Question
We have a garden plot that we added quite a bit of horse manure too. The soil tests we've done show low nitrogen. The plants are stunted for the most part. Some have yellowing leaves. Corn seems to be doing better than some of the others, and the melons are slightly suffering. The tomatoes seem to be suffering the worst.
We have attempted to fertilize with nitrogen. Can this remedy our problem for this planting or is it likely that the stunted plants will never recover.
I'm anxious to do whatever I can if it might save my garden.
Thanks,
Lisa

Answer
Classic case of Too Much of a Good Thing!  Nevertheless, and I hate to say it, your first move MUST be: GET A SOIL TEST!

Visual observation is all you have to work with until your soil test results are back.  As you have already figured, the Stunted Growth and Yellowed Leaves have almost certainly been caused by your Manure overdosing.  A soil test will give you the evidence -- confirming what we are educatedly guessing, introducing precise data for the kind of ratios and amendments you need to correct your particular soil.  Much depends on the CEC numbers -- your soil's 'Cation Exchange Capacity'.  This is the shortcut you want.  This is going to solve your problem perfectly.  Tell me where you live, and I'll tell you where to get a modestly priced soil test quickly.

I think you probably realize that this is a VERY complicated problem -- most likely involving multiple toxicities, some of those inducing deficiencies in other nutrients that are actually present but unavailable for uptake.  A high Phosphorous level is bad, but actual Phosphorous toxicity is unusual.  High Phosphorus levels as you suggest may be inhibiting uptake of Nitrogen; the N deficiency presents as weak, pale, small leaves and slow, stunted growth.  But we know that many other deficiencies can take the blame for stunting a plant's growth.

Corn is actually considered a reliable indicator of mineral deficiency -- an H2PO4 deficiency causes a buildup of a pigment called Anthocyanin, which accumulates when a plant is stressed, streaking leaves in purplish red.  Excess Phosphorous will cause deficiencies in other nutrients -- Zinc, Copper, Iron; these plants look chlorotic, and have weak stalks and poor seed development.  You point out that your Corn is faring relatively well -- better than some of your other crops.  Plants grown with excess Nitrogen exhibit a dark green color and excessive leaf growth; buds and fruit.  If you are going to correct a micronutrient devicience, make sure it is SPRAYED onto the leaves, since the soil chemistry may tie up micronutrients.
Vegetables and Flowers vary dramatically in sensitivity to mineral shortages, and react differently, it is very hard to really know EXACTLY what is wrong with your soil.  It has got to be measured.  You need a soil test.

The University of Arizona Cooperative Extension website posts relevant report titled 'Diagnosing Plant Damage: Key to symptoms of chemical disorders on individual plants'.  Some of its points:  'Potassium, Zinc or Copper excess can inhibit uptake of Iron.'  Symptoms include 'stunted new growth with interveinal chlorosis: young leaves are very small ('little leaf'), sometimes missing leaf blades altogether, and internodes are short giving a rosette appearance.'

On Phosphorous they state: 'Plants may take up the Phosphate anion in luxury amounts.'  You can read the entire report online:

http://ag.arizona.edu/pubs/garden/mg/damage/key.html

University of Montana posts a report, 'Plant Nutrient Functions and Deficiency and Toxicity Symptoms' that will help you assess your situation:

http://www.montana.edu/wwwpb/pubs/mt44499.pdf

Note that the ideal soil pH for Phosphorus utility lies between 6.5  and  7.5.  Did that Manure alter the pH significantly?  I can guess it did -- but how much?  if any?

Horse Manure is the Gold Standard when it comes to amendments.  And most soil could use plenty of Manure, because most soil is desperately low in Phosphorous.  A lot of processes -- Photosynthesis included -- depend on P4 to get out of bed in the morning.  Manure is a Phosphorous Superpower, concentrating things like Molybendum, Copper, Manganese and Zinc into a potent dose that can quickly become excessive.  Just ask someone who tries to grow a Lawn around new construction on real estate that used to be a farm -- the pH is so low it's practically in China, and the stratospheric Phosphorous levels are landing on the Moon.  But it doesn't have to be Quantity to be a problem.  What was the Quality of this Manure?  How aged was this Manure you applied?  How much tilling in did you do to incorporate this into your soil?  Was this soil used for ANYTHING else before it became yours, perhaps recently?  And what kind of Manure was it?

Veins, green with color loss between veins -  Iron, manganese, magnesium, molybdenum deficiencies or fungus, virus, insects, mites, low temperatures, toxic materials in air or soil, excessive water, copper, manganese or zinc

There are many ways to treat these problems.  If the pH is off, you can pretty much figure that NO correction is possible until you fix that -- and you must get that soil test for that..  Add no nutrients until this problem is solved.

Colorado State University meanwhile posts advice titled 'The use of manures as soil amendments and contain salts and may increase the soil salt level when used as mulch or soil amendments. mulches for vegetables & ornamental plants' by Curtis Swift.  First line: 'Manures This elevated salt level can be a serious problem when the resulting soil salt level is greater than the salt tolerance of the plant. This is likely to occur when the soil is already on the border line of salt tolerance of the plants being grown.'  Vegetables can also suffer from excessive Salt levels; amending them with high-salt Manure would lead to other problems.

http://www.coopext.colostate.edu/TRA/PLANTS/index.html#http://www.colostate.edu/...

Many cautious authorities will recommend against applying ANY Manure to a Vegetable Garden.  Concern about E. coli and other pathogens leaves them cautious.  Even 'treated' Manure comes with no guarantees, they point out.  It's something to consider.

I would love to give you the simple answer you are looking for.  This is however a complicated problem, ONLY because we do not really know what the problem is!  And I have tried to simplify the whole situation while conveying that it could be something that adding Nitrogen will exacerbate.  Don't lift a finger here.  Get your soil tested and get up close and personal with your closely held real estate.  Now, what is your County/State or Zipcode?  It will tell you where that perfect soil test is.