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

Sprinkler irrigation alters soil hydraulic properties both at and below the soil surface, yet its effects are not well characterized. We evaluated the effects of sprinkler 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). The experimental design was a randomized complete block with two treatments (pre? and post?irrigation) and four replications. We used two half?circle spray heads to apply 127 mm of water at 70 mm h-1 in one irrigation to duplicate 1 × 2 m plots. Unconfined (three?dimensional) infiltration rates at steady?state were measured at potentials of -55, -35, and -15mm of water before and about 10 days after irrigation. Irrigation increased surface bulk density (0 to 34 mm) by 18% and increased the saturation ratio by 35%. At -15 mm, the unconfined infiltration rate was 53 mm h-1 before, but 16 mm h-1 after irrigation. At -35 and -55 mm, irrigation decreased infiltration by 68%. Irrigation also decreased infiltration nearly 5?fold through pores with diameters ranging from 0.55 to 0.86 mm. At each measured potential, irrigation tended to decrease hydraulic conductivity by 48%, on average. Sprinkler droplet impact consolidated unprotected soil and greatly reduced tension infiltration. Our findings provide useful input data regarding this and similar soils for models requiring hydraulic properties. In addition, our results provide valuable insight for managing infiltration and avoiding runoff during a growing season when surface properties change as recently tilled soils are sprinkler irrigated