Re: Would the zinc in soil be attracted to a magnet planted in the soil?

Complete question:

I did a science fair project and now that I think of it, my conclusion may not 
be correct. I planted some plants and planted anmagnet directly under the seed 
of half of them. I observed and recorded the growth and discovered that the 
magnet tray's plants grew more numerously, faster, and developed faster(I 
tested spring peas, bush green snapbeans, and lima beans and none of the lima 
beans grew). My conclusion was that the magnets attracted minerals that help 
the plants grow like zinc was a major one that they needed. I also placed a 
magnet in the soil and washed it off and patted it dry to see if there were 
minerals attracted to magnets in the soil and there were some particles in many 
forms still attached to the magnets: orange metallicy, small pebbles with 
sparkles, ans even one in the form of a small hair. Was my conclusion correct, 
partially correct, or incorrect? Am I on the right track? Do you have any 
advice? Thanks! 

Reply:

To be able to draw conclusions from your experiment, I would need a detailed 
description of your experiment and your data. Did you have replication (more 
than one plant per treatment)? Were your data subjected to statistical analysis 
that showed a statistically significant effect? How did you measure plant 
growth? Height is not a very accurate measure of plant growth although widely 
used. How much light did your plants receive? Did all the plants receive the 
same environmental conditions except for the magnet? Did the plants without a 
magnet contain lower levels of zinc or other mineral nutrients than the plants 
with a magnet?
 
I think your hypothesis is doubtful because a plant's roots permeate the soil 
very thoroughly in their search for mineral nutrients. Therefore, a magnet 
under the seed would not seem to offer a benefit, even if it could attract some 
minerals. Plants absorb most mineral nutrients in the form of ions from the 
soil solution. Most of these ions would not be attracted to a magnet. As you 
observed, various soil minerals fragments will adhere to a magnet if it is 
placed in soil. However, the range of a magnet is at most a few mm, so it 
cannot attract them from a great distance nor "pull" them to itself because 
other particles are in the way.