Crop scientfic studies on the yield-forecast of lowland rice (Preliminary report) : IX. Effects of light intensity at important growing stages of rice on the yield and yield-constitutional factors

摘要

In 1951 and 1952, authors made experiments, controlling the sunlight with white clothes of various kinds of texture, to ascertain to what extent the yield of rice and its 4 constitutional factors are affected by different light intensity. The experiments were carried out in paddy field with 4 randomized blocks. Classes of light intensity used were 4 in 1951, and 1952. Results obtained are summarized as follows : (1) No definite relations between light intensity and number of heads per unit area were obtained. (2) Definite relations of light intensity to number of spikelets per head and weight of 1, 000 grains were found for the period 15 days prior to heading, especially for the period 12 6 days prior to heading, and those to fruit bearing percentage were found for the period 15 days immediatly after h heading. Each relation found was represented by a quadratic equation. By knowing the light intensity expressed in calorie/cm2. day, and using the equations one may easily calculate the value of eachfactor which determines the yield. (3) A very important fact was drawn from the relations mentioned above ; that is, there exists a indispensable and sufficient level of light intesity for not to reduce the values of the factors and the amount of grain yield, namely, about 340 cal./cm2. day. Light intensity higher than this proved of no direct use in favouring the yield and its constitutional factors. And the light intensity higher than 240 cal./cm2 has a little effect on reducing them. Lower light intensity than 240 cal./cm2, however reduces decidedly the rice-yield and values of the yield constitutional factors in proportion to the reduction of light intensity. (4) It may not be said that the same relations as obtained in the present experiments always exist in other places with different ecological conditions or with different varieties, but analogous relations would be likely obtained in every case. Therefore, the study on the relation of light intensity to yield and its constitutional factors seems td offer some promising contribution for predicting yield of rice.