The question
Name: ______________________ Date: ____________ Design an investigation of an agricultural practice and soil quality (10 points)
Model or diagram
Soil organic matter on a university research farm
A university research farm grows corn on flat fields that have the same soil type. For the last 12 years, some fields have been plowed every spring and others have been farmed with no-till (seeds planted directly into the residue of the last crop). A student notices that the no-till fields seem darker and crumblier. The farm's records for soil organic matter in the top 15 cm of soil are shown in the graph.
(a) Describe the difference in soil organic matter between the two practices shown in the graph after 12 years. Use numbers from the graph. [1 point]
(b) The student wants to test, with a controlled experiment, whether adding cover crops (plants such as rye grown over the winter and left on the field in spring) increases soil organic matter in no-till fields.
(i) Identify a testable hypothesis for the experiment.
(ii) Identify the independent variable.
(iii) Identify the dependent variable.
(iv) Describe an appropriate control group and its purpose. [4 points](c) Identify one variable that should be held constant in the experiment. [1 point]
(d) The student plans to use one field with a cover crop and one field without. Describe a change to the design that would make the results more reliable, and explain how it would help. [1 point]
(e) Explain why soil organic matter decreased in the plowed fields in the graph. [2 points]
(f) Describe one benefit to the farm of higher soil organic matter, and explain how it provides that benefit. [1 point]