Studies on the Microclimate in the Vegetations of Tame Pastures in Summer : I. On the effect of irrigation, pasture mixture and clipping on the soil temperature In pastures : II. On the daily variations of air temperature and relative humidity in the vegetations and on the evapo-transpiration of orchardgrass and ladino clover

Abstract

The daily variations of air temperature, soil temperature and relative humidity in the vegetations of tame pastures and evapo-transpiration of some pasture crops were measured from the stand point to diminish the summer depression. At the same time, the effects of irrigation, pasture mixture and clipping on the soil temperature were investigated.: The results are summarized as follows: 1. Soil temperature; (1) Irrigation: Maximum soil temperature at surface, 5 cm and 15 cm depth was lowered by 3°C, 2°C and 1°C respectively by irrigation when the soil was dry and air temperature was high. (2) Pasture mixture: Maximum soil temperature at 5 cm depth in ladino clover stand was 1°C higher than that in both orchardgrass and orchardgrass-ladino clover mixture. That in orchardgrass-ladino clover mixture was 2°C higher than that in both orchardgrass-ladino clover-Italian ryegrass mixture and orchardgrass-ladino clover-alfalfa mixture. These tendencies were distinct in clear day when the soil was drier or the air temperature was higher. Therefore it is supposed that the maximum soil temperature was affected by the soil moisture content. (3) Clipping: The maximum soil temperature at 5 cm depth in clipping plot of ladino clover was about 3°C higher than that in non clipping plot, while the maximum air temperature in the former was 3°C lower than that in the latter. It is considered from these results that the soil temperature can be controlled by irrigation, pasture mixture and clipping. 2. Daily variation of temperature; The remarkable vertical distribution of air temperature was shown in the vegetation. Especially, the air temperature at 2 cm height reached 35∼37°C in daytime, which was 3.5∼7.0°C higher than that of standard air temperature and was maintained 2°C higher during night. The growing points of these pasture crops might be placed under such condition as some degrees higher than standard air temperature. 3. Relative humidity and the moisture contents of soil and plant leaves; Relative humidity became lower in the daytime than in the morning and evening. Moisture contents of soil and plant leaves showed the same tendencies. 4. Evapo-transpiration; Evapo-transpiration per unit leaf area of ladino clover was more than that of orchard grass. Evapo-transpiration increased exponentially with rise of temperature.