Sprinkler Irrigation Effects on Infiltration and Near-Surface Unsaturated Hydraulic Conductivity

Authors: Lehrsch, Gary; KINCAID, D - USDA-ARS (RETIRED)

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/8/2010
Publication Date: 4/27/2010
Citation: Lehrsch, G.A., Kincaid, D.C. 2010. Sprinkler Irrigation Effects on Infiltration and Near-Surface Unsaturated Hydraulic Conductivity. Transactions of the ASABE. 53(2):397-404.

Interpretive Summary: Soil organic carbon (SOC) from dairy manure can help to restore the productivity of and crop yields on eroded soil. SOC, irrigation, or both may alter soil water flow (hydraulic) properties. We evaluated effects of SOC and simulated center-pivot irrigation on infiltration and near-surface, unsaturated water flow in a structurally unstable, recently roller-harrowed Portneuf silt loam. Main plot treatments were pre- or post-irrigation and subplot treatments were SOC contents, 3.5, 8.0, or 9.5 g/kg. We applied 127 mm of water at 70 mm/h in one irrigation to duplicate 1 x 2 m plots using two half-circle spray heads 6 m apart, each with a spinning, 6-groove deflector plate located 3 m above the soil. Three-dimensional infiltration rates were measured at three tensions in very wet, nearly saturated soil before and about 10 days after irrigation. Infiltration rates were used to calculate unsaturated soil water flow rates at each tension. Irrigation, but not SOC, affected soil physical and hydraulic properties. Irrigation increased surface bulk density by 16% and increased the soil=s saturation ratio (a measure of soil water content) by 30% following the measurement of infiltration 10 days after irrigating. At the lowest tension (e.g., in the wettest soil), the infiltration rate was 49 mm/h before, but 15 mm/h after irrigation. At greater tensions (e.g., in slightly drier soil), irrigation decreased infiltration by two-thirds. Irrigation decreased infiltration 10-fold through surface pores with diameters ranging from 0.75 to 1.5 mm. Sprinkler droplet impact consolidated the soil and greatly reduced tension infiltration.

Technical Abstract: Soil organic carbon (SOC) from dairy manure can help to restore productivity of eroded soil. SOC, irrigation, or both may alter soil hydraulic properties. We evaluated effects of SOC and simulated center-pivot irrigation on infiltration and near-surface hydraulic conductivity (K) measured under tension in a poorly structured, recently roller-harrowed Portneuf silt loam, Durinodic Xeric Haplocalcid. Main plot treatments were pre- or post-irrigation and subplot treatments were SOC contents, 3.5, 8.0, or 9.5 g/kg. We applied 127 mm of water at 70 mm h-1 in one irrigation to duplicate 1 x 2 m plots using two half-circle spray heads 6 m apart, each with a spinning, 6-groove deflector plate located 3 m above the soil. Unconfined (three-dimensional) infiltration rates were measured at potentials of -60, -40, then -20 mm of water before and about 10 days after irrigation. Steady-state infiltration rates were used to calculate unsaturated hydraulic conductivities at each potential. Irrigation, but not SOC, affected soil physical and hydraulic properties. Irrigation increased surface bulk density by 16% and increased the soil=s saturation ratio by 30% following the measurement of tension infiltration 10 days after irrigating. At -20 mm, the steady-state infiltration rate was 49 mm/h before, but 15 mm/h after irrigation. At -40 and -60 mm, irrigation decreased infiltration by two-thirds. Irrigation decreased infiltration 10-fold through surface pores with diameters ranging from 0.75 to 1.5 mm. Sprinkler droplet impact consolidated the soil and greatly reduced tension infiltration.