Question
QUESTION: I am a analytical chemist that is interested in making a soil micronutrient solution that will make my citrus trees more healthy. The leaves are slightly yellow which makes me think iron deficiency.I have access to Hampene Fe a iron chelate. I also found that 0.9 w/w Chelated Fe is what some propietary products use. If I make that solution how much do I use per tree or do I need to dilute it further. Is it harmful to use by itself or do I use it with other micronutrients.

ANSWER: HOOOOOOOOOOLD THE PHONE!  You need a Soil Test first.  Right?

Odds are, you'll find there's PLENTY of Iron in your Soil.  As a chemist, you may know that Iron deficiency -- Chlorosis -- strikes when Soil is the wrong pH.  Of course, it could be just plain poor.

Sure, if it's Sandy, your Soil won't have enough Iron for your Oranges, Limes, whatever.

But it's much more likely that you've got a pH block that keeps Iron from getting into those roots.  Because Soil pH, not nutrients, determines whether those nutrients can be absorbed.

In a perfect world, your Acid Soil loving Citrus trees grow best in Soil with a pH 6 to 7.  Entire regions test in the 6 to 7 pH range with no problem.  But push the pH above 7, and you are suddenly dealing with life threatening shortages of Zinc, Manganese, Iron and other important nutrients that become virtually nonexistent to all things Citrus, while other plants are flexing their Iron-rich muscles wondering what all the fuss is about.

Fixing Soil pH is not easy.  Calcareous (Limestone) Soil, like you find in Florida, may be to blame for symptoms of Iron, Manganese and Zinc, which can all show up together in the same Tree.  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.

If you have a poor-Soil problem, you won't fix it at all by adjusting the Soil pH.  If Soil pH and Iron numbers are good, but Leaves are Chloritic, you could be looking at a problem with the Roots.  In the end, it boils down to what the Soil analysis finds and recommends.

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:

edis.ifas.ufl.edu/BODY_CH086

The researchers 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.  Slight Yellow leaves may turn bright Green if you did that.

Tell me where you live and I'll refer you to the Cooperative Extension in your area that will do a first rate Soil test.  Then we can talk about your other options.  Thanks for writing,

THE LONG ISLAND GARDENER






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

QUESTION: OK! Here goes!I took a sample of soil around the citrus tree and measured the pH in my pH meter at work. The pH was 9.1.
Even I was amazed the tree is still alive. What do I do next?

Answer
I'm speechless.  Nine Point One.  This is a tree you should donate to the Smithsonian.  I didn't know real Soil could get that basic.

Even microbes can't stand to live in pure lime.  Calcareous Soil is almost always the case when you have a pH above 8.0, and it's VERY hard to correct it.  In that situation, you can't really do anything until all the Calcium Carbonate is dissolved.

However, in an EXTREME case such as this, where you are dealing with SODIC Soil, you would not expect high Calcium Carbonate levels.  Calcium Sulfate -- Gypsum -- can be helpful; apply Gypsum, then irrigate the hell out of it to leach out all the Salt.  This may also improve Soil structure while bringing high Sodium levels down to Earth and making nutrients more available in the process.

I don't know how quickly the pH will come down, but you don't want to cause any problems by over-pushing this and damaging the Citrus roots -- too much of a good thing is never a good idea.  But make some headway.  While you're handling this, see if some applications of Iron might help your plant.

Gentle doses of Nitrogen applied in the form of Ammonium Sulfate (NH4NO3; 21-0-0) will point your Soil in the right direction.  Get the pH down to 7.3 and you will be getting some missing nutrients from Soil microbes.  Amend your Soil with Peat Moss, a highly acidic material that will lower your pH, and pine needles if you have any access.  This should be done over a period of time.  It would also not hurt to boost your microbial Fungus populations, which further helps to lower the pH and make several other corrections as well.

L.I.G.