Do plants grow better with microorganisms or without?

Question

for my science project i got 4 pots with soil. i micro waved 2 pots and left the other two for controls, i plants the same amount of seeds in each pot. i waterd them each day with the same amount of water for each pot. im at the end of my experiment but the results are weird i expected the two pots with microorganisms to grow the best but they are growing really bad and the two pots with all the micro organisms killed are growing really really well its strange. oh i also have to do a class presention and i have no idea what to say cause i know like nothing about microorganisms can any one help me out!!

Answer 1

I don't know what microorganisms you are talking about; but I do know that whatever they are, they have to eat.  They are probably living off of the nutrients in the soil that are meant for the plants.

Answer 2

Plants in native communities do have beneficial relationships with microorganisms known as plant mutualists. They can have mycorrhizal (myco = fungus & rhizo = root) symbionts as well as beneficial nitrogen fixing bacteria in the root zone, the rhizosphere. However your plants were not grown in established plant rhizosphere communities.

Were the pots used to grow plants before or were they new? If used they may have had accumulated salts or harbored dormant infective particles such as viruses or mold spores.

Look at this page for possible types of problems.

http://www.hcs.ohio-state.edu/mg/manual/...

http://hgic.clemson.edu/factsheets/hgic2...

http://www.ag.ndsu.edu/pubs/plantsci/lan...

http://www.nmmastergardeners.org/Pdf%20F...

Did you do anything different other than microwave the two pots that grew plants well? Did you wash, bleach or handle the pots differently in any other way that might have left a residue in the two non-microwaved pots? How did you mark or tag the pots to distinguish the microwaved from the other two?

Did the four pots get the same quality of light & humidity? Could the poor pair have been in a slightly hotter drier spot? Even if the four were in a line in a window did the healthy ones sit at one end and the poor pair at the other? Is there a gradient of growth down the line?

Did the soil come sterile or did you treat it also? If the soil was sterile and the pots new it is unlikely there was a pathogen introduced.

Did you feed the plants? How and what? Did they all get their water at the same temperature?

Are the non-microwaved potted plants diseased or lacking nutrients? To check take a hand lens and examine the plants for differences with the healthy plants. Look for insects, or discolorations. Look at leaf veins on both sides of the leaf.

Measure the length between nodes along the stem and leaf sizes. Compare these between the pairs. To get an exact size difference between plants it is typical to weigh each plant after washing the soil from the roots.

Collect the 4 soil samples separately and examine by eye and lens for differences.

Do a pH test on the four soil samples to see if the healthy pair had a better pH for growth. Get a soil test kit and distilled water to do the tests. For completeness get the  test kit for nutrients and pH. Do the tests twice on each sample to be sure your results are accurate and repeatable. (you could even practice on the garden soil before attempting your samples)

http://www.humeseeds.com/soiltest.htm

http://www.planetnatural.com/planetnatur...

Do a web search on pathogens specific to your plant species.  Also look up nutrient deficiencies for you plant species.

Sometimes results are just not as expected. If you carefully annotate your steps and review all your procedures for handling errors as well as look for any possible pathogen you will cover your bases.  Try to account for all possible variables the plants experienced and report your data.

Answer 3

The microorganisms in your soil were mostly ones that inhibit plant growth by competing for nutrients or causing diseases your plants. This is why plant growers start seeds or young plants off in sterile soil, they grow better.

It's true that many microorganisms are beneficial, such as mycorrhizae, which is a beneficial soil fungus.  These are added to plant soils by tablets or dips. This is because any soil that's been disturbed (or potting soil) is unlikely to have beneficial soil organisms - they die without their host plants. If you'd like to do an experiment on beneficial microorganisms, you would buy some mycorrhizal tablets (available in good garden shops) or liquid and add this to some of your plants.