Author
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Lehrsch, Gary |
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KINCAID, DENNIS - USDA-ARS (RETIRED) |
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Submitted to: Soil Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 2/10/2006 Publication Date: 6/1/2006 Citation: Lehrsch, G.A., Kincaid, D.C. 2006. Sprinkler droplet energy effects on soil penetration resistance and aggregate stability and size distribution. Soil Science. 171(6):435-447. Interpretive Summary: Water droplets thrown from center-pivot irrigation systems can strike unprotected soil surfaces with such force or energy that they break naturally occurring clusters of soil called aggregates. When aggregates are broken, their fragments are carried by water entering openings or pores at the soil surface, often obstructing those pores and forming about a 3-mm thick, dense layer of surface soil. After the irrigation ends, this layer of soil dries to form a difficult-to-penetrate crust that frequently hinders or prevents the emergence of seedlings of many small-seeded crops, especially sugarbeet. We conducted this study to see if, by modifying sprinkler irrigation systems to reduce droplet energy, we might reduce crusting and thereby increase emergence. From 1997 to 2001, we evaluated the effects of a low, medium, and high rate of sprinkler droplet kinetic energy on surface penetration resistance (PR, a measure of crust strength), aggregate stability (a measure of an aggregate’s ability to resist breakdown), and the size distribution of water-stable aggregates. Each year near Kimberly, ID, we planted sugarbeet into a tilled field of Portneuf silt loam, then irrigated 2 to 4 times. We applied 17 mm of water at the season’s first irrigation, or 14 mm at each subsequent irrigation, using a lateral-move sprinkler system (very similar to a center-pivot system) with irrigation spray heads having either smooth or spinning deflector plates. After the first and last irrigation each year, we measured PR and collected soil samples at the surface (0 to 6 mm) to determine aggregate properties. When measured after one irrigation, surface PR increased and aggregate stability generally decreased as droplet energy increased, although the magnitude of the response differed from year to year. When measured after multiple irrigations, PR decreased linearly with increasing droplet energy, likely due to erosion of the crusted surface. We also found that water droplet energy altered aggregate size distributions by breaking the larger aggregates to form smaller ones. Analysis of data from 1998 through 2001 revealed that droplet energies about 25% greater than our medium rate were most damaging to surface soil. Producers should modify their irrigation systems so that they produce water droplets with no more than moderate amounts of kinetic energy to minimize damage to surface soil. Technical Abstract: Sprinkler droplet energy (DE) degrades surface soil structure, often leading to surface sealing and crusting. Modifying sprinkler irrigation systems to reduce droplet energy may reduce soil 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 per kg 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 2 to 4 times. We applied 17 mm of water at the season’s first irrigation, or 14 mm at each subsequent irrigation, 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) for determining aggregate stability and size distribution via wet sieving. When measured after one irrigation, surface PR increased and aggregate stability generally decreased as droplet energy increased, although the magnitude of the response differed from year to year. When measured 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 per kg or more. Trend analysis of soils data from 1998 through 2001 revealed that DEs is greater than or equal to 10.6 J per kg decreased MWD most. Producers should reduce sprinkler droplet kinetic energy to less than 10.6 J per kg to minimize surface structural breakdown of recently tilled soil. |
