Pedosphere 28(5): 775--792, 2018
ISSN 1002-0160/CN 32-1315/P
©2018 Soil Science Society of China
Published by Elsevier B.V. and Science Press
Characteristics of Water Infiltration in Layered Water-Repellent Soils
LI Yi1,2, REN Xin1, Robert HILL3, Robert MALONE4, and ZHAO Ying5
1College of Water Resources and Architecture Engineering, Northwest A & F University, Yangling 712100(China)
2Key Laboratory of Agricultural Soil and Water Engineering in Arid and Semiarid Areas, Ministry of Education, Northwest A & F University, Yangling 712100(China)
3Department of Environmental Science and Technology, University of Maryland, College Park MD 20742(USA)
4USDA-ARS, National Laboratory for Agriculture and the Environment, Ames IA 50011(USA)
5Key Laboratory of Plant Nutrition and the Agri-environment in Northwest China, Ministry of Agriculture, Northwest A & F University, Yangling 712100(China)
      Water-repellent (WR) soil greatly influences infiltration behavior. This research determined the impacts of WR levels of silt loam soil layer during infiltration. Three column scenarios were utilized, including homogeneous wettable silt loam or sand, silt loam over sand (silt loam/sand), and sand over silt loam (sand/silt loam). A 5-cm thick silt loam soil layer was placed either at the soil surface or 5 cm below the soil surface. The silt loam soil used had been treated to produce different WR levels, wettable, slightly WR, strongly WR, and severely WR. As the WR level increased from wettable to severely WR, the cumulative infiltration decreased. Traditional wetting front-related equations did not adequately describe the infiltration rate and time relationships for layered WR soils. The Kostiakov equation provided a good fit for the first infiltration stage. Average infiltration rates for wettable, slightly WR, strongly WR, and severely WR during the 2nd infiltration stage were 0.126, 0.021, 0.002, and 0.001 mm min-1 for the silt loam/sand scenario, respectively, and 0.112, 0.003, 0.002, and 0.000 5 mm min-1 for the sand/silt loam scenario, respectively. Pseudo-saturation phenomena occurred when visually examining the wetting fronts and from the apparent changes in water content (△θAP) at the slightly WR, strongly WR, and severely WR levels for the silt loam/sand scenario. Much larger △θAP values indicated the possible existence of finger flow. Delayed water penetration into the surface soil for the strongly WR level in the silt loam/sand scenario suggested negative water heads with infiltration times longer than 10 min. The silt loam/sand soil layers produced sharp transition zones of water content. The WR level of the silt loam soil layer had greater effects on infiltration than the layer position in the column.
Key Words:  infiltration model,layered soils,ponded infiltration experiment,pseudo-saturation soil water content,soil water movement,soil water repellency,water drop penetration time
Citation: Li Y, Ren X, Hill R, Malone R, Zhao Y. 2018. Characteristics of water infiltration in layered water-repellent soils. Pedosphere. 28(5):775-792.
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