Diurnal Variation Characteristics of Sap Flow in Kimchi Cabbage and of Air Temperature and Relative Humidity near the Surface of Cultivated Soil

In this study, sap flow of Kimchi cabbage was affected the most by solar radiation, but it was not completely consistent. In addition, it was judged to be somewhat affected by other weather environmental factors such as temperature, soil temperature, wind speed, relative humidity, and vapor pressure deficit. Sap flow of Kimchi cabbage was affected by changes in soil temperature in the root stalk and solar radiation in the leaves. The effect of soil moisture on sap flow was not sensitive in the range of available soil moisture conditions, while it showed different patterns according to the measurement location, leaf aging, and extreme weather conditions. The ratio of evapotranspiration calculated from sap flow and from the positive relationship between them was presented as an irrigation signal. When the soil moisture was sufficient, the temperature and humidity measured at the top 1 cm of the ground surface adjacent to the cabbage followed the general pattern of temperature and humidity change in the air, and the opposite result was obtained when the soil moisture was insufficient. Therefore, it was determined that the abnormal change signal of the temperature and humidity near the surface of the Kimchi cabbage cultivated soil can be used as an indicator for determining the soil moisture state.