Rain impact soil crust. III. Effects of continuous and flawed crusts on infiltration, and the ability of plant covers to maintain crustal flaws

Abstract

Experiments on unsteady infiltration, through rain-impact soil crusts on an albaqualf, employed 70 mm diameter cylinders surrounded by airsplash-exchange areas. Significant throttling effects resulted. Circular, fabricated flaws of varying diameter caused strong bypassing of the crust by infiltrating water. As the percentage of total area flawed rose from 1% to 10%, infiltration rates rose from near those of fully-crusted values to those of uncrusted values, further areal increases bringing little change. This result suggested three-dimensional water movement beneath flaws. Sheltering by plant covers produced flaws in the rain-impact soil crust. However, sheltered areas often acted as traps for incoming, finely comminuted, airsplash debris which, once deposited, could also throttle infiltration. Moreover, the compacted layer, the main throttling agent of the rain-impact soil crust, often extended laterally into sheltered areas. Wheat-straw stems, less than a drop diameter apart, were effective flaw preservers, even under heavy airsplash, inhibiting formation of the compacted layer and stimulating removal of airsplash deposits. Grass covers, dense enough to intercept all raindrops, were also highly effective against infiltration throttling because intercepted raindrops were converted, via the double-edge effect, into non-erosive, fine, impact droplets which could not disturb the soil.