Studies on Cool Injury in Bean Plants : V. Effects of rates and sources of phosphate fertilizer on the growth and yield of soybeans as subjected to low temperature from early to mid-reproductive stage

摘要

1) This experiment was carried out to examine the effects of phosphate fertilization on the growth and yield of soybeans subjected to low temperature, at 15°C day and night, under the natural light condition of a glasshouse in the phytotron, for 15 days (L-1), or 3O days (L-2), from about three days before the onset of the flowering of the controls grown in a glasshouse, similar to the open. The plants were grown in a 1/2000-a Wagner pot, filled with about 10 kg of a volcanic ash soil, which is high in the coefficient of phosphate absorbance and lacking in the available phosphate, with and without phosphate fertilization. Either fused phosphate or superphosphate was applied at the rate of 6 g or 18 g per pot. 2) As the phosphate rate increased, seed yield increased in all of three growing conditions. However, the magnitude of reduction in seed yield caused by low temperature treatments was greatest at the 6 g application. No significant difference in seed yield was obtained between fused phosphate and superphosphate at the same fates of application. 3) At the 6 g application, the decrease in seed yield caused by the low temperature treatments was mainly due to the decrease in pod number and pod setting rate of the flowers on branches. 4) The plants applied with superphosphate showed better vegetative growth at early stages and set more flowers in contrast with the plants grown in the same rates of fused phosphate. On the contrary, the plants with fused phosphate produced significantly higher 100-seed weight than those with superphosphate did. These differential responses in yield components might be due to the differential speed of acting of the phosphate fertilizers used. 5) Concentration of phosphorus in leaves and stems was determined for the samples taken at the 15th day under 15°C condition and corresponding samples taken from the control condition. Compared with controls, the concentration of phosphorus in leaves and stems of the plants grown under 15°C condition was lower in minus phosphate plots, kept at the same level at the 6 g application and higher at the 18 g application respectively. 6) The plants grown in the highest rate of phosphate showed best growth during the low temperature treatment and smoothly regained from the stress after the end of treatment. The major cause of yield decrease in the 6 g plots was due to incomplete recovery of growth after the treatments, which resulted from insufficient phosphrus accumulation in the plants throughout the development especially during the period under the low temperature. 7) There were high positive relationships between the seed weight and stem weight or between pod number and node number on branches. Both of the regression equations calculated separately with control or L-2 plots were quite similar. The correlation coefficients for seed yield and stem weight or for the pod number and node number on branches, when the coefficients were pooled with the control and L-2 plots, were 0.962 and 0.966 significant at 0.1% level respectively. It was apparent that the excellent vegetative growth insures better yield even in the L-2 plots. High phosphate application to volcanic ash soils would be effective in reducing the poor-growth type of injury stressed by unfavorable conditions including cool summer weather, through improving the growth of soybeans.