25 Sep Top 10 Liming Questions
Published by the Samuel Roberts Noble Foundation, Inc., February 2002
by Jeff Ball
- How long does it take for lime to work?
Since water is required for lime to react with the soil, effects of a lime application will be slower in a dry soil. It often takes a year or more before a response can be measured even under perfect conditions. However, a response may be observed within weeks of the application when soil pH is extremely low. It is important to apply lime immediately after the growing season or crop removal to allow lime to react, correcting soil pH before the next growing season.The reactivity time also depends on the type of lime used. Liming materials differ widely in their neutralizing powers due to variations in the percentage of calcium and/or magnesium. Usually, liming materials with a high calcium carbonate equivalent (CCE) tend to neutralize soil acidity faster than those with a low CCE. The coarseness of the liming material will also influence how fast the lime will react. In other words, the finer the liming material, the greater the surface area, resulting in faster reactivity.
- How little or how much lime can be applied at one time?
The amount of lime needed depends on the type of crop being grown. If growing continuous wheat or bermudagrass, it is only necessary to raise the soil pH above 5.5. Therefore, one-half ton or 25 percent of the soil test deficiency amount required to raise the soil pH to 6.8 is recommended. If growing legumes, the soil pH needs to be raised to 6.8. If surface applying lime, apply no more than two and one-half tons per acre per year. Up to four tons per acre may be applied if the lime is worked into the soil. In situations where soil pH is extremely low and a large amount of lime is recommended, it may be a good idea to spread the cost over two to three years by annually applying one-third or half of the lime needed.
- Should lime be worked into the soil or placed on the surface?
Whenever possible, tillage should be used as a tool to incorporate lime into the soil. When lime is worked into the soil, a larger portion of its surface area is exposed to the soil allowing for faster reactivity.Lime applied on the soil surface does not react as fast as lime incorporated by tillage, but what other option is there in perennial pasture systems? Surface-applied lime moves into the soil at a slow rate. It is similar to non-mobile nutrients in its movement in the soil. However, there are a few crops that have roots that feed close to the soil surface, such as bermudagrass and alfalfa. It has been documented that correcting pH in the top two to three inches of the soil has a positive effect on forage production. Even though it is best to incorporate lime whenever possible, it is still important to surface-apply lime to correct the soil acidity problem in established pastureland and no-till cropping systems.
- Does liming have an effect on herbicide activity?
There are several herbicide families that are soil pH dependent. For example, low soil pH levels may reduce the activity or residual time of triazine (atrazine, Sencor) and sulfonylurea (Peak) herbicides. High soil pH levels (>6.8) tend to increase herbicide activity that increases the risk of crop injury and/or carryover potential.
- What effect do different tillage systems have on soil pH?
All lime calculations are based on neutralizing the acidity in the top six inches of soil. As a result, different tillage systems affect soil acidity. A conventional tillage system involves several tillage passes over the field prior to planting. If the subsoil is calcareous, deep tillage may mix enough subsoil into the top six inches to maintain soil pH at the surface. Conventional tillage systems allow the opportunity to thoroughly mix applied lime prior to the next growing season. A conservation tillage system is not as aggressive as conventional. Fewer tillage passes may be implemented prior to planting, leaving greater than 30 percent crop residue on the soil surface. As a result, there is a limited amount of soil mixing. It is critical to closely monitor soil pH in no-till systems since most lime and dry fertilizer is surface-applied. Over time, the top inch of soil may become extremely acidic due to the surface application of fertilizer. However, soil surface pH can also become too high if a large amount of lime is applied at one time and left on the soil surface. It is best to apply small amounts of lime more frequently to maintain soil pH in a no-till system.
- Are dolomitic sources of lime better than calcitic?
In general, soils in Oklahoma and north Texas are not deficient in magnesium. Therefore, the use of dolomitic lime to increase soil magnesium levels is not important. Dolomitic lime may be recommended in pastures that have a history of grass tetany to raise forage magnesium levels. Both calcitic and dolomitic lime sources work well in raising soil pH. In our region, it is more important to look at the cost effectiveness rather than the source.
- What are the advantages and disadvantages of liquid lime verses dry lime?
Liquid lime is a formulation of approximately 50 percent high quality dry Ag lime (usually greater than 90 percent) and 50 percent H2O. It has the advantage of providing better uniformity of spread over the field in comparison to dry lime. There are three main disadvantages of liquid lime. First, there are normally higher operational costs since you must haul both water and lime across the field. Secondly, under-liming is more likely to occur with liquid lime due to spread rate. Finally, more frequent lime applications are often needed since liquid lime reacts quicker than a dry lime source, but the rate may not be high enough to correct all the reserve acidity. One must be very careful of the rate at which liquid lime is applied. It is appealing to the producer because of its fast reaction time and uniformity advantages. It is important to know how much active ingredient or neutralizing power that you are paying for.
- What is the cost effectiveness of liquid lime products versus agricultural lime?
To make a decision about the cost effectiveness of these two products, one must compare both the total neutralizing power/unit weight of each and the cost/unit weight of each. This area can quickly become rather complicated. If you have any questions in comparing the cost of liquid and dry lime, we would be more than glad to provide assistance.
- Why is the difference in soil pH and buffer pH on the soil test report?
pH is an unbuffered measure of the hydrogen ion concentration in the soil (active acidity) whereas buffer pH is a measurement of total soil acidity (active + reserve acidity). Soils with low buffering capacities (low cation exchange capacity or CEC) usually have less total acidity than soils with a high CEC if the pH is the same. Therefore, it takes less lime to correct the total acidity in a soil with a low CEC. The buffer pH on the soil test report is used to calculate how much lime is needed to correct both the active and reserve acidity. When soil pH is 6.5 or greater, the buffer index will not be reported on the soil test report due to its irrelevance.
- How often should I apply lime?
The answer to this question depends on a variety of considerations. A soil with a low CEC does not require a lot of lime to correct soil pH, but may need to be limed frequently. A soil with a high CEC requires a large amount of lime to initially correct pH, but it may be several years before another lime application is needed due to its high buffering capacity. The level of production also dictates how often lime will be needed. As fertilizer is applied to enhance forage or crop production, the removal of essential plant nutrients from the soil also increases. As a result, lime may be needed more frequently to replenish removed nutrients. For example, the rate of nutrient removal from a pasture being hayed is much greater than a pasture being grazed. Therefore, the hay field may need to be limed more often.
© 1997-2011 by The Samuel Roberts Noble Foundation, Inc.
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