EPPWS 311/511 Leaching Experiment

The movement of herbicides in soils is determined by three factors:

1. The attraction between herbicide molecules and soil colloids (clay and organic matter).

2. The water solubility of the herbicide.

3. The amount of water which passes through the soil.

Herbicides differ from one another in their leaching characteristics within the same soil. Also, the same herbicide will have different leaching characteristics in different types of soil. This exercise will demonstrate the movement of herbicides in soils. We will use five different herbicides in two different soils. We will work in groups, with each group using a different herbicide and soil.

READ INSTRUCTIONS 1-9 BEFORE YOU START

1. Select one column of sandy soil or one of loamy soil (see your groups soils assignment).

2. Select the herbicide solution assigned to your group. The concentration of each herbicide is 1000 ppm.

3. Shake the herbicide solution to mix. Remove 5 ml herbicide solution using a 1 ml pipet , and apply the solution evenly over the soil surface of each column.

4. Cover the soil surface with a thin layer of untreated soil and lay a filter paper over the surface.

5. Slowly add water to the top of the column (125 ml for the sand column and 225 ml for the loam). After all of the water is added, keep the column upright for at least five minutes.

6. Push the bottom of styrofoam cups tightly into the top of the columns and secure with duct tape.

7. Turn the column on its side and carefully remove the tape covering the slit. Mark the depth of water penetration by placing a piece of tape on the body of the column.

8. Dig about 1 inch of soil out of the slit to form a small trench, and plant plenty of grain sorghum in the exposed soil. Cover the seed with a layer of untreated soil.

9. Using tape, mark each column to indicate which end was the top, what herbicide was used, and what soil type is in the column. Write on the tape, not the column. Place the columns together on the designated bench in the greenhouse.

We will return to the farm in two weeks to observe the results.