An observation of various temperatures influenced by windbreak net was carried out at the paddy rice fields in Naganuma, Hokkaido from June 22 to July 1, 1978. As the decreasing effect of windspeed has been considerably recognized by many other references until now, an investigation was done only on a subject of various temperatures, i.e., leaf, air, water and ground temperatures.
The following results were obtained.
Under the condition of overcast weather and “cutoff” flood irrigation system on June 22, the increasing rates of temperatures are 0.3 to 1.0°C for t_l (surface leaf-stem temperature) and 0.8 to 1.6°C for t_w (surface water temperature) measured by precision radiation thermometer at the point from -2H (distance represented windbreak height) (minus sign denotes windward side) to 10H. The reference temperature denotes the value at the point of -20H.
In the case of clear weather and “cutoff” flood irrigation system on June 23 to 24, the increasing rates of temperatures are 0.2 to 1.4°C for t_l, 0.9 to 2.3°C for t_w, 0.3 to 1.0°C for T_l (leaf temperature), 0.2 to 0.9°C for T_a (air ternperature), 0.9 to 2.2°C for T_w (water temperature) and 0.9 to 2.0°C for T_g (ground temperature) measured by thermo-junction thermometer. Maxima of temperature differences between 2H and 30H were 2.7°C for t_l at 1700 June 23, 3.8°C for t_w at 1515 June 23, 2.0°C for T_l at 1220 June 24, 2.8°C for T_w at 1220, 3.5°C for T_a at 1300 June 23 and 3.8°C forT_g at 1300.
Under the circumstance of overcast weather and “continuous” flood irrigation system on June 30 and July 1, the increasing rates of temperatures are 0.2 to 0.6°C for t_l, 0.5 to 1.0°C for t_w, 0.4 to 1.1°C for T_l, 0.3 to 1.0°C for T_a, 0.8 to 1.1°C for T_w and 0.8 to 1.1°C for T_g.
An interesting result was come up that the increasing temperatures at the distance of 1H just behind the windbreak were lower than those at the distances of -2H and 2H, i, e., the values from 0800 to 1230 for t_l, from 1200 to 1515 for t_w, from 1300 to 1720 for T_l and from 2230 to 0630 for T_w, and the greater parts of values from 0920 to 1720 for T_a and from 1220 to 0330 for T_g. This seems to be mainly based on the reason that the adiabatic cooling wind of pretty high speed blows through the open space of 25cm between the net and the ground, and the increments of latent and sensible heat fluxes by increasing windspeed.
The temperature difference for t_wl on June 22 is 1.7 to 2.7°C and ones for t_wl and T_wl are 3.1 to 4.1°C and 3.7 to 5.1°C, respectively, T_la is -0.0 to 0.4°C at the points from 1H to 20H and T_gw at the points from 5H to 7.5H is 0.1 to 0.2°C and-0.1 to-0.5°C at other points, particularly -0.9°C at 1H on June 23 to 24. The value of t_wl, T_wl, T_la and T_gw are 2.2 to 2.6°C, 2.3 to 2.5°C, 0.1 to 0.3°C and 0.1 to 0.5°C on June 30 and July 1, respectively.
According to the observation results mentioned above, it is considered that the region considerably effected by windbreak is from 5H in the windward side to 20H in the leeward side.
The appearances of maximum and minimum of t_l, T_l and T_a are generally earlier than thoseof t_w

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The energy balance of stems of rice plants provided a method by which the apparent thermal conductivity of the stem can be evaluated in relation to the rate of water flow in the stem. In this method, the influence of sensible heat transfer between the stem surface and ambient air on the propagation of temperature wave in the stem was taken rigorously into consideration. Water loss evaluated from the theoretical relation was found to agree well with the transpiration loss of water measured directly by weighing potted rice plant. This good agreement indicates that the newly developed method could be applicable to the measurement of the apparent thermal conductivity of the stem and the rate of upward flow of water in the stem due to transpiration.
The apparent thermal conductivity of the stem increased with the increment of the rate of upward water flow in the stem, particularly in a range of water flow higher than 0.003 cm/sec. This implies that the influence of cool flooding water on the thermal regime in rice plants becomes larger in daylight hours than at night. The method was also used to make clear the diurnal course of the rate of water flow in the rice stems under field conditions.

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