Growing Legumes with
'Fertilizer Factory' Nodules

Now that you know the secret of legumes symbiosis, let's see it in action.

Note: For this activity we suggest using a small seeded legume like clover,
so you see a result sooner.

Meet Harlan

You will need:

• 12 legume seeds (these must not be cooked or roasted!)
• Matching rhizobia inoculum (packed in peat, available from stockfeeders and seed merchants)
• 6 black plastic pots or 6 cups (make sure to put drainage holes in the bottom)
• Sand for filling your 6 pots (you can get sand from any garden center) - use builders sand or beach sand for best results. Do not use soil because it may already contain rhizobia.
• Popsticks for labelling your pots
• Waterproof texta
• Water

In this activity, you will grow half of your legume seeds without rhizobia and half inoculated with rhizobia. Rhizobia are much too small to see, but there are thousands of them in the peat inoculum. In order for this activity to work, you will have to be very careful that there is no contamination by these tiny rhizobia. Follow the instructions carefully and as your plants grow you will see how these tiny little bacteria perform miracles. They 'fix' nitrogen from the air and provide it to the legume roots.

Getting set up

1. Get your six pots. (If you use cups, make sure there are holes punched in the bottom to provide drainage.)
2. Put enough gravel in the bottom of the pot to cover the drainage holes, then fill the pot with sand to within 1-2 cm of the top.
3. Gently but firmly tap the soil down and water the pot thoroughly (until water drains through the drainage holes).
4. Label your popsticks: 3 should be labelled: "with rhizobia"; 3 should be labelled: "no rhizobia"
5. Put one popstick in each pot and separate them into 2 groups (1 group is 'with rhizobia' and one group is 'no rhizobia').

Planting your 'no rhizobia' pots

It is best to do these pots first. If you did the 'with rhizobia' pots first, you might accidentally contaminate the 'no rhizobia' pots with peat inoculum that might be on your hands or spilt on benches etc.

• Make 2 holes in each pot with the 'no rhizobia' labels.
• Add one seed to each hole.
• Gently press soil down over the seed.
• Add a little water and set these pots aside to make sure they don't get contaminated.

Planting your 'with rhizobia' pots

Remember to keep these pots separate from the others.
The drainage water can contaminate your 'no rhizobia' pots.

• Make 2 holes in each pot with the 'with rhizobia' labels.
• Add one seed and a pinch of peat inoculum (which contains thousands of rhizobia) to each hole.
• Gently press soil down over the seed.
• Add a little water.

Growing your plants

1. Put your pots someplace sunny without the chance of getting blown over (like a sunny windowsill, the back patio or best of all - a glasshouse!)
2. Keep the 2 sets of pots apart to prevent contamination. There are thousands of rhizobia bacteria in each speck of peat and you don't want any to get into your 'no rhizobia' pots.
3. Keep your pots moist - you may have to add water once - twice - thrice a week! Keep checking.
4. Watch the plants grow and record your observations in a book. Record things like:
   • Which day did you plant your seeds?
   • Which day did the plants emerge?

Comparing your plants

• Can you tell a difference between the 2 sets of plants? (Hint: nitrogen-deficient plants are small and yellow compared to plants getting enough nitrogen.)
• After the plants have been growing for 4 weeks, pull up two plants from a with rhizobia pot and two from a no rhizobia pot. Keep track of which plants came from the with rhizobia pot (it's a good idea to keep the popstick with the plants.)
• Shake the sand out and gently rinse the roots with water. (Don't do this in your sink or you will clog up the drain and your parents will be annoyed!)
• Sketch the two root systems. Do they look different? Do some roots have bumps on them? What are these bumps called?
• Cut one of the 'bumps' in half (with a knife or pinch it open with your fingernail). Is it pink inside?

Keeping your plants going

• If you decide to keep some of your plants, you can plant them in the garden or keep watering them in the pots.
• If you keep your plants in the pots, add some fertiliser, but remember - they don't need nitrogen like other plants because the rhizobia are fixing it for them!