Question
QUESTION: I am wintering in Florida.  Being an Illinois farmer I have a question concerning manganese (Mn) and magnesium (Mg).  Can you explain the basic differences?  Here in south Florida with sandy soils nutrients have to be added.  Epson salt is a good form of Mg, right?  What can I use for Mn?  Thanks

ANSWER: Magnesium (Mg) is one of the 3 憇econdary?elements plants need to be healthy.  A single Mg ion lies at the center of a huge molecule of Chlorophyll; remove the Mg, and you no longer have Chlorophyll.  To give you an idea, the Chlorophyll molecule is a VERY close match to something called Hemin, the pigment that makes our blood Red.  One basic difference between Chlorophyll and Hemin is that Chlorophyll contains Mg; Hemin contains Iron (Fe) instead.  There may be only on molecule of Magnesium in Chlorophyll.  But if the Mg isn't there, it isn't Chlorophyll.

When it comes to Manganese (Mn), Plants need A LOT LESS of it.  Mn is only a trace element -- and since you asked, you'll find it in generous amounts in Brown Sugar, Blueberries, Wine and Chocolate, among other things.  It's actually fairly common.

Now, although Mn is not part of the Chlorophyll molecule, Mn ions are CRITICAL for the Chlorophyll molecule to work.  Without Magnesium, Photosynthesis can't take place.  Deprived of Magnesium ions, no Green plant is able to transfer light-stimulated electrons OUT of Water molecules to make Energy.  Your plants may as well be growing in the dark.  Give them all the Sunlight you want; if Magnesium is missing, Green plants are helpless.

OK, we know you need Mg for Photosynthesis.  What if you give your plants EXTRA Magnesium?

In 1986, researchers at Univ. of Florida in Gainesville tested the 'Effects of lime and applied Mn on plant Mn, growth and chlorophyll concentration of Tifway II Bermudagrass'.  Essentially, they fertilized Tifway II Grass with additional Magnesium to see if they could get the Grass to make more Chlorophyll.  And they found it made no difference.  It would be nice, but it just doesn't work that way.

You can read the full text here:

http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=6943701

Now let's get to the rest of your question.  You're basically figuring that if your Soil is low in Mg or Mn, you can just add it, and you抣l have healthy plants.  Let's assume you actually tested for this, and you're not just adding a whole shopping cart of minerals to fill the refrigerator.  Avoid starvation by feeding your crops everything, right?

Not so fast, my friend.

It's true that sandy Soil -- if you can actually call it 'Soil' -- has very little of anything you can call nutrients.  That's fairly obvious.  You can't grow much of anything in Sand without outside help.

Unfortunately, that's not the problem in Florida.

Even if you DO add these elements, and others, you still haven抰 solved one of the other major problems of Florida Soil: It is highly Calcareous.  Which means it is packed with freely available Calcium and Magnesium Carbonates.  Which makes it IMPOSSIBLE for some of your OTHER favorite vitamins and minerals to be absorbed by roots.

Never be fooled into thinking that farming in Florida is as simple as adding a shopping list of missing nutrients.  

Soil in the Florida sits on a bed of Calcium Carbonate deposits (CaCO3) -- Seashells left behind by marine life over millions of years.  The Carbonates in light, White, Florida soil cause it to be STRONGLY alkaline.  The pH is almost always higher than 7.2, and sometimes it's closer to 7.4.  Calcium and Nitrates are abundantly available to any plant you put in these Soils, which may seem nice.  Trouble is, there's too much of it.

Phosphorus, Iron and Manganese may ALSO be there in your Florida Soil.  But they are all chemically locked out of the roots of any Plant you want to grow in them.  They are absolutely, positively UN-available to your crops.  A plant simply can't get to them.  No matter how much of them you have, your plants show symptoms of deficiencies.

In some parts of the world, Calcareous soils are Black.  TTo us, they look like rich, fertile silt.  Yet farmers there deal constantly with terrific shortages of nutrients.  TOO MUCH Copper, Iron, Zinc, Phosphate or Calcium in a plot, and Manganese becomes completely locked out of plant roots.  That's what you have in Florida.

This is why, when Citrus growers fertilize, they have to approach it differently from the way you would in Illinois.  The high pH and the Calcareous base dictate whether or not all the vitamins and minerals in the Soil are ever going to be delivered to their Orange and Lime groves.  This explains why Chlorosis is such a common problem in Florida soils.

What's a snowbirding farmer to do?

Organic Matter, sir, is the BEST treatment for your sandy Soil.  You'll fix all kinds of problems easily and efficiently.  Way better than eternally dosing it up with endless doses of Epsom Salts or anything else.  Compost, Humus, Leaf Mould, Manure -- these are the keys to building available Soil nutrients.  Because although Biochemistry can be really complicated, just managing your Soil right will make it possible to grow anything your heart desires, my friend.  ANYTHING.

Have a quick glance at 'Citrus Fertilizer Management on Calcareous Soils' by Thomas Obreza, Ashok Alva and David Calvert at the Extension Service/University of Florida website:

http://edis.ifas.ufl.edu/BODY_CH086

They note, 'It is often difficult to increase leaf Mg and K levels with fertilizer applied directly to Calcareous Soils, which contain tremendous quantities of both exchangeable and nonexchangeable Ca...High Ca levels suppress Mg and K uptake by Citrus trees in part, presumably, through the competition of Ca2+, Mg2+ and K+.'

See those 'plus' signs?  That's positively charged Atoms!  Citrus growing on soils high in Ca usually needs EXTRA Mg and K fertilizer.  'The only means of increasing leaf Mg or K concentration may be through foliar application of water-soluble fertilizers, such as Magnesium Nitrate [Mg(NO3)2] or Potassium Nitrate (KNO3).'

They also point out, 'Soil pH is the most important factor regulating Zn and Mn supply in alkaline soils.  At alkaline (high) pH values, Zn and Mn form precipitous compounds with low water solubility, markedly decreasing their availability to plants.  A soil pH value of less than 7 is preferred to ensure that Zn and Mn are available to plants in sufficient amounts.  The soil around a plant root (the rhizosphere) tends to be acidic due to root exudation of H+ ions.  Therefore, soils that are slightly alkaline may not necessarily be deficient in Zn or Mn.  In addition, Zn and Mn can be chelated by natural organic compounds in the soil, a process that aids the movement of these nutrients to the plant root. On highly alkaline soils, however, Zn and Mn deficiencies are not uncommon.'

And my favorite statement: 'Soil applications of Zn and Mn fertilizers are GENERALLY INEFFECTIVE in these situations.'

See that?

They point out that Zinc and Manganese supplements are used commonly in the form of ZnSO4, MnSO4, ZnO and MnO fertilizers.  But they warn, 'Broadcast application of these compounds to correct Zn or Mn deficiencies in calcareous soils is not recommended, since the Alkaline pH renders the Zn and Mn unavailable almost immediately.'

Chelated Zinc, they note, 'is sometimes, but not always, superior to inorganic Zn sources. Soil applications of chelated Zn are rarely economical... Manganese Chelates have limited effectiveness in Calcareous soils and are not normally used.'

The most economical way to build up levels of Zn and Mn is with foliar spraying.

One last point.  You haven't mentioned your snowbird location.  Depending on where you are in Florida, Nematodes may create overwhelming micronutrient deficiencies in some crops.  Looks like we抮e not in Illinois anymore, Roger.

Sorry if this a little technical; I've tried to simplify (which can take a lot of time, as you surely noticed).  Your followup(s) invited.  Thanks for writing.  Send oranges.

---------- FOLLOW-UP ----------

QUESTION: Thanks for your answer.  Where I put down cow manure... 2 years ago... my Queen Palm tree is outstanding, with lush green fronds.  Since then I put down 50 bags of cow manure last March. Now nearly everything in my small yard is looking good.  Is there any negatives to applying cow manure to this Florida sand and we have some clay (this is in a motorhome resort) which came from digging lakes in are resort.  By the way we are in Hendry County 17 miles east of Ft. Myers. We want to apply 160 pounds ( 4 bags) of cow manure per Royal Palm.  Does that make sense?

Answer
'Manure' as an amendment is one of the richest sources of organic matter you can put on the table -- slow-release N-P-K, micronutrients, soil structure enhancements and other components of great soil.

How much, exactly, varies.  Not just by Manure.  Not just by Cow.  But by the day.  The same Cow will supply varying values of minerals and other qualities, depending on what that Cow ate for breakfast.

Cow Manure in general boasts around a 6-2-5 N-P-K ratio.  Remember, this is Organic food.  It's not supposed to force-feed your crops, or in this case your Palms.  Manure and other Organic fertilizers rev up when the soil is hot, and slow down when it's cooler.  It self-adjusts perfectly to pace the metabolism of everything growing in it.  Because as you know, plants grow faster when it's hot and slower when it's cold.  The best that man-made fertilizer can do is to slow release at a constant rate for a long period of time.  And the stuff it releases doesn't come close to matching the complex molecules that float onto the table.  It's like the difference between the Sun rising vs you and me turning on the light switch when we enter a room.  These rates evolved slowly over millions of years.  No Scotts product can come close except in their ads.

OK, you're growing Queen Palms.  University of Florida issues advice on the care and feeding of Palms, and the pro's there specify that you should find a 4-1-6-2 fertilizer (Nitrogen, Phosphorous, Potassium and Magnesium).  Larger Palms respond to a 4-1-6-2 Mg (N-P205-K20-Mg) formula.

The Univ of Florida folks also point out something you should know:  Palms are VERY susceptible to nutrient deficiency.

If you don't know that yet, you may be finding it out soon.

So it will be wise if you read those fertilizer labels and make absolutely sure that any fertilizer you use on them contain 1 to 2 percent Iron and Manganese and traces of Zinc, Copper and Boron to avoid deficiencies.

But do you NEED that much Manure?  Remember, variety is the spice of life.  Why not read 'Improving Soil Structure' at the Arizona Cooperative Extension website to expand your options:

http://ag.arizona.edu/pubs/garden/mg/soils/improving.html

Cover Crops (aka 'Green Manure') and Compost yield improvements in your Sandy Soil without OD'ing on Phosphorus, Salts and other goodies you get with Manure.

Finally, the best thing you can do is to get yourself a Soil Test.  Scientists take their lab equipment and analyze your Soil; then they tell you whether or not you need that Manure, and precisely how much, if any.  Soil tests are not expensive -- one test will cost you less than a tank of gas.  Let me know if you need the contact details for this and I'll be happy to post it for you.  After I finish shoveling some of this Snow.  On second thought, maybe I oughta drop this shovel right here and buy myself a plane ticket...