That's what is so amazing about Langbeinite, the Sulfur in it is readily available in "Sulfate" form. Elemental Sulfur takes months to oxidize the Sulfur into SO4 (Sulfate), where as Gypsum and Langbeinite are both sulfates [CaSO4 and K2Mg2(SO4)3, respectively].
Even then, the sulfates themselves aren't what break apart CaCO3, but once the sulfates bind with the soil and come into contact with water, then the sulfates become sulfuric acid, which is what breaks CaCO3 apart. Citric acid works great in a pinch, but requires repeated applications because Citric acid doesn't bond to the substrate like Langbeinite or Gypsum will.
Gypsum can work instead of Langbeinite, but naturally the Ca in Gypsum could cause more harm than good. Omitting other Ca inputs from the soil would allow one to use Gypsum. However, I still highly prefer Langbeinite. My plants have been loving all the extra Mg and K, not to mention those 2 nutrients are often leeched from soils.
This article here explains things much better than I can. I'm going to include the most important excerpts from it, but I
highly recommend everyone read this article. Anyone having problems with seemingly unexplainable alkaline soils in their living soil should consider this and try Langbeinite.
"Results indicate that Na was leached from surface soils in all the treatments and the untreated control. Langbeinite most effectively enhanced movement of Na and caused initial increases in salinity that abated within 1 year. Gypsum enhanced movement of Na to lesser degree, and movement under S and compost was equivalent to untreated controls. Added compost did not affect activity of langbeinite, gypsum, or S"
"Elemental S is typically broadcast and incorporated with standard reclamation equipment in the fall at relatively low cost, making it practical for reclamation in arid regions. Elemental S is microbially oxidized to sulfate (SO4), which reacts with soil water to form sulfuric acid that solubizes Ca from CaCO3, which displaces exchangeable Na. While high concentrations of base cations, especially Ca, in the soil suggest that Ca-supplying amendments would not be effective, gypsum (CaSO4·2H2O) is commonly used to improve plant growth conditions in saline–sodic soils in reclamation settings. Gypsum is the most researched and available chemical soil amendment used to mitigate Na- affected soils, but has been criticized for low solubility and, as a result, low activity in arid region reclamation"
"When sufficient soil water is present to dissolve it, gypsum provides Ca to displace exchangeable Na and also SO4, which may cause some acidification and dissolution of existing CaCO3"
"Langbeinite (K2Mg2(SO4)3) is a potash mineral
that is roughly 130 times more soluble than gypsum"
"Researchers found that the high solubility of langbeinite resulted in improved soil structure (higher saturated hydraulic conductivity) compared with gypsum, but only exceeded the capacity of gypsum to reduce the sodium adsorption ratio (SAR) at the beginning of four-day column experiments.
Higher solubility suggests that it may more effectively displace exchangeable Na than gypsum under low and ephemeral soil water conditions."
"Results indicate that Na moved downward in all the treatments, including the control,
but that amendment with langbeinite more effectively mobilized Na (Fig.3)relative to initial soil properties (Table1). Both gypsum and langbeinite significantly reduced the ESP* (Fig.4), while elemental S did not affect Na mobilization compared with the untreated control.
Compost combined with the other amendments resulted in statistically identical concentrations as the amendments alone, and results from compost alone were equal to those of the untreated control, so only results from the three chemical amendments and untreated control are presented in Figs.3 and 4."
This part of the article points out Langbeinite's high K ratios (0-0-22), but it also emphasizes that all soils used in the study had similar K levels. The theory was that the soil and/or plants made full use of the high K from Langbeinite, as all 3 sample soils had similar K content. Quote below.
"
K levels were unaffected by the amendments, except for langbeinite, which contributed K. By the end of the study, however, K levels under
langbeinite in the upper two sampling depths were equivalent to those of the other, non-K-containing amendments"
This excerpt below points out a huge advantage of planting directly in the ground, as opposed to pots, as shown in the last sentence in the paragraph below.
"The typical agricultural approach for treating saline–sodic soils includes two steps (Havlin etal. 2011): first, mobilizing Na to improve soil hydraulic conductivity, and, second, leaching salts from the crop rooting depth. The first step involves chemical treatment by either: (1) applying amendments that contain cations with higher charge affinities for exchange sites than Na, such as Ca, Mg, K, or Fe; or (2) in calcareous soils with abundant Ca already present, applying acid-forming amendments such as elemental S to solubilize calcium carbonate (CaCO3) in the soil. In either case, Na is displaced on the cation exchange complex and the higher charge-density cations cause flocculation of soil particles and improved hydraulic conductivity. In the second step,
adequate irrigation water is applied to leach Na and other salts below the crop rooting depth"
So, proper watering with plants in the ground will result in many of the salts (Na, CaCO3, etc) being "pushed" down below the roots, resulting in zero negative effects. When in pots though? The salts have nowhere to go, so they often become concentrated at the bottoms of pots. This is especially true with fabric pots. Ever notice the scaling on your fabric pots after a few grows? This is why.
"Soils treated with langbeinite effectively leached more Na than other treatments, likely due to its rapid dissolution in water"
"Initial EC increases suggest that large amounts of Mg and K applied with langbeinite displaced Na on exchange and in solution, while the subsequent EC decline suggests that the Mg and K may have facilitated flocculation and leaching of the cations in solution."
"
Under langbeinite, reduced Na concentrations translate to decreased dispersion followed by enhanced movement of water and improved soil structure"
"As late spring snowmelt and small, early summer rain events evaporated in the high temperatures of June and July,
dissolved salts were transported upwards and precipitated when the system became dry, especially in the 3–8cm depth, causing slightly higher or equal concentrations of Na in July compared with April at all depths.
Evapo-concentration, or accumulated salts due to high evaporation rates, and a strong correlation between salinity and SAR in arid regions"
As stated above, when soil becomes too dry, there is too much evaporation of water, or both, the salts actually become more concentrated AND will move upwards into your root zone. The result? Alkaline pH and K and Mg being leached from the soil; not to mention the high pH and excess Ca also contributing to lockout. So, not only is there lockout, but leaching to boot!
If you've ever had random deficiencies or excess alkalinity with your pH, this is likely why.
tl;dr: Everyone should have Langbeinite on hand. A little goes a long ways and you'll find that it solves a lot more problems than you thought, and it will solve problems you didn't even know you had. I have no idea why more people aren't talking about Langbeinite. I'd love to see what living soil gurus say about Langbeinite, but I've found nothing but research articles like the one above.
All the best!
