|LI, YI - Northwest Agricultural & Forestry University|
|REN, XIN - Northwest Agricultural & Forestry University|
|HILL, ROBERT - University Of Maryland|
|Malone, Robert - Rob|
|ZHAO, YING - Northwest Agricultural & Forestry University|
|HE, JIANQIANG - Northwest Agricultural & Forestry University|
|REN, TUSHENG - Northwest Agricultural & Forestry University|
Submitted to: Pedosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/17/2016
Publication Date: N/A
Interpretive Summary: Water repellent soils are generally formed through organic substances coating the soil particles from processes such as burning or fungal growth. Research on the infiltration characteristics of water repellent soils have been been conducted, but information regarding water infiltration at different levels of water repellency at different positions in a soil profile is limited. The objectives were to measure the infiltration characteristics of a Lou silt loam soil obtained near Yangling, China, at four levels of water repellency and positioned at either the depth increment 0-5 cm (scenario I) or 5-10 cm (scenario II) in a laboratory soil columns. The levels of water repellency were wettable and slightly, strongly, and severely water repellent soils. The infiltration rate initially decreased with time (called stage 1) until it leveled off to a constant value (called stage 2). During stage 2 infiltration, the average infiltration rate (AIR) decreased with increasing soil water repellency. The AIR decreased at approximately the same rate with increasing water repellency for both soil depth scenarios (I and II). The overall infiltration rate decreased dramatically with increasing water repellency level. For example, the times required for 10 cm of cumulative infiltration with the four increasing levels of water repellency were 6.2, 64.8, 971.0, and 1667.5 hours. The results suggest that the water infiltration rate decreased with increasing water repellency and that the depth position of the water repellent layer was less important than the level of water repellency. This research will help soil scientists more fully understand water infiltration in water repellent soils and potentially lead to improved agricultural management practices with these soils.
Technical Abstract: Hydrophobic soil can influence soil water infiltration, but information regarding the impacts of different levels of hydrophobicity within a layered soil profile is limited. An infiltration study was conducted to determine the effects of different levels of hydrophobicity and the position of the hydrophobic layer on cumulative infiltration, infiltration rate, wetting front movement and water content in the soil profile. Lou soil was treated with octadecylamine to produce a wettable, slightly, strongly, or severely hydrophobic 5-cm soil layer positioned either at the soil surface and overlaying a 5-cm sand layer (scenario I) or covered by a 5-cm sand layer (scenario II). As the hydrophobicity level of the Lou soil layer increased, the cumulative infiltration (CI) decreased, being 1.77, 1.17, 0.68, 0.38 cm at 10 min in scenario I and 11.9, 3.29, 1.39, 0.70 cm at 540 min in scenario II. The time (t) for a given amount of CI increased with the increasing hydrophobicity level of Lou soil layer, being 370, 3890, 58260, 100050 min at CI of 10cm for scenario I and 80, 1950, 11430, 56100 min at CI of 4 cm for scenario II. Infiltration rates (i) deceased non-linearly with time and varied with the hydrophobic level of Lou soil layer. Severely hydrophobic soils exhibited slow infiltration rates for both scenarios I and II. Depths of 5-cm in scenario I and 10-cm in scenario II were found to be division depths of infiltration stages. The i-t relationship produced good fit when using Kostiakov equation (R2>0.72) in the 1st infiltration stage. Average infiltration rate (AIR) were used for describing the infiltration behavior in the 2nd stage, which also decreased with the increasing hydrophobic level of Lou soil layer, being 0.126, 0.021, 0.002, 0.001 mm min-1 for scenario I and 0.112, 0.003, 0.002 and 0.0005 mm min-1 for scenario II. The AIR decreased at approximately the same rate with increasing hydrophobicity for both scenarios. The wetting fronts advanced more slowly as the hydrophobicity level of the Lou soil layer increased and resulted in non-linear variations of wetting front movement versus time for all treatments. The Lou soil layer produced sharp transition zones of soil water content and water content decreased as hydrophobicity level of the Lou soil layer increased at any given depth. The position of the hydrophobic soil layer was generally of secondary importance compared to the hydrophobicity of the soil layer in affecting infiltration behavior and properties.