Sutdies on the Effects of Soil Temperature on Rice Plant Growth : III. Effects of root temperature upon water and nutrients absorptions at different stages and in alternating temperature

Abstract

Effects of root temperature including that of the shoot apex upon absorptions of water and nutrient elements such as N, P and K were examined at different growth stages of a rice plant variety called Norin no. 41. It was experimented using four large-sized thermostats to keep root temperature, at 30°, 25°, 20°and 15°C respectively. Results obtained are summarized as follows: (1) Absorption and transpiration of water due to different root temperatures were checked by lowering of temperature and the minimum value was shown in 15°C plot. (2) Absorption and transpiration of water reduced slightly at 6th leaf stage, but increased at 8th leaf stage in every temperature plot. After that those reduced again at 12th leaf stage, but increased again at 13th leaf stage. (3) Absorption of the three elements showed a similar tendency to water absorption. Generally the maximum value was observed in 25°or 30°C plot, but in the case of N-absorption at the early stages such as 4 and 6th leaf stages, it was odserved especially in 25°C plot. (4) Ratios of nutritive elements to water absorption were in general the highest in 25°C plot and the lowest in 15°C plot. (5) In N-absorption, alternating root temperature was superior to the constant condition. As the alternating condition, it was more favorable that diurnal root temperature was higher than nocturnal root temperature. However, when diurnal root temperature was medium, the absorption was related by nocturnal low root temperature. P absorption was also favorable in variable root temperatures. Under the condition combined with 15°C nocturnal temperature, the absorption was reduced in each case, especially in K absorption.