For years, conventional fertility recommendations have advocated lime as a means of correcting soil acidity. But almost never did we hear of calcium's critical role as an essential nutrient. Sometimes your soil may need calcium even though soil pH appears within an optimum range.
We tested the pH of pure sand and found it neutral. But it contained no plant-soluble calcium. Taking a soil pH to decide whether you need calcium is like checking the oil in your pickup to see if it's out of gas.
When we see a disappointing crop yield in renewable farming programs, a low level of available calcium is almost always involved. However, plants can't respond to calcium if other yield limiting factors stand in the way. Things such as nitrogen deficiency, phosphorus shortage, insect disease, or drought can affect response to calcium. But the common denominator of poor yields in renewable farming programs lies in low-soluble calcium levels in the soil.
We often recommend reducing or dropping potassium chloride (KCL or muriate of potash) and anhydrous ammonia from a fertility program. When they're gone, we know we've eliminated two very aggressive calcium extraction agents. One reagent used to extract calcium from soil in a soil test is an extract solution of potassium chloride.
There’s substantial data showing that less than 1% of the potassium in KCL becomes available to plants in the year it's applied. What's happening with the large quantity of potassium chloride in conventional fertilizer programs is that it is splitting nutrients, particularly calcium from the clay and organic complex.
Anhydrous ammonia raises the pH very high at the site of injection. Typical soil pH leaps to 8 or 10 at the anhydrous injection site shortly after it's applied. Later in the season, the same soil usually drops lower in pH than the surrounding area as free calcium is depleted.
Soil pH doesn't reveal the crop's need for calcium
I want to particularly stress the difference between soil pH and soil calcium. The pH scale is a measure of hydrogen ion concentration; it runs from 0 to 14: Zero is most acid, 7 neutral and 14 is most alkaline. The scale is logarithmic; one-point change of pH means a 10-fold change in hydrogen ion count; a two- point change in pH is a 100-fold change in hydrogen ions.
We've drawn soil samples from the same location in a field each week for the entire growing season, and find that pH varies considerably. We've seen pH go from 6.5 in mid-May to 4.9 in mid-July. Yet most lime recommendations are based on a pH test taken at just one point in the season, usually when no crops are growing.
We've also discovered that when wet soil dries out, pH falls markedly, meaning the soil is more acid.
Soil becomes naturally more acid in much of the upper Midwest for several reasons. Soil organisms and plant roots exhale carbon dioxide. When this reacts with water in the soil, it forms a weak carbonic acid. Soil microbes also release organic acids.
Nitrogen fertilizers like anhydrous ammonia or ammonium sulfate cause soil to become more acid. Livestock manure’s also cause soil to become more acid.
Many crops grow well through a moderate range of pH, as long as they receive adequate and balanced nutrients. However, in field conditions it's difficult to provide balanced nutrients in an acid or alkaline soil. Some nutrients such as nitrogen, phosphorous, potassium, sulfur, calcium and magnesium become deficient at a pH of 5.5 and lower. Alkaline conditions - a pH of 7.5 to 8 - can cause iron, manganese and boron deficiencies.
One of the really exciting reasons to work toward a soil that's biologically alive is that soil organisms do a very good job of buffering and correcting soil pH. At low pH, bacteria and actinomycetes cannot flourish. But fungi can, and fungi tend to raise soil pH. If a soil is high in pH, fungi don't multiply much but bacteria and the actinomycetes do - and they’ll add acids which buffer the soil back toward neutral.
Also, earthworms help adjust soil pH toward neutral. Their castings are always closer to neutral than the parent soil they ingest.
A current college level soils text notes that only 1% of crop and pastureland in the U.S. has an optimum amount of calcium. It adds that as of 1980, farmers were adding only 18% of the calcium required to maintain proper calcium levels.
I've observed over several years that the higher the organic matter in a mineral soil, the greater the plant's tolerance for a lower pH. That emphasizes the extreme importance of good calcium levels if your soil is lower in organic matter.
We're generally more concerned about calcium in the east and southeast United States, which have higher annual precipitation that leaches out calcium. Wherever average precipitation exceeds evaporation and transpiration, calcium tends to leach away. We're especially watchful as we move eastward from about a mid-lowa longitude.
This leaching effect helps explain why historically the Great Plains were an extremely high-quality feed source. The prairie grasses, which supported millions of buffalo, were high in nutrition because of good soil calcium levels.
Dr. Carey Reams, developer of the biological theory of ionization, maintained that calcium is the single most important element in soil chemistry. His explanation of calcium from an energy point of view has been more helpful to me than any other concept in the proper use of calcium in the soil.
Calcium is the primary “anionic” or negatively charged element in the soil. Plants live off the energy that's created as positively charged plant food elements and compounds in soil interact against calcium and other anions.
Soil can't sustain energy release unless available calcium is adequate. It has several effects on soil. For one thing, it mellows the soil. I have operators who've raised the level of calcium to the point that they're now pulling tillage equipment one gear faster with the same tractor. Calcium expands clay particles - literally stacks them in a loose lattice structure. When you add calcium carbonate, the carbonate molecule reacts with water and bacterial action to create gases, which expand the soil, making it more porous - something like yeast expanding a loaf of bread.
I didn't realize until the last several years that calcium feeds soil bacteria. It's one of their absolutely essential nutrients for strong cell walls. You can have all the carbon sources available for energy, but if the calcium isn't there the biological system isn't fed property.
Calcium is a catalyst in critical soil reactions
Calcium also is a catalyst in several soil reactions. Our tab testing this fall has shown that the solubility of calcium rises sharply as the level of biological carbon goes up. Thus calcium is more available in a biologically active soil.
If the soil is biologically dead, the soluble calcium level may be low even though your pH says you don't need to add calcium.
Calcium is also extremely important in the plant's cell strength. It affects the permeability of cell walls. Low permeability means higher osmotic pressure is needed to translocate nutrients and water in the plant. That spells more vulnerability to drought or high salt conditions in soil.
Much of the calcium in the plant is found in leaves and stem. Calcium thickens and strengthens leaves and stems, helping the plant resist disease and weather. Calcium is relatively immobile in the plant, although mobile in soil.
Calcium is also extremely important to a plant's production of proteins. If the calcium is low, the plant sap will be watery because excess nitrogen is pulling in water into the plant without a balance of other nutrients. Because nitrogen has an affinity for water, non-protein nitrogen in the grain will draw water and cause grain to go out of condition even if it's been dried below 15%. We've found that it takes less nitrogen per bushel of crop produced in a soil that has adequate calcium levels and proper calcium- magnesium balance.
It is possible to apply too much calcium. You can overwhelm the nutrients carrying cationic energy, and therefore not have the balance for maximum energy release. This can happen if you apply large amounts of fine lime in the spring. If you're putting on calcium carbonate in the fall, a higher level isn't as touchy.
Our experience has been that excess fine lime applied in spring will cause soil dehydration. It will also tend to dry out the plant, making it more woody.
Calcium is also essential to help the plant build its chlorophyll, the carbohydrate-generation system called chloroplasts. And without that factory working property, the plant can't make adequate plant sugars. If you compare two plants both having a refractometer reading of 8 brix, the plant with adequate calcium will have a sweeter taste.
Liming Materials
We've searched out several good sources of suitable products. It's fairly easy to recommend the right kind of lime; tougher to find an economical source of it close to your farm. Many of the quarries in the upper Midwest are higher in magnesium than we prefer.
Our first choice of a calcium source if it's close enough to you: Calcitic limestone, usually called high-calcium lime. It's calcium carbonate containing less than 5% magnesium; ideally below 2%.
The best grind we've found for lime is 200 mesh. At least 80% of the lime applied should be 200 mesh. The finer the grind, the faster lime will react in the soil.
Apply lime in the fall if possible. Even applying in the winter is better than in spring. If the ground is partially frozen, that’ll help reduce compaction from the application rig. If workload or cash flow prevent fall application, we'd add it to the spring program in reduced amounts, often 25 to 200 pounds.
The recommended amount depends not only on your soil analysis, but the degree of fineness, calcium carbonate equivalent of the lime, and the placement of the lime.
We much prefer to apply several applications of 500 to 1500 pounds per acre over consecutive years, rather than one big dose of two or three tons.
You'll want to leave calcium as near the soil surface as possible instead of plowing it down. It's quite mobile in the soil, and tends to move down with water. We also get better grass weed suppression by keeping calcium on the surface. For example, we'd rather spread lime after fall chiseling or plowing rather than before so there isn't as much dilution. Deep incorporation requires more calcium to get the same benefit.
We normally don't recommend dolomite lime, which we define as a source of lime with 10% or more magnesium. Several reasons:
First, high-magnesium lime becomes available to plants very slowly. Much of the dolomitic lime used today isn't available for at least 18 months, even in a biologically active soil.
Second, the magnesium ties up nitrogen. That increases the amount of nitrogen you'll need per bushel of yield.
Third, magnesium to calcium ratios narrower than 1 to 7 causes a cementing effect in soils as magnesium rises in relation to calcium levels.
The only place where we'd recommend dolomitic limestone would be on soil that's biologically very active, with a very high nitrogen release potential or very high organic matter - but even then in moderation.
Other calcium sources that are very satisfactory: Marl is a mined material containing quite a bit of clay, sometimes peat, and lots of seashells. Normally it will be more effective on a biologically alive soil.
Hydrated lime and quicklime or calcium oxide are good calcium sources. Dr. Reams used to explain how you could use calcium hydroxide to increase soil temperatures. Calcium hydroxide creates lots of electrical resistance in the soil, producing heat as it reacts biologically. We'll never use it in excess of 200 pounds per acre for that purpose, but it can be helpful in limited areas such as high-value crop production. Calcium hydroxide can be very effective applied in irrigation water which contains lots of sulfur to buffer it.
We've learned that adding a carbon source to liquid calcium nitrate and lime in a program will dramatically increase the calcium energy in a soil. Either the calcium used alone or calcium nitrate used alone is not as effective as the two used together. We would normally like to apply the calcium nitrate in the spring at about 1 to 3 gal. per acre, surface applied with nitrogen.
Lime, which has been used in water purification plants, is also a potential source. It's usually inexpensive. But be careful about its heavy metal content. Heavy metals can be damaging in soils and almost impossible to remove because they typically have high atomic weights. Once a heavy metal is in your ground, it takes an element of higher atomic weight or energy value to replace it. Usually that's only possible through long-term bio-degradation.
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