水稲の生育及収量と水温との関係についての現地調査

抄録

The auther classified in the previous paper the paddy fields in the Shichigashuku Village, Miyagi Prefecture from the standpoint of the temperature of irrigation water into the following four groups:
paddy area irrigated with water of low temperature (Max. water temp. below 20°C on Aug. 18)
do. of semi-low temperature (Max. 20-23°C on Aug. 18)
do. of medium temperature (Max. 23-25°C on Aug. 18)
do. of high temperature (Max. over 25°C on Aug. 18)
In each area, the representative paddy fields irrigated continuously with water or respective temperature were selected and the growth and yield of rice-plant therein were observed in relation to the water temperature. The results obtained were described and discussed in this paper.
(1) In each paddy field of all the area, the growth and yield of rice increased as the distance from the inlet of water became larger, just same as the temperature of water rose. But the ratio of the increase became less, so that the correlation curve between the increase of growth or yield and the distance from the inlet was parabolic, not linear.
(2) On the growth and yield of rice, the area of high water temperature predominated particularly over the other three. From the point of temperature, water of below 20°C gave serious cold injury to the plant and made almost all of spikelets sterile. The plant was also affected considerably by the water of 20 to 25°C, and especially the temperature of 20 to 22°C was distinguished with the remarkable falling down of the grouth and yield. Incidentally, it was conseivable that that this extent of water temperature would be critical to the growth of rice-plant. On the other hand, water of over 26°C influenced very little and that of over 28°C wo uldnt be troubled about the injurious effect to the plant under somewhat bad climatic conditions.
(3) The fertility of heads was also affected by the temperature of water irrigated. Dividing all the kernels into complete grains (wholly ripened) and incomplete ones (the others), the number or percentage of the former was increased in proportion to the distance from the inlet with just same patterns as mentioned in (1), and the tendency was particularly distinct in the area of low water temperature.
And besides, the ripening appearences in corresponding parts, for instance, water inlet of fields in each area were related with the water temperature; say, excellent in the the high temperature area and in turn.
On the contrary, the incomplete grains did not show so distinct tendency as the complete ones.
(4) Water temperature influenced differently on each tillering of the plant. By a certain degree of low temperature the main culm was injured the least; the higher the order of the tillering, the more the cold injury, general.
At the part of fields where water temperature was about 25°C, heads of both main culm and 1st-ordered tillers had almost same fertillity. Where it was about 24°C, heads of main culm had almost all of complete grains and a little of incomplete ones, while those of 1st-ordered tillers had about half of complete and incomplete grains. Below 23°C, the majority of grains remained to ripen incompletely.
(5) The above-mentioned results of field observations on the relation between the water temperature and the growth or yield of riceplant seemed to concur with many results of laborateory experiment already reported.