Compaction, Aging, and Raindrop‐Impact Effects on Hydraulic Properties of Saline and Sodic Vertisols

Vertisols markedly swell and disperse when wet because of the high percentage of montmorillonite in the soil. We hypothesized that soil bulk compaction, time since soil wetting (aging), and raindrop impact affect seal formation, soil permeability, and salt leaching of Vertisols. Vertisol (Typic Chromoxererts) samples with exchangeable Na percentages (ESP) of 0.4 and 11.8 were subjected to simulated rainfall of deionized (DW) and saline (SW) (electrical conductivity [EC] = 5 dSm ‐1 ) waters with 0 and 18.1 J mm ‐1 m ‐2 impact energies. In a Vertisol without aging (0.5 h of prewetting) and under zero compaction, subjected to DW and SW rainfall, seal formation controls the soil permeability. Under DW rainfall, the final infiltration rates (FIR) of the sealed and unsealed Vertisol samples were 6 and >44 mm h ‐1 at ESP 0.4, and 5 and 17 mm h ‐1 , respectively. Four days of aging without compaction, followed by DW rainfall, increased the FIR of unsealed soil to 37 and to >44 mm h ‐1 at high and low ESP, respectively, and that of sealed soil to 12 and 14 mm h ‐1 at high and low ESP, respectively. Subjecting wet soil to pressure up to 800 kg m ‐2 decreased the unsealed Vertisol FIR under DW rainfall to 8.9 and 27 mm h ‐1 at high and low ESP, respectively. Seal formation and bulk compaction had little effect on salt leaching in the low‐ESP soil. Under bulk compaction or seal formation, the high‐ESP soil leachate EC decreased from 10.7 to 9.0 dS m ‐1 after 300 mm of DW rain.