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plant nutrient deficiency experiment

David R. Hershey dh321 at PGSTUMAIL.PG.CC.MD.US
Fri Feb 23 01:12:32 EST 1996

Possibly the problem is too high a concentration of nutrient solution. I
often use half-strength Hoagland solution especially for young seedlings
that have received only plain water to germinate them. Molybdenum toxicity is
another possibility because molybdenum trioxide has molybdenum in a
different form than in the 85% molybdic acid recommended for Hoagland

I doubt if the problem is a pH decline if you actually had a Hoagland
solution because Hoagland solution number one has all nitrogen as nitrate
which almost always cause nutrient solution pH to rise. Even Hoagland
solution number two has only 7% of N as ammonium so should not cause a
major pH drop. Checking the nutrient solution pH is always a good idea 
and can be a good experiment. The houseplant, Heartleaf philodendron, causes
the pH of Hoagland solution number one to drop to below 4 all the time, 
whereas virtually all other species cause pH to rise above 7. Many 
species will cause the pH of an iron deficient solution to decrease.

Another good tool for solution culture work is an electrical conductivity 
meter, which gives an indication of the solution concentration. Pocket EC 
meters sell for $50 or so.

Exactly what is the recipe that was used? There are a lot of Hoagland 
solution recipes in print, but few are the original Hoagland solution. 
Most substitute an iron chelate for the iron tartrate Hoagland used, 
which is desirable, but some may make other changes.

I agree that pure solution culture is preferable to perlite culture. I 
give directions for constructing hydroponic equipment from plastic soda 
bottles in my 1995 book, Plant Biology Science Projects (Wiley, NY). 
Request copies of my several hydroponic teaching articles (via U.S. 
mail) from Elaine Johnson at ej7 at umail.umd.edu

Rather than tomato seedlings, I prefer rosette or vine houseplants 
because they can be rooted directly in solution. My favorite is piggyback 
plant (Tolmiea menziesii) which forms adventitious plantlets on its 
leaves. The plantlets are easily rooted. It is fun to look at its root 
caps under the microscope because they are dark red.

David R. Hershey
Snail mail: 6700 Belcrest Road #112, Hyattsville, MD 20782-1398

Adjunct Professor, Biology/Horticulture Department
Prince George's Community College, Largo, MD 20772-2199

Email: dh321 at pgstumail.pg.cc.md.us

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