Effects of the Amount of Nitrogen Absorbed up to the Stage of 90 in Leaf Number Index on the Morphological Characteristics, the Degree of Lodging and the Yield Components in Rice Plants

Abstract

Under various conditions such as culture in gravel, framed soil and paddy field, rice plants (var. Manryo) were grown at the different levels in the nitrogen amount of basic dressing and top-dressing at young panicle formation stage for 8 years from 1964 to 1971. The dry weight and the nitrogen content of rice plants from 252 treatments in all were determined at the stages of 70 and 90 in leaf number index. After the measurement of the length of upper three leaves, culm and lower three internodes, the degree of lodging and the yield components at the maturity, the author tried to clear the effect of the amount of nitrogen absorbed by rice plants on the above mentioned characteristics. Results obtained were summarized as follows: 1. Both the amount of nitrogen absorbed up to the stage of LNI 70 (N1) and of nitrogen absorbed during the period of LNI 70-90 (ΔN=N2-N1) facilitated the elongation of upper three leaves and lower three internodes, and increased the degree of lodging. In this instance these effects of N1 were larger than those of ΔN, while in the case where N1 was divided into the dry weight (W1) and the nitrogen content (n1), these effects of W1 were also larger than those of n1. 2. To maintain the degree of lodging less than about 3.0 in the case of about 500 in the number of panicles per square meter, it was required that the length of upper three leaves, culm and lower three internodes was less than about 130, 80 and 15 cm, respectively. 3. For the purpose of restricting the characteristics within limits mentioned above, it seemed that following conditions were necessary; a) N1 was less than 7g/m2, b) W1 less than 200g/m2 and c) ΔN less than 4-6g/m2. Consequently, it was supposed that the upper limit of the amount of nitrogen absorbed up to the stage of LNI 90 (N2) was about 11g/m2 under the conditions of this experiment. 4. The schematic diagram of the mutual relation among above mentioned factors was proposed and the relative effect of these factors on those which were located in the direction indicated by the arrow was estimated