Passage V

Soil sealing occurs when rain breaks exposed soil particles into smaller pieces, which then fill empty spaces in the soil. This process decreases the rate at which water infiltrates (soaks into) the soil. Three studies investigated factors affecting soil sealing.

Study 1

Samples from the top 5 cm of 2 different soils (A and B) were analyzed for their relative proportion of sand, silt, and clay. The results are shown in Table 1.

Srudy 2

Dried samples of each of the 2 soils were placed in separate trays that had perforated bottoms. The trays were put into shallow water to saturate each soil and then were allowed to drain. The trays were then placed on a 5% slope and subjected to simulated rain from a fall height (distance from the rain source to the tray) of 0.4 m at a constant rate of 40 mm/hr (see Figure 1) . The runoff (amount of water that ran off the soil's surface) was measured for each tray every 6 minutes for 2 hours. The amount of rain that infiltrated each soil during each 6-minute period was calculated by subtracting runoff from rainfall.

This procedure was repeated twice, using simulated rain from 2 other fall heights. Each repeat used fresh samples of both soils prepared as described above. The calculated infiltration rates for each 6-minute period are shown in Figure 2 for Soil A and Figure 3 for Soil B.

Srudy 3

The impact velocity and kinetic energy per kg of rain for the simulated rain falling from the 3 heights used in Study 2 were calculated. The results are shown in Table 2.

Tables and figures adapted from I. Betzalel et al., "Water Drop Energy and Soil Seal Properties." @1995 by Williams and Wilkins.