LEGUMES & THE NITROGEN CYCLE

We LOVE science! We LOVE plants! We LOVE microbes!

The third graders learn about life cycles in their classroom, so we taught them about the nitrogen cycle in the garden! We focused on how special plants called legumes are able to trap and harness atmospheric nitrogen in little Rhizobia-filled nodules in their roots that we call “pink pearl pockets.” The students observed a whole fava bean plant closely and drew it in their journals.

We broke off parts of the root system full of nodules for each student to look at under a hand lens.

These hand lenses allow the students to observe the roots at 10x magnification and see the fantastic intricacies of the nodules. Wow!

Once they had finished drawing, we asked them to pop the nodules and look inside. “Ooh looks like blood!” was a common observation. These nodules are actually full of a compound called leghemoglobin, which is similar to the hemoglobin found in our blood! I was very, very thrilled to see the students observing & making that connection on their own!

After the students learned all about the nitrogen cycle and how plants are able to restore the soil with root nodules, they learned about the importance of green manure in sustainable gardening practices. We walked over to a patch of fava beans we had planted in the winter, chopped them all down, and turned them into the soil. Ah, the nitrogen cycle at work!

It’s incredible to see how receptive students are to experiential learning. They heard about the abstract idea of nitrogen cycling through the ecosystem and then directly got to involve themselves in that cycle by interacting face-to-face with the stars of the show, the fava beans. Before we even explained what we were doing with the favas, a light bulb went off in one of the students’ heads and he said, “Oh I get it! We are returning nutrients to the soil!” Moments like this are so, so rewarding because it shows that we are able to lay a platform on knowledge onto which students can make their own conclusions and predictions about the natural world!