Science Buddies: "Ask an Expert"

Hello,

We are really interested in trying the nitrogen fixation experiment where we would grow clover with and without nitrogen added (either fertilizer or Rhizobium spp.). However... we only have about 3.5 weeks until the science fair and the procedure indicates that we should wait 5-6 weeks for the plants to fully mature before testing the soil.

I'm wondering if we will we see significant results at that point or if the plants really need to be fully mature (5-6 weeks indicated in the procedure) for the differences in [N, P, K)] in soil to be resolved by a rapid test kit.

BTW I am in Canada and am looking at using the 'Luster Leaf 1601 Rapitest Soil Test Kit' rather than the kit specified in the project materials section, since is readily available here (and a bit cheaper).

Alternatively is there another plant species we could use that might show results within 3-4 weeks? I expect clover was chosen particularly for its short growing time, but its worth asking.

Also, I'm wondering if root nodules will be visible in our time-frame (3-4 weeks). We could always attempt the soil nutrient measurements, but if the differences aren't yet significant we could just present the biomass data along with visual observation of nodules (and other health indicators in the plants like colour, etc).

Thanks in advance to anyone who can share there experience with this project - much appreciated!

Hi lkadlec!!

This is a really cool hands-on project on nitrogen fixation. I assume that you are referring to this Science Buddies project: "Bacteria Can Fix It! A Comparison of Nitrogen-Fixing Bacteria and Nitrogen Fertilizers." Nitrogen fixation is easier to see in plants in the legume family. This is normally seen as beans, but actually includes plants like clover, alfalfa, and fava bean. Past experiments relating to nitrogen fixation have been used on these plants. While the optimum time for growth is 5-6 weeks as stated in the experiment, I do believe that you should get quantifiable results by day 24. While you would have less data, I think that the conclusions you would reach would be similar to those you would reach by 6 weeks. I would also like to note that many times, seeds are already precoated with rhizobium. In this case, it is important to ensure that the seeds you purchase for this experiment are not.

As you would expect, the presence of root modules has a lot to do with the plant you would be using. On alfalfa plants, it takes around 4 weeks. Root nodules become present at the flowering stage of a plant, so it would be best to find a legume with the shortest time until the flowering stage. However, in most plants, this stage occurs after 35 days. This means you might not be able to see the root nodules in the time frame. However, you could attempt to speed up germination by soaking the seeds in water for an hour before sowing it. My recommendation would be to conduct this experiment on multiple species of leguminous plants in the hope that one of then is able to produce root nodules by the time of harvest. I hope this helps and your experiment is successful! Let me know if you have any additional questions/comments.

Thanks, Probiotics