Studies on the Relation of the Weather Conditions to the Growth of Crops

Part 1. Relation of the Air Temperature to the Heading date of rice plant (1)

Abstract

In order to establish plans of cultivation of crops, the laws of response of environment to the growth of crops should be clarified. In the thorough investigation of the relation of weather conditions to the growth of rice plant, the writers divided the growth into phase and quantity. The relationship between air temperature and the heading date among phases was analysed.
Hours(t) found in each class interval of air temperature in a day were calculated by using model of the diurnal variation of air temperature in Japan already obtained (Table 1-A). Then, the daily sum of the product of t and average air temperature in each class interval resulted in the daily mean air temperature (θ₀, Formula (1)) and the sum of θ₀ ranging from the transplanting to the heading date resulted in the accumulated air temperature (Σθ₀) for that period (Formula (2) and Table 1-B). From the fact that Σθ₀ increases under high or low air temperature condition and decreases in the intermediate air temperature condition, the velosity of growth causing heading (V) was thought to be related with air temperature (θ), as shown in Formula (3). Then, γ is a constant which is independent of both V and αθ. And moreover α is a coefficient of air temperature effective for causing heading or effective air temperature coefficient and it is a function for air temperature. Integrating Formula (3) from the transplanting (t=0) to the heading (t=t(h)), Formula (4) is obtained. When the phases of growth (S_o, S_h) at the times of transplanting and heading are constant, ∫^t(h)_oαθdt becomes constant, and is expressed approximately by the Formula (5). Σθ* means effective accumulated air temperature. From the experimental results during six years at the Aomori Agricultural Experiment Station (Kuroishi City) and Fujisaka Farm, accumulated air temperature for each temperature class was calculated by the Formula (2). Assuming that α changes continuously by the air temperature, αθ was obtained by multiplying average air temperature for each class by the coefficient adequate for the α value. Σθ* was obtained by accumulating αθ from the transplanting to the heaping. Σ^t(h)_i=0θ* of which coefficient of variation shows the smallest value, means the effective accumulated air temperature peculiar to a given variety. α value satisfactory for the effective accumulated air temperature was called as the effective accumulated air temperature coefficient peculiar to a given variety (Fig. 2). θ* calculated by multiplyin effective air temperature coefficient thus decided by θ value was called as the equivalent of air temperature necessitat ing for the growth causing heading (Fig. 3).
The calculated heading date, when the effective accumulated air temperature was acquired for the first time by accumulating daily θ* from the time of transplanting, agrees well with the actual heading date (Table 4). The heading date can be assumed by summing θ* from the transplanting to a given date (A) before the heading date and the expected θ* from the date (A) to the heading, and also by the average air temperature θ0 during sixty days after transplanting date and uneffective accumulated air temperature Σθ′(=Σθ₀-Σθ*). As for the latter assuming method, the relationship between Σ^t(h)_i=0θ_Li′and θ₀ shown by Fig. 5 or Formula (10) was obtained. Here, Σ^t(h)_i=0θ_Li′ means the uneffective accumulated air temperature