp and cow manure based containers showed lowest wall temperature of around 24 ºC.  Substrate temperature near to sidewall was highest for plastic and bio-plastic (28ºC), followed by all other alternative containers (22 ºC), same trend was noticed for temperature at the center of the container with plastic showing the highest (25ºC) and all alternative containers showing lower values (21ºC). Light reflectance and porous nature of container walls prevented higher substrate temperature buildup of some of the alternative containers.