Characteristics And Influencing Factors Of Soil Condensation Water In Loess Hilly And Gully Region

The soil condensation water,as one of the sources of non-rainfall water inputs on the land surface,plays an active role in improving the surface environment and maintaining the stability of the ecosystem because of its high frequency,long duration and occurrence in the dry season without rainfall.In this paper,a typical pilot was selected in the Loess hilly and gully region,and three small lysimeters with soil depths of 5,10,20 cm were set up in the test site by using the weighing method to monitor the change of soil condensation water at different depths under the bare soil condition for one year.In addition,the effects of meteorological factors and soil factors on soil condensation characteristics was explored combined with the in-situ experiments.The sources of soil condensation water vapor in the Loess hilly and gully region were explored simultaneously by deploying open-ended,top-sealed and bottom-sealed micro-lysimeters at 5,10 and 20 cm depths around the instrument.The following conclusions were mainly obtained:(1)Soil condensation water in the Loess hilly and gully region mainly occurs in the soil below the surface at a depth of 5 cm,and the amount of condensation gradually decreases as the soil depth increases.The total annual soil condensation water in the soil layer at a depth of 5 cm reached 12.59 mm,accounting for 1.69% of the annual rainfall(743.4 mm).(2)The main condensation period of soil condensation water in the study area is from 0:00 to 6:00,and the frequency of soil condensation water in autumn is the highest,followed by spring and summer,and the lowest frequency of soil condensation in winter.(3)The soil moisture content,air temperature,surface temperature,wind speed and relative humidity had significant effects on soil condensation water.The correlation coefficient between surface soil moisture content and condensation was the largest(r=-0.66)throughout the monitoring period,and the lower the moisture content,the higher the condensation amount.The effect of relative humidity on condensation water was greater at 4%-8% of surface soil moisture content,and the effect of relative humidity on soil surface condensation diminished as moisture content increased.At a surface soil moisture content was less than 14%,the condensation decreased with increasing surface temperature and air temperature,showing a significant negative correlation(P < 0.01).The effect of wind speed on soil condensation water in the study area showed that the breeze promoted condensation,which mainly occurred at night when the average wind speed was<0.2 m/s.(4)The magnitudes of condensation water observed in the same group for the openended,top-sealed and bottom-sealed treatments at 5,10 and 20 cm depths were openended > upper-sealed > lower-sealed treatment;as the soil depth increased,the start of condensation in the open-ended treatment was delayed,and condensation was more likely to occur in the soil at 5 cm depth.The contribution ratios of near-surface water vapor to soil pore water vapor were 0.28:1,0.37:1,and 0.81:1,respectively,indicating that soil condensation water vapor in the Loess hilly and gully region mainly originated from soil pore space.