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- 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.
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