Analysis of Yield-Determining Process and Its Application to Yield Prediction and Culture Improvement of Lowland Rice : XCIII. Effects of different temperature conditions and fertilizing conditions dufing a nursery period on the growth and characteristics of rice seedlings

Abstract

Combining 6 different temperature conditions (2 different air-temperatures × 3 different water-temperatures) with 6 different fertilizing conditions (3 different levels of fertilizer × 2 different fertilizing soil depths) as shown in Table 1, the authors set up 36 treatments and grew the rice seedlings for 30 days and examined the temperature and fertilizing effects on the growth and characteristics of seedlings. The results obtained can be summarized as follows, 1. The plant age (expressed by the number of leaves on the main stem) is much influenced by the water-temperature, and the higher the temperature is the more the plant age advances but the plant age is also influenced to some extent by the fertilizing conditions such as the amount of nitrogen. 2. The plant height, the weight of top dry-matter and foot dry-matter and the ratio of top dry-matter to the plant height (top/plant height ratio) increase all with the increasing amount of nitrogen as well as the increasing concentration of nitrogen in soil under low air and water- temperatures, while as the temperature raised the ill-effects of large amount of nitrogen on the growth of seedlings begin to appear, and as a result of it, under high temperature conditions it is necessary to decrease the amount of nitrogen as well as the concentration of nitrogen in soil for the favourable growth of rice seedlings. 3. The nitrogen content in rice seedlings is much more influenced by the fertilizing conditions than by temperature conditions, and the nitrogen content is almost parallel to the amount of nitrogen applied. 4. The carbohydrate (total sugar-Estarch) content in rice seedlings is very high in both the highest and the lowest temperature condition in the present experiment and it is very low at the treatment of 26°C in water-temperarature, and it decreases with the increasing amount of nitrogen applied, except for the treatrnent of 36°C in water-temperature. 5. The ratio of carbohydrate to nitrogen (C/N ratio) in rice seedlings is much more influenced by fertilizing conditions than by temperature conditions, and the ratio decreases progressively with the increasing amount of nitrogen applied at any temperature condition.