I have an idea to throw out from a technical field fairly far from horticulture but sharing an interest in underground bacteria and their effects.

The bacterial degradation of certain organic compounds underground (the best studied are contaminants such as chlorinated solvents) can show whether the environment of the bacterial metabolism is aerobic (with free oxygen significantly available) or anaerobic (without). In systems that are overall aerobic and very facilitative of that condition (say deep sands) one often still sees traces of the anaerobic degradation pathway. So without knowing exactly what and where they are, one concludes that there exist microsites where oxygen can be depleted faster than it can diffuse inward.

So what is the possible implication to alkaline soils where we are concerned with pH (rather than Eh, being basically degree of oxygen availability)? Perhaps something as simple as wanting a coarser grain size of amendments or porous amendments. If I were to design a simple experiment I might apply ferrous sulfate to one plot (or pot) of alkaline soil showing iron deficiency in susceptible plants, apply (by mixing in) ground oak bark (slightly acidic and porous already, and will release acidity with decomposition) to a second plot, and for the third soak the same measure of oak bark in a solution of the same measure of ferrous sulfate and mix it into soil similarly. Then I'd plant and watch.

Or I'd just till into my alkaline garden a layer of ground oak or pine bark sprinkled with the ferrous sulfate solution to provide--one hopes--a favorable microsite of availability. Then I'd see if I got favorable results.

The horse manure I got for my roses had lime (calcium carbonate) and pH of over 8. Stables use lime to deodorize their stalls. Lime is a potent fungicide and I don't have any black spots nor botrytis on my roses - that I like. However, lime also raises pH, with phosphorus got tied up in calcium, and my roses' blooms decreased. Horse manure is high in phosphorus but the lime makes it unavailable.

My question is: does lime (calcium carbonate) moves with water, or does it stays where applied? Nitrogen moves withh water, but phosphorus and potassium stay put where applied (from EarthCo. booklet). Can I still keep the horse manure as mulch to prevent roses' fungal diseases, but use an ACID SOLUBLE fertilizer to break down the phosphorus in my fertile clay soil?

My garden pH of 7.7 give tons of blooms, except for roses. Alkaline clay soil is fertile with lots of phosphorus for plants thriving in the pH of 7.5 to 8.5 zone, such as Begonis, Callendula, Clemantis, Foxglove, Marigold, and Geraniums.

It's the picky roses that do best at pH 6.5 that I have to fix the soil. I need help with this: Is lime soluble and moves with water like nitrogen, or does it stay put where's applied like phosphorus and potassium? Many thanks for any info.

In most cases, calcium and magnesium are relatively stable - more so than potassium, in fact. This has to do with the strength of their (positive) charge and how strongly they attach to the (negative) charge of soil particles.

I am not sure how readily the complexed phosphorus is released once the carbonate is gone.

"Consider an iron sulfate drench if pH is not coming down below 6. If uptake of ammonium is not lowering media-pH quickly enough (a realistic target is 0.5 pH units within a week), a drench of iron sulfate (also called ferrous sulfate or FeSO4) can be applied to lower media-pH within a day or two. Iron sulfate can be purchased from agricultural suppliers.
Iron sulfate is moderately acidic and has the benefit of adding iron (20.8 percent by weight). The material is highly soluble at water pH below 6.0, and it can be applied as a drench at 2 pounds/100 gallons (2.4 g/L)."

Other info. given by the below link: "The recommended application rate for an iron drench is 5 ounces per 100 gallons of either Iron-EDDHA (several brands including Sprint 138 are available from many nursery suppliers), which provides 22.5 ppm iron, or Iron-DTPA (for example, Sprint 330), which provides 37.5 ppm iron). The letters EDDHA or DTPA are important because the iron form affects solubility at high pH (Figure 3). Iron forms decrease in solubility above pH 7 in the order from EDDHA (best) > DTPA > EDTA > sulfate (worst)."

That sounds confusing, so I'll order Neptune fish soluble fertilizer with Iron of 101 ppm.

"If your soil is not naturally acidic, mix in 1/2 to 3/4 peat moss with the planting soil. At the same time, mix in thoroughly 6oz. (12 teaspoons) of Ferrous Sulfate to a 3' x 3' area for each plant. If you want to change PH 6.5 to PH 5.5, apply 12 oz. In a 3' x 3' area around the plant and water well. Keep plants well watered"

My question: Can ferrous sulfate be mixed with vinegar (to lower my water at pH of 8 down to 6, where ferrous sulfate dissolves) - then use this solution to water rhododendrons and azaleas? Thank you in advance.

The above sounds good, but does iron sulfate need a pH of below 6 to be dissolved?

I'll look for ferrous sulfate as gonebananas suggested, dissolve this in water with some used lemon rinds, then water my 2 particular rhododendrons to see if that will fix the cholorosis (planted in EarthGro topsoil, pH of 8 - and I forgot to put in peat moss this year!)