Sprinkler droplet energy effects on soil penetration resistance and aggregate stability and size distribution

Sprinkler droplet energy degrades surface soil structure. Modifying sprinkler irrigation systems to reduce droplet energy may reduce surface sealing and crusting, thereby increasing emergence. From 1997 to 2001, we evaluated the effects of sprinkler droplet kinetic energies of 0, 8, and 16 J kg(-1) on in situ surface penetration resistance (PR, a measure of crust strength), aggregate stability (a measure of a soil's resistance to breakdown), and water-stable aggregate size distribution, expressed as a mean weight diameter (MWD). Each year near Kimberly, ID, we planted sugarbeet (Beta vulgaris L.) into an initially tilled field of structurally weak Portneuf silt loam (Durinodic Xeric Haplocalcid), then irrigated two to four times using a lateral-move sprinkler system with spray heads having either smooth or spinning, four-groove deflector plates. After the first and last irrigation each year, we measured PR in situ and collected soil samples at the surface, 0 to 6 mm. When measured after one irrigation, PR increased, and aggregate stability generally decreased as droplet energy increased, although the magnitude of the response differed from year to year. After multiple irrigations, PR decreased linearly with increasing droplet energy, likely due to erosion of the crusted surface. Five-year average MWD after multiple irrigations decreased by 10%, to 0.42 mm, with droplet energies of 8 J kg(-1) or more. Trend analysis of soils data from 1998 to 2001 revealed that droplet energies >= 10.6 J kg(-1) decreased MWD most. Producers should reduce sprinkler droplet kinetic energy to < 10.6 J kg(-1) to minimize surface structural breakdown of recently tilled soil.