results from other experiments may be similar to or quite different
from classroom findings. Given the variability in biochar and soil
properties, it is likely that classroom findings will differ from findings of other experiments. Results in Figure 10 were taken from
published field, greenhouse, and laboratory experiments to show
variability in responses of plant growth (A and B) and soil respiration (C and D) to biochar addition. These previous experiments
have shown positive, negative, and neutral results of biochar soil
amendment, depending on the soil type and the biochar properties. One reason for this variability is soil pH (Appendix 1).
Differences in pH between biochar and control treatments and
soil types may help explain differences in plant growth and soil
respiration. For example, biochar has a large effect on corn yield
in an acidic soil (Figure 10A), whereas biochar has no measurable
effect on corn yield in a basic soil (Figure 10B). Students can measure soil pH and visualize differences between treatments by
graphing dot charts (Appendix 1).
Comparing classroom experimental designs and results with
previous experiments gives context to the students’ work and
allows for meaningful discussion about the nature of scientific
investigation. For example, our classroom soil respiration experiment was conducted over a 24-hour period, while the laboratory
(Figure 10C) and greenhouse (Figure 10D) soil respiration experiments were conducted over 50 days and 10 weeks, respectively.
Ask your students why the soil respiration results over 10 weeks
differ from those of their 24-hour experiment. In this case, the
classroom experimental design resulted in a CO2 concentration
that reached the maximum detectable limit in the compost treatments (Figure 9), whereas the garden-soil CO2 concentrations
continued to increase, similar to the results in Figure 10. Use
these results as an opportunity for students to objectively critique
the experimental design and suggest ways to improve it, rather
than criticizing themselves for “doing it wrong.” Teachers and students can refer to Figure 10 to discuss variability in experimental
results and show that scientific experiments rarely come to one
“right” answer or conclusion. Using the CER framework, task students to use multiple pieces of experimental evidence from classroom experiments and other experiments to develop a scientific
argument (Appendix 2).
The plant growth and soil respiration experiments align with
NGSS and the CER framework to engage students in an authentic
science experience. Students will develop soil and plant disciplinary knowledge and gain experience with science practices.
Together, students will craft a scientific argument using data generated both by their class and by professional scientists. This integrated approach connects students to ongoing, relevant research
in soil and plant science.
This work was funded by the U.S. Department of Agriculture
National Institute of Food and Agriculture Research Initiative–
Coordinated Agricultural Projects Bioenergy Alliance Network of
the Rockies grant no. 2013-68005-21298.
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