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.
Yield Potentials of Rice and Soybean As Affected by Cropping Systems in Mid-mountainous Paddy Soils of Korea
To get some informations for sustainable paddy use, the productivities of soils with two years of cropping systems were estimated through pot experiment using two pretreated groups of not autoclaved ‘natural’- and ‘autoclaved’-soils without any fertilization. And then the relationship between the productivities, called yield potentials, and the characteristics of soils as affected by cropping systems, such as rice-rice (R-R), rice-barley-rice-barley (R-B-R-B), rice-barley-rice-wheat (R-B-R-W), soybean-barley-soybean-barley (S-B-S-B), of which barley and wheat were composted at a level of 10 MT ha -1 , and S-B-S-B without compost, was analyzed. These treatments were established in mid-mountainous loam paddy, which contained exchangeable Ca of 11.8 cmol c kg -1 , located at the altitude of 285 m above sea level in Sangju of Korea. Crops for the estimation of soil productivity were rice cv. ‘Seolemi’ and soybean cv. ‘Chamol’. As a result, under the natural soils condition, rice grain and straw were highly produced in composted S-B-S-B soils ( p < 0.05) and lowly in R-R soils ( p < 0.05). While soybean grain and stem were higher in R-R soils ( p < 0.05) than other soils which not significantly different each other. In case of autoclaved soils, the yield potentials of rice and soybean were high together in either composted R-B-R-B/W or S-B-S-B soils compared to R-R and uncomposted S-B-S-B soils ( p < 0.05). In especial, these yield potentials under the natural soils condition were commonly influenced by soil porosity showing negative correlation for rice ( p < 0.01); positive for soybean ( p < 0.05). And the porosity possibly reversed even the symbiotic contribution of indigenous Bradyrhizobium japonicum for soybean. Under autoclaved soils condition the potentials of rice and soybean showed negative correlations with soil C:N ratio ( p < 0.05) similarly to the case of rice in the natural soils.
Gill diseases of cultured salmonids in Ontario.
Between 1977 and 1981, the Fish Pathology Laboratory of the Ontario Veterinary College received 239 cases from trout farms of southern Ontario, 51 (21.3%) of which had diseased gills. Branchial lesions in 86.3% of these 51 cases were characterized by marked lamellar epithelial hyperplasia with epithelial hypertrophy and lamellar fusion. Filamentous bacteria were seen on the surface of the branchial filaments and lamellae in 68.6% of the cases. Our observations highlight the importance of gill diseases as a production problem of farmed salmonids in southern Ontario.