My Soil Test shows a Lot of Calcium…. So, Why Do I Need to Buy It?

Written by:  Jim Miller – Sales Manager – Aqua Aid, Inc. & Verde-Cal Products

May 2015

It’s very common, in many regions, to see a soil test that shows Calcium Base Saturation at levels adequate or even excessive.  60 – 70 percent base saturation of calcium is adequate for a balanced level of this very vital and important nutrient.

Many times a soil test shows imbalance of important cations (Mg, K, Na, H) due to an imbalance of the calcium.  Because Calcium is very dominant, it can sort of “rule the roost” when it comes to all the other cation’s finding space within the soil structure.  Many times the imbalance or excessive amounts of calcium are caused by improperly amending the soil profile.  And believe it or not… utilizing calcium as an amendment will help keep calcium levels from becoming excessive.

How does this imbalance happen?  If your soil test shows excessive calcium it is most commonly due to the fact that your soil is made up of particles that are derived from Calcium Carbonate and sometimes even Calcium Phosphate or calcium silicate.  Regardless of the source, they are carbonate based sources.  Calcium carbonate is very abundant in the Earth’s crust.  When we use this commonly found soil, whether it be sand or loam, the calcium carbonate will eventually end up becoming dominant unless there is adequate amending from time to time with other calcium sources.  It is this carbonate form that causes excessive calcium levels.  Switching to another calcium source is the best option to begin changing or reversing this effect.

Other calcium sources being primarily calcium sulfate.  The popularity of calcium sulfate over the past ten years proves that the source is doing something different or better as an amendment.   Because a carbonate form of calcium has a very strong “affinity” to the soil colloid, the use of a sulfate form of calcium has the exact opposite effect.  There is no affinity of calcium sulfate to the soil colloid and therefore this source will not raise calcium (or pH)  on its own.  In fact the sulfur and calcium repel and basically treat the three most important needs in the soil and plant.  These three being:  feeding the plant, leaching and interaction with the soil colloid are the exact effect of calcium sulfate all while eliminating the risk of raising Calcium levels.   When you utilize a very available source such as Verde-Cal G, you will actually see a turf response due to the very available calcium and sulfate.

Is my Calcium unavailable?  Here is a statement that is “over-used” in our industry.  Next time you are told that a nutrient is tied up, ask the person: “how is that possible”?  And see if they have an answer.

The answer can be due to many factors.  Tied up Calcium could be due to the source of calcium as mentioned above.  It could be due to high sodium or magnesium.  It could be due to heavy or tight soils, it could be due to poor water quality of the irrigation source, it could be due to the fact that no calcium is being applied.  A lack of aeration of the soil can also lead to poor availability on nutrients.

The only true way to know if your calcium is tied up is to run a Saturated Paste Test.  This test will show you exactly what is available of the calcium that you actually have in the soil root zone or the portion of the root zone that you soil tested.  In turf, it is extremely common to see Saturated Paste Tests that show very un-available calcium as well as other important cations.  In fact, I would venture to say that of the tests that I see, 90 out of 100 show unavailable nutrients.  This may be the answer as to why you are being told to buy more calcium!  But, first read on…

Why are these tests so lop-sided?  It goes directly back to soil amending.  For nutrients to function, release and work, there needs to be more nutrient added than presently being applied.  Remember, if your nutrients show extremely low availability, then what you are doing is not working!  So change it, or better yet, start looking at what you’re spending and buying as compared to the expectations you desire.   Why are you taking the soil/paste tests?  Because you obviously care about what you are doing to improve the soil structure and ultimately the plant.

The plant diet.   Most times there is simply too little calcium being applied and with the wrong source and this leads to un-availability of that calcium.  What little calcium availability there was, has been taken up or leached or exchanged with the soil colloid and there is none left.

Adding more will help change this, of course.

What the professors say.   Many Universities are telling you to cut back on calcium applications when the soil test shows an excess.  Those same soil tests may show high potash, but the University will not tell you to cut back on potash.  This makes no sense.  And now we see improved turf and transition recovery in the spring when calcium was applied in the fall.  Many times these same Universities that tell you to stop using calcium are also telling you to use it in the fall because it will help strengthen the plant.

Any turf manager that hangs his/her career on the line every day basically know that the addition of calcium is way too important to simply over look.  But these same turf managers may be using the wrong source of calcium for their specific region.

Just like other nutrients, calcium has numerous sources!  All nutrients can be derived from different sources.  All these sources have advantages and disadvantages.  Calcium is no different, but Calcium often gets overlooked!

In areas of high calcium base saturation, calcium sulfate is the choice.  As mentioned earlier in this article, this source works far better in high calcium soils.  Get to know the different sources and what they can do for you.   Calcium carbonate is very insoluble and requires high rates to be effective.  Calcium levels are raised with calcium carbonate.   Anyone who has ever lifted a bag of calcium phosphate knows that you are dealing with a very in-soluble product.  Calcium phosphate is very dense and very heavy and basically a very insoluble grain of sand in a bag.  Calcium silicate has been the hot ticket item for about 12 years.  Born in South Florida in the sugar cane market, it has migrated into the turf market.  Calcium silicate however brings a high risk of raising calcium levels even higher while providing a marginal amount of silica.  The risk is not worth it.

Most other forms of calcium are spray-able and will not provide enough calcium per acre in the soil to benefit the soil structure.

This leads us back to calcium sulfate, or, Verde-Cal G.  Still the best option for high calcium soils.

Verde-Cal G provides all the benefits and advantages of a great calcium source without affecting the already present calcium levels.

Those that use Verde-Cal G will typically realize a turf response within a couple of days.  This is due to the lack of “affinity” to the soil colloid.  The calcium is left to do its job in the soil.


Now you know how to answer the question:  Why is my calcium tied up and un-available to the soil and plant.  And now you have a better alternative to feeding the proper source and diet of calcium to your properties.  Remember to look at the labels and check for the sources of calcium in the products you are using.  Especially if your calcium is already too high.