Drop Impact Energy‐Soil Exchangeable Sodium Percentage Interactions in Seal Formation

Abstract

AbstractConstant intensity rain (40 mm h−1) with 3.2‐mm drops falling from 0.25‐, 0.90‐, and 2.63‐m heights and impact energies of 1.8, 7.6, and 18.6 kJ m−3, respectively, was used to produce seals on two soils in 55‐mm deep by 82‐mm diam acrylic cylinders. Soil exchangeable sodium percentage (ESP) was altered to ESP 0 (Casaturated soil), 5, and 10 before rain was applied. Infiltration rate (IR) and hydraulic conductivity (HC) of A horizon material from the Wyman (fine loamy, mixed, thermic Typic Haploxeralfs) and Wyo (fine loamy, mixed, thermic Mollic Haploxeralfs) soils decreased due to formation of soil seals as raindrop energy and ESP increased. The Wyo was more susceptible to sealing than Wyman despite its higher organic C content because of its higher (17 vs. 9%) clay content. Seal formation on Ca‐soils (ESP 0) increased gradually with increasing drop impact energy. Soils with ESP 5 and 10 were more susceptible to sealing at low energy rain than were ESP 0 soils. Relative HC and final IR (FIR) decreased with increasing ESP with all rainfall energies and with the no rain treatment on both soils. Aggregate dispersion by raindrop impact and chemical dispersion by sodicity are two complementary processes leading to seal formation. A 5‐Mg‐ha−1 phosphogypsum treatment applied to the Wyman surface reduced seal formation and maintained HC and FIR near the unrained‐on values for the 1.8 and 7.6 kJ m−3 treatments. The 18.6 kJ m−3 raindrop energy produced a seal on the gypsum treated soil with relative HC and FIR more than four times as high as the untreated Wyman.