Passage V

Manure mixed with water, known as a slurry, is spread on top of a soil to provide additional plant nutrients. The slurry covering alters how rain erodes the ground surface. A study was done on a particular soil with and without slurry on top to determine the amount of runoff (water and sediment that runs off the surface) and the concentration of sediment in the runoff during a simulated rainfall event.

Study

A volume of the soil was completely dried and then passed through a screen having 9.5 mm diameter openings to remove larger particles. A 25 cm deep layer of the dried, screened soil was placed in each of 2 flumes (shallow, flat-bottomed trays) that were 2.5 m long, 1.0 m wide, and 0.3 m deep (see Figure 1). The flumes had a 5% slope. The dried soil in both flumes had a bulk density of 1,400 kg/m³. Bulk density includes any air or water present in the spaces between the soil particles.

The entire surface of the soil in one of the flumes was then covered with slurry. Once completely dry, it formed a 1 cm thick layer on top of the soil. Next, a sprinkler 2 m above each flume delivered rainfall at a rate of 80 mm/hr for 45 min, after which it was turned off. Over each 5 min of rainfall, all the runoff from the soil was collected from the trough using the runoff drain. For the collected runoff from each 5 min period, the runoff volume, in L, and the concentration of sediment in the runoff, in g/L, was determined. Figure 2 and Figure 3 show the runoff volumes and sediment concentrations, respectively, for each period.