The irrigation in rice-field should be reasoonably regulated according to the growth stage of crop, the climate, and the locality.
In this paper, the influences of irrigating methods upon the soil-temperature are investigated.
The daily-range decreasing index (p) of soil-temperature and the thermal-diffusibility (a2) derived from the observed date (Table 1) are shown in Table 2.
If the heat were transported only by conduction without any of convection or “Austausch” in ideal static pool, the thermal diffusibility aw2 and the range-decreasing index pw would be respectively 0.0016cm2/sec. and 0.15 when calculated with thermal-conductivity of water. The values of p (0.11 & 0.13) in the surface strata of real field are fairly close to pw.
If a2 is calculated by formula (6) with each volume, thermal-conductivity, specific-heat, and density of soil and watdr, it almost occords with a2 value 0.003 of surface stratum in Plot A; and it increases as the volume of soil increases, Formulae (6) & (8).
The thermal effects of water in rice-field are so great, that the limits of soil-temperature which follow that of water-temperature are made favorable to the crop by regulation of irrigation.