Can you use too much lime?
Perhaps the most frequently asked question by those using our soil fertility program is, “Can I put on a higher rate of lime than you are recommending for this sample?” Generally, this has to do with getting the limestone spread, because the owner of the lime-spreading equipment says he either cannot or will not apply such a small amount.
Many times a farmer has been told, “You can’t use too much lime.” That is not true. From our experience in working with thousands of acres that have previously been over-limed, we know you can easily apply too much lime, not only for crops such as berries and potatoes, but for whatever crop you are intending to grow. And if this happens, it can be far more expensive to correct than the cost of the extra limestone that was not needed, and getting it spread.
Soil Nutrient-Holding Capacity
This capacity is determined by the amount of clay and humus contained in each soil, these being the only portions of any soil that will attract and hold plant nutrients. Once this nutrient-holding capacity is reached, using more of any material containing the element that is already at optimum level will only result in driving off or tying up some other nutrient that should be there and available for use by plants growing in that soil.
The first point to remember when considering this question is that every soil has different characteristics; every soil has a specific capacity to hold each of the elements supplied by any liming material.
Therefore, the capacity of every soil is limited when it comes to attracting and holding calcium and magnesium, the principal elements from limestone. They can help when needed, or hurt when prudent levels are exceeded! Calcium from gypsum can also be very helpful in adequate amounts, but detrimental if the sulfur or the calcium it contains is enough to cause excess thus reducing the availability of other needed nutrients
Misunderstandings concerning whether it is possible to use too much lime continue to exist because of the assumption that if you can apply large amounts of lime on one or more soils somewhere in the world, then all the rest of the soils in the world can stand that much lime too! This is not correct! It can be very costly to the farmer or grower who fails to accurately measure what is there already, whether more is needed, and whether or not any other needed nutrients will be adversely affected if liming is done.
Potential Damage Caught In Time
As an example, a cabbage consultant had us test some soils. He was using high calcium limestone on high pH soils to avoid club root problems. He had extremely heavy clay soils with large nutrient-holding capacities. In the previous 7-10 years, before using our services, he had applied a total of 14 tons per acre of high calcium limestone. His crops had continued to improve.
From our soil analysis we found that all that lime had added just enough calcium to reach the ideal required for his soil. The soils here were so rich that all the other elements were also still there in adequate amounts, so there was no damage due to nutrient tie-up from the large amount of lime applied up to that point.
But now, as the tests showed, his land was to the point that using additional lime, even at one ton per acre, would begin to cause nutrient deficiencies and result in yield reductions. If he just kept on with what he had been doing, even though it had “always” provided better crops, his results would now begin going the other way. Simply assuming that lime should be added for the next crop because it worked on the previous one can be a serious and costly mistake.
So yes, this grower’s soil survived and prospered by receiving 14 tons of lime over a period of less than 10 years, but this is usually not the case; most land would suffer losses long before that.
For example, another client – a neighbor to the client we have just mentioned – needed no high-calcium lime at all on his soils, had never applied any, and had no problem with club root in his cabbage fields, with a pH below 7.0. To do what his neighbor did would have been costly to apply and detrimental to his crops because his soils were entirely different in terms of fertility needs. Adding lime just because it worked for a neighbor, or even for another area on the same farm, can be a serious and costly mistake.
A Result of Excess Lime
Another company hired us to sample and analyze just over 2,000 acres. They had begun having problems with low yields in the past few years. Once the soil test results were examined the problem was obvious. The soils had received so much lime it had severely reduced the capacity to attract and hold enough potassium and caused manganese and zinc deficiencies in the fields that barely had enough even before the lime was applied.
Someone had convinced the owners that you could never apply too much lime. They had applied 6 tons per acre four years before. Yields went up the first year, but then dropped thereafter. Only one field had not received the lime. Fertility there was the best on the farm. All other fields had dropped from 45-50 bushels to 25-30 bushels per acre of soybeans – a crop that tends to benefit greatly from adequate liming. Even with soybeans, too much lime is a detriment.
Too Much Lime May Inhibit Other Nutrients
Normally, applying lime will at least somewhat limit other essential nutrients needed by the plants to be grown there, and the grower should know whether this is the case before using significant amounts of lime. When such is the case, the grower should know this information and also what needs to be done in order to avert the problem. Just knowing the pH will not tell the grower or his consultant this essential information.
To correctly make this type of determination concerning whether liming will help or hurt the soil, a soil test must provide extremely accurate information.
In addition to showing what levels are there, a soil test is most useful when it shows what level should be present and if there will be too much or too little of any other element once the liming is completed. This includes the levels of magnesium, potassium, boron, iron, copper, manganese, and zinc. Failing to measure and determine whether or not any of these are present in borderline amounts and remedying the situation if additional lime is used, can reduce yields even when lime is required and correctly applied, but especially when it is used to excess.
You can absolutely use too much lime on any given soil! Although we have mentioned some successful large applications that are the exception and not the rule, keep in mind that some sandy soils would receive too much lime at a rate of one ton per acre. The key to liming is to measure what the soil requires, supply what is needed as soon as it can be feasibly done, and apply it at the right time to do the job properly.
It takes 3 years to show
What makes identifying the problem somewhat complex is the fact that it may take three full years to see the whole picture of total effects from any lime applied on a field. If too much is used, it is not normally noticeable in the first year. In fact, if some lime was really needed, but substantially less than was spread, improvements will be most evident in the first year. But by the third year, when problems from any excess will then be most evident, many growers have already forgotten the possible long-term effects of the limestone application, and tend to place the blame elsewhere (on weather, fertilizer, seed, and so on).
The adverse effects from over-liming can show up in a number of ways. Principally we must deal with the damage caused from too much calcium and / or magnesium as well as the effects of increasing the soil pH.
Effect on pH
For example, adequate phosphate is a big concern for most farmers in terms of fertilizer. Just by increasing soil pH, phosphate may be released and increased in the soil. But if the pH goes unduly high, phosphates can also be tied up. Using more than enough lime can cause the pH to increase by so much that this happens. In addition, pH can tie up other elements as it increases, such as boron, iron, manganese, copper and zinc.
Effect on Trace Elements
The higher the calcium level climbs from the use of calcium carbonate limestone, or gypsum, or from the calcium make-up of dolomite lime, or any other significant calcium source, the more chance the trace elements, plus potassium and magnesium, have of being tied up in the soil – to the point that the crops can no longer take them up. Then plants suffer in terms of quality and yield. This is also a critical point to understand, if the levels of any of these elements, which can be tied up by too much calcium or too high a pH, are already borderline in the soil (in terms of availability for plant use), deficiencies can occur unless they are able to be determined beforehand by testing, and treated accordingly.
Effect on water use
Use of calcium also increases the pore space in the soil. This is a desirable result until pore space reaches 50% of the total soil volume. But when too much calcium is applied by over-liming, so much pore space can result that the soil dries out much easier than before. So you can lose efficiency of water use, whether it’s from rainfall or irrigation, if you over-lime your soils.
Consider all sources
Some growers might think that just as long as there is not too much limestone applied, there is no problem. High calcium limestone (calcium carbonate) and gypsum ( calcium sulfate) are generally considered the most common sources of calcium. But the problem can be caused by other materials too. The list includes oyster shell, rock phosphate, kiln dust, marl rock (ground sea shells), sugar beet processing lime, and stack dust from the scrubbers of utilities or industrial facilities burning high sulfur coal. All of these, as well as poultry manure, especially from laying hen operations (where calcium is supplemented to strengthen the egg shells) can be a significant source of additional calcium. Compost should also be suspect until the actual calcium content is accurately determined. Also certain types of wood ashes that are applied at high tonnage rates, and some sources of irrigation water, can contribute substantially to the levels of calcium in the soil.
Don’t be fooled, too much calcium can cost you money in terms of lower crop yields. On the other hand, even in crops such as berry or potato, so called “low pH crops”, too little calcium, or too low of a pH, can cost you just as much or more, if not corrected.
Use a soil test.
The best way to determine what is actually needed or not needed in terms of liming is to use a detailed soil analysis. The soil analysis should include measurement of calcium and magnesium and the percentage saturation of each in the soil. (As we explain in Hands On Agromony, growers cannot determine whether lime is required simply by measuring the pH of the soil.) The soil testing methods used by Kinsey Agricultural Services always include checking for both calcium and magnesium levels to determine if there is too little, too much or if the proper amount is already there. Chapters 2 through 4 of Hands On Agronomy help explain this in greater detail. An overall picture of what over-liming actually does to a soil can be seen by taking a soil sample prior to the use of the lime and following up each year for the next three years.
So when someone asks, “Why can’t we just go ahead and apply 2000 lbs anywhere that you call for less than that?” the answer is: if you can never apply too much limestone, that would be fine. But too much limestone can be a potential problem for the soil and for the crops to be grown there, because it can tie up other nutrients also needed for the growing crop. So it is far better not to use too much lime.
Yet when needed, applying the correct amount of lime makes a real difference to how your crops are going to respond, whatever crop you may choose to grow there.
– Neal Kinsey
