The effect of container porosity on root environment and plant growth
SummaryComparison of clay and plastic pots for tomato propagation in six experiments showed plastic pots to give significantly better results than clay pots in winter and the converse to be true in summer. In each experiment the ratio of plant growth (dry weight) in clay and plastic pots was related to both the mean daily solar radiation and the mean outside night minimum temperature. In winter, plants in both types of container made significantly more growth when stood on open benches than when stood on benches with solid surfaces.These differences in growth were related to soil temperature, clay pots being cooler than plastic pots, the temperature difference between the types of pot ranging from approximately 1°C by night in winter to 4°C under high intensity solar radiation in summer. In winter, soil temperatures were often below the optimum, and in summer in excess of the optimum.By day, temperature within the pots showed highly significant correlation with solar radiation, and by night in winter pot temperature was negatively correlated with the difference between the glasshouse and the outside air temperature.Well-defined horizontal thermal gradients were found, and these were positively correlated with soil temperature. In wet soils the thermal gradients were less than in dry soils, and because of their higher thermal conductivity wet soils were warmer than dry soils.When the normal evaporative cooling from the porous walls of clay pots was prevented by a bituminous coating, the soil temperature during the night was not significantly different from that in plastic pots. By day, however, soil temperature in non-evaporating clay pots was less than that in evaporating clay pots, due to the lower thermal conductivity of the dry clay wall.
The effect of container porosity on root environment and plant growth
SummaryThe effect of container porosity on water relations in the substrate and on plant growth was examined. With clay containers the proportional effect of the wall on water loss varied with season, being responsible for 42 per cent of the total loss in winter and 25 per cent in summer. Water loss from plastic containers was 55 per cent of that from clay containers in winter, and 66 per cent in summer. Wall porosity also had a significant effect on water distribution within the container under high radiation conditions.Tomato plants grown under three water regimes showed no effect of matric stress in winter, but growth was significantly reduced for each increase in stress in summer. There was no interaction between container type and water stress.Non-porous containers gave a higher water-use efficiency and had a lower irrigation requirement than porous ones, their greatest advantage being under conditions of low transpirational loss and high evaporative loss.
An evaporation experiment and its irreversible thermodynamics
Abstract This paper considers a particular heat and water vapor transfer problem in a nonisothermal steady state system. The results are applicable to a condition that may develop during the normal drying of porous materials. The rate equations are based on the theory of irreversible thermodynamics and the validity of Onsager's reciprocity relation is demonstrated with a macroscopic analysis of this particular model. The results of an experiment are presented which show the effects of temperature, pressure, and salt concentration on the evaporation and heat transfer from a porous plate. These data combined with the thermodynamic flux equations provide a means of calculating the effective concentration of dissolved salts at the air-water interface and the approximate depth of this increased concentration. The analysis also provides a method for determining the rate-limiting process in the experiment.