Dynamic Characteristics and Drainage Assessment of Deep Soil Moisture in the Irrigated Farmland of Piedmont Region of North China Plain

In this paper,the observation equipment of deep soil water profile in the Luancheng ecological experiment station of Chinese Academy of Sciences was used to perform in-situ measurements of the soil water content in the depth of 15.4 m of soil profile for one continuous year based on the neutron moisture viewer.The deep soil and water samples were collected regularly,which were used to perform quantitative analysis of the variation of soil water content and deep drainage.The results showed that the distribution of soil moisture in the vertical profile is controled by the soil texture,and the variability of soil moisture decreases with the depth of soil.Meanwhile,the distribution of soil moisture was affected by the precipitation and irrigation within a year.Due to the effects of precipitation(irrigation) and evapotranspiration,dramatic variations of soil moisture occurred in the root zone.However,the response of soil moisture to the precipitation was delayed below the root zone.During the observation period,there was abundant water for the whole soil profile in the depth of 15.5 m and the soil water storage increased by 216 mm.However,the soil water content decreased in the wheat seasons and the soil water storage decreased by 208 mm.Estimated by the chloride mass balance method,the deep drainage was almost 65 mm in the depth of 560 cm of the soil profile.