Analysis of Yield-Determining Process and Its Application to Yield-Prediction and Culture Improvement of Lowland Rice : CVII. Effects of different air temperature, soil temperature and soil moisture during the nursery period on the growth and the characteristics of rice seedlings

Abstract

To investigate the proper environmental condition for the healthy growth of rice seedlings, 24 treatment plots were set up in this experiment, combining 6 different temperature conditions (2 different air temp. ×3 different soil temp.) with 4 different soil moisture levels. The effects of temperature and soil moisture on the growth and characteristics of rice seedlings were examined at the age of 6.5 in leaf-number. The seedlings harvested at the age mentioned above were transplanted and grown under a low temperature condition, and the rooting ability was examined 10 days after the transplanting. The following are the results obtained in this experiment: (1) The leaf-emergence rate was mainly influenced by the temperature, and was hardly affected by the soil moisture as far as a relatively low temperature (16∼21°C) was concerned. However, the effect of soil moisture was gradually appeared as the temperature was raised up. (2) The plant height, the dry weight, the nitrogen content and the carbohydrate content in rice seedling were more strongly influenced by the temperature than the soil moisture. (3) On the other hand, the number of roots and water content in the seedling were more influenced by the soil moisture than the temperature, and were increased with the raise of soil moisture. (4) The number of tillers was apparently influenced by both soil temperature and soil moisture. The optimum soil moisture which produced the maximum number of tillers at each temperature condition was different, i.e. the soil moisture of 100% was the optimum at 21°C/air×16°C/soil and at 21°C/air×21°C/soil, and 80% was the optimum at 21°C/air×26°C/soil, 31°C/air×26°C/soil, 31°C/air×31°C/soil and 31°C/air×36°C/soil. (5) The following conditions combined soil temperature with soil moisture, i.e. 16°C/soil×60%/soil and 21∼36°C/soil×40%/soil were respectively suitable for the vigorous rooting under the low temperature condition. (6) In the nursery period, the combinations of 26°C or 31°C in soil temperature and 80% in soil moisture caused the poor rooting under the low temperature condition. It was pointed out from the results mentioned above that the proper soil moisture management as well as temperature management is quite necessary for raising of healthy seedlings. Therefore, the importance of the soil moisture management, especially in the high temperature condition, should be emphasized.