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.
Circulation of Water in Soil under a Temperature Gradient
SEVERAL workers (for example Gurr et al.1, Hutcheon2) have suggested that, when a temperature gradient is applied to a uniform closed soil column, a circulatory system is set up, and that any eventual steady moisture distribution is actually a dynamic balance of opposing fluxes, predominantly vapour from hot to cold, and predominantly liquid from cold to hot. In this communication we show that, at equilibrium, a static system cannot exist, and confirm experimentally the existence of a circulatory system.
Note on the Relation between Growth of Roots and of Tops in Wheat
STUDIES in the experimental morphology of plants have dealt mainly with the subaerial portions, comparatively little attention having been paid to variations in the growth of roots. Thus the literature of the subject is very meager. Several authors, especially MOELLER,, DETMER,2 PERSEKE,3 MER,4 GAIN,5 and FREIDENFELT,6 have studied the relation of water to the growth of these organs, with the general result that in water itself they grow longer and thinner, with fewer branches and root hairs than are observed in moist soils. Curiously enough, in soils which are too dry for optimum growth, the response is very similar. The roots are long and slender and possess few branches excepting near their tips, which lie, of course, in moister soil. The only observation on the relation of root growth to that of tops, with which the writer is acquainted, is that of MOELLER, to the effect that in a series of nutrient solutions, of concentrations ranging from I .0 to 0.05 parts per thousand, the actual weight of roots produced varies generally with the concentration, but that the ratio of weight of roots to that of tops is much larger in the most dilute solution than in any of the others. A number of experiments have suggested to the author that the accel-