The question
Name: ______________________ Date: ____________ Soil texture and erosion on a test slope (10 points)
Model or diagram
Pilot results: soil washed off three soil trays
(a) A class wants to know how soil texture affects how much soil is washed away by heavy rain. They fill three identical trays with soil (sandy soil, loam and silt loam), each 5 cm deep, and tilt every tray to the same 15° slope. A watering can with a sprinkler head pours 2 L of water on each tray over 2 minutes, and the class collects the muddy water that runs off the bottom, dries it and weighs the soil. A pilot run with one tray of each soil gave the results in the graph. Identify the independent variable in this investigation. [1 point]
(b) Identify the dependent variable in this investigation. [1 point]
(c) Write a testable hypothesis that matches the pilot results. [1 point]
(d) Identify one variable the class kept constant, and explain why keeping it constant matters. [2 points]
(e) The pilot run used one tray of each soil. Describe one change to the design that would make the results more reliable. [1 point]
(f) The class repeats the test on the loam, but this time they tilt the trays to 30° instead of 15°. Predict how the mass of soil washed off will change, and explain your prediction. [2 points]
(g) A farmer's field has the same silt loam as the class's silt loam tray and sits on a slope beside a stream. Describe one environmental effect on the stream of the soil loss shown in the graph, and explain how the soil loss causes it. [2 points]