Studies on the Evaluation of Climatic Productivity of Paddy Rice

• Published in: Nōgyō kishō Vol. 36; no. 2; pp. 71 - 79
• Main Authors: SUGIHARA, Yasuyuki, HANYU, Juro
• Format: Journal Article
• Language: English
• Published: Tokyo Japan Science and Technology Agency 01.04.1980
• ISSN: 0021-8588; 1881-0136
• DOI: 10.2480/agrmet.36.71

A climatic index, YR, which gives the potential quantity of ripening of the paddy rice, was introduced by Hanyu et al. (1966) as follows: YR=SR{a-b(θR-21.4)2} (1) where, SR denotes the duration of sunshine, θR the mean temperature during ripening period, and a and b are the empirical constants, respectively. The authors attempted to obtain a climatic productivity index of the paddy rice by improving the above index. First, YR as a linear function of SR was modified as follows: YR=ln(1+SR/MO){a-b(θR-θO)2} (2) where, MO is a parameter modifying the slope of YR increase with the increase in SR, and is estimated to be 10 by the manner described after. The constants a and b were estimated to be 260 and 2.70, respectively, from the upper limiting line in Fig. 2 when MO=10, and θO=21.5°C. Both the constants were estimated for the wide range of MO-values, and then the estimated constants were introduced into Eq. (3) to obtain various M-values. The individual M estimated by the actual yield, Y at each area, is equal to or more than MO estimated by YR. As is obvious from Eq. (2), YR decreases with the increase in MO, even if the climatic conditions (SR, θR) during ripening period are suitable. Therefore, it is considered that MO is a variable which is inversely proportional to the sink capacity receiving photosynthetic product before and after heading, and so MO may be accepted as a growth index. Fig. 3 indicates the relationship between the number of grains (N) and M-values obtained by introducing a=260, b=2.70. The limiting curve in Fig. 3 was named MN. The air temperatures prior to heading time, θV and θH were related to M, as shown in Fig. 6. The lower limiting curves in Fig. 6 show the minimum values of M; MV and MH. The larger value between MV and MH was selected as MG. MG was substituted with Eq. (5'). MG was named the "climatic index of growth". The minimum value of MG is MO (=10). YP calculated by Eq. (5) gives the climatic productivity, YP=ln(1+SR/MG){260-2.70(θR-21.5)2} (5) YP was named the climatic productivity index of paddy rice. From the relationship (Fig. 10) between MN and θH, another climatic productivity index, Y'P is given by Y'P=ln(1+SR/M'N){260-2.70(θR-21.5)2} (6) where, M'N is obtained by Eq. (6'). The relationship between YP or Y'P and the actual yield, Y (Figs. 8 & 9) was discussed. The concept on the climatic productivity and its application was previously described by Hanyu et al. (1966).