Liming vineyard soils to increase soil pH and raise calcium levels has
been practiced for centuries in the humid areas of the world where soils tend
to be more acid. Today, liming is increasingly practiced in the semiarid
central coast regions of California, where liming of vineyards was unheard of
even a decade ago.
Past agricultural practices, such as the addition of sulfur, acid-forming
nitrogen fertilizers, and organic soil amendments, have caused soil
acidification. Previously, most of these lands were either open space, range
lands, or planted to grain crops.
To avoid unnecessary expense and protect the soil from environmental
degradation when lime is used as a soil amendment, growers must assess their
vineyards carefully to determine the proper types and amounts of liming
materials to add.
What is lime?
Generally the term "lime," or "agricultural lime,"
refers to all limestone-derived materials used to neutralize acid soils,
including ground limestone (calcium carbonate; CaCO3), hydrated lime (calcium hydroxide;
Ca(OH)2), or burned lime (calcium oxide; CaO), with or without
additions of magnesium carbonate, magnesium hydroxide, or magnesium oxide. In
strict chemical terminology, lime refers to calcium oxide (CaO).
Quick field test for lime
To test for the presence of lime in your vineyard, take a spoonful of soil
and drop a few drops of muriatic acid or 10% hydrochloric acid on it. If
bubbling or fizzing occurs (due to carbon dioxide gas, CO2), this indicates the presence of carbonates or
bicarbonates (lime). A quantitative determination of soil lime content requires
laboratory analysis.
Lime and soil considerations
Adding lime increases soil pH, improves microbial activities, and increases
the availability of nitrogen (N) and phosphorus (P). Adding excessive lime is
expensive and undesirable for many reasons. Although the cost of lime,
resultant yield increases, and increased grape quality determine the net
benefit derived, lime is usually a profitable soil additive on strongly acidic
(pH below 5.0) soils.
The following three facts about liming soil are particularly important:
- Lime additions generally improve soil structure, especially in clay soils,
and in combination with phosphorus, may give larger increases in yields than
lime alone.
- Toxic levels of soluble and exchangeable aluminum (Al) can be almost
eliminated by raising the pH to between 5.2 and 5.5 with lime; further liming
to a pH between 6.0 and 6.5 usually increases yields. The beneficial effects of
raising the pH from 5.3 to 6.5 is likely due to an increase in biological
activity, which increases the available nitrogen (N), molybdenum (Mo), and
calcium (Ca).
- Adding high amounts of lime (raising pH higher than 6.5) may require
addition of plant nutrients, such as iron (Fe), zinc (Zn), manganese (Mn), and
phosphorus (P), which become less available to plants at a pH greater than 7.5.
How much lime to apply
To arrive at a satisfactory solution to the problem of how much lime to
apply, the pH requirements of the grape rootstock and scion, the pH and buffer
capacity, and cation exchange capacity (CEC) of untreated soil should be
considered. The most satisfactory means of determining liming needs is by soil
tests. Soil samples should be taken at least every three years.
The lime needs within a vineyard can be interpreted most accurately when a
detailed soil survey report and map are produced and the various soil series in
the vineyard are identified. The soil series descriptions will characterize
soil texture, structure, mineralogy, and other root-zone characteristics, such
as humus content and permeability, which will affect the lime response.
There is a relationship between texture, CEC, and buffering capacity —
resistance to a change in ion concentration. The more clay and organic matter
there are in a soil, the more lime is needed to change the pH, because the soil
colloids may contain large quantities of exchangeable Al and H ions due to
their high CECs.
The amount of pH change desired and the type of clay mineral present also
affect the amount of lime needed to change the pH. The relative amount of lime
needed in soil of the same initial pH with the following principal clay
minerals decreases as we move through the list of vermiculite, montmorillonite,
illite, kaolinite, and sesquioxides (metal oxides).
Methods of applying lime
If needed, lime can be applied to advantage at any stage in the
establishment of a vineyard. It is usually recommended to add lime several
months ahead of rootstock planting to allow time for resultant pH changes.
Lime is usually applied by spreading it on the soil surface. Newly spread
lime should be well mixed at least one foot deep, prior to planting of grape
vines. On strongly acidic soils, where more than three tons per acre (TPA) of
lime are required, half the amount may be applied before soil ripping and the
other half applied and disked in after ripping and prior to rootstock planting.
When less than two TPA of lime are needed, the entire amount may be applied
and disked in before planting. When both surface soils and subsoils are
strongly acidic (pH below 4.5), it sometimes pays to incorporate lime to a
depth of at least 12 inches.3 Lime will not react
well in the soil unless it is incorporated into the soil. Therefore, it will
not work well in no-till vineyards, but can work well in high rainfall areas
with lots of earthworms.
Application depth of liming materials
Surface applications of lime without some degree of mixing in the soil are
not immediately effective in correcting subsoil acidity. In several studies it
was observed that 10 to 14 years were required for unincorporated,
surface-applied lime to increase the soil pH at a depth of six inches. For
fairly high rates, broadcasting half of the lime at the soil surface and
disking the other half is a satisfactory method of mixing lime in the upper
foot of soil.
Neutralization of subsoil acidity through deep incorporation of
surface-applied lime is possible with the tillage equipment now available. With
no-till vineyard systems, where the vineyard cover crop is mowed and not
cultivated, the surface soil pH can decrease substantially in a few years
because of the acidity produced by the decomposition of plant residues.
Fortunately, the increased acidity is usually concentrated in the topsoil,
where it often can be readily corrected by surface liming.
Time and frequency of liming
applications
In vineyards with cover crops that include legumes, lime should be applied
three to six months before the time of seeding; especially on very acid (pH
below 4.5) soils. Lime may not have adequate time to react with the soil if
applied just before the cover crop seeding.
Frequency of application generally depends on the soil texture, N source and
rate, crop removal, precipitation patterns, and lime content. On sandy soils,
frequent light applications in the winter are preferable, whereas on
fine-textured soils, larger amounts may be applied less often during the rainy
season. Finely divided lime reacts more quickly, but its effect is maintained
over a shorter period than that of coarse materials.
Lime balance sheet
When a soil has had its acidity reduced (pH increased) by lime, how often
must lime be added and how much is needed to keep the soil pH suitable?
The answers depend upon the rate of lime loss. Lime is neutralized or lost
from the soil by such activities as:
- Neutralization by acid-forming fertilizers (ammonium-nitrogen;
NH4-N), which produces a rapid change.
- Neutralization by the acid formed by carbon dioxide dissolved in water
(from air, biological respiration, and organic matter decomposition), which is
a slow continual process.
- Leaching of alkaline soil materials below the root zone, such as calcium
carbonate, which produces a slow change.
- Removal in harvested or grazed crops, which produces a slow loss.
- Erosion. As topsoil is eroded, more acidic subsoil may be exposed.
Liming materials
The anion accompanying any cation (usually Ca2+) must lower
H+ activity in the soil solution. Gypsum (CaSO4 .
2H2O) and other neutral (pH near 7.0) salts cannot neutralize H+, as
illustrated in the following reaction:
Gypsum (CaSO4 . 2H2O) + 2H+ <—->
Ca2+ + 2H+ + SO42- +
2H2O
As seen above, the H+ levels are the same on each side of the
equation; therefore, no pH change has occurred.
Liming reactions begin with the neutralization of H+ in the soil
solution by either OH- or HCO3- originating
from the liming material. For example, CaCO3 behaves as follows:
CaCO3 + H2O —-> Ca2+ +
HCO3- + OH-
The rate of the reaction is directly related to the rate at which the
OH- ions are removed from solution. As long as sufficient
H+ ions are in the soil solution, Ca2+ and
HCO3- will continue to go into solution. When the
H+ ion concentration is lowered, formation of the Ca2+
and HCO3- ions is reduced.
Neutralizing value of liming materials
The materials commonly used for liming soils are Ca and/or Mg oxides,
hydroxides, carbonates, and silicates (Table I). The
value of a liming material depends on the quantity of acid that a unit weight
of it will neutralize, which in turn, is related to the molecular composition
and purity.
Table1
Neutralizing value (CCE) of pure
forms of some liming materietals |
| Liming Material |
Neutralizing value % |
| Ca0 |
179 |
| Ca(OH)2 |
136 |
| CaMg(CO3)2 |
119 |
| CaCO3 |
100 |
| CaSiO3 |
86 |
| Source: Western Fertilization
Handbook |
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Pure CaCO3 is the standard against which other liming materials are
measured, and its neutralizing value is considered to be 100%. The
calcium-carbonate equivalent (CCE) is defined as the acid-neutralizing capacity
of a liming material expressed as a weight percentage of CaCO3.
Magnesium carbonate (MgCO3) will neutralize 1.19 times as much
acid as the same weight of CaCO3; hence its CCE is 119%. The same
procedure is used to calculate the neutralizing value of other liming
materials.
Quality and fineness of limestone
Agricultural limestone’s effectiveness depends on the degree of
fineness, because the reaction rate depends on the surface area in contact with
the soil. CaO and Ca(OH)2 are powders, but most limestones must be
crushed to reduce the particle size and increase the surface area.
Because the cost of limestone also increases with fineness, materials that
require minimal grinding, yet contain enough fine material to change pH
rapidly, are preferred. Agricultural limestones contain both coarse and fine
materials. Many states in the U.S. have laws that require that 75% to 100% of
the limestone pass an 8- to 10-mesh screen and that 25% pass a 60-mesh screen.
This way, there is fairly good distribution of both the coarse and fine
particles.
Fineness is quantified by measuring the distribution of particle sizes in a
given limestone sample. The effective calcium carbonate (ECC) rating of a
limestone is the product of its CCE (purity) and the fineness factor.
Lime requirement: Different methods have been developed to determine
the amount of lime needed to bring the pH of an acid soil to a desirable range.
All of those analytical methods presently used take into consideration the
buffering capacity of the soil.
A major problem of managing acid soils is to estimate the quantity of lime
required to raise the soil pH to a certain level (see Table II). Non-legumes, such as grapes, can derive
nitrogen from nitrogen fixed in legume cover crops. Much of the vine response
to liming may actually be the pH responding to nitrogen fixation by the
legume-Rhizobium relationship in a cover crop containing legumes.
 Although many people still regard the primary effect of lime to
be the provision of adequate soil calcium, its main value is really the
addition of hydroxyl (OH- ) ions to the soil solution:
CaCO3 + H2O====> Ca2+ +
HCO3- + OH-
The hydroxyl ions produced from the lime neutralize soil acidity, raise soil
pH, and thus provide the most important effects of the liming process.
Increased quantities of soluble and exchangeable calcium and magnesium are
merely by-products of liming, although their greater amounts in limed soils may
be beneficial to plants having high calcium requirements, such as legumes, and
the increased calcium will help improve soil structure.
Conclusion
The decision to add lime to increase soil pH should depend on the goals of
the vineyard manager relative to rootstock and scion selection. If lime is to
be added, it is best to incorporate it at least one foot deep prior to planting
of rootstock.
In established vineyards, there is no economical and effective method to
significantly raise the subsoil pH by liming. The best one can hope for is to
raise the pH of the upper six inches of soil and to increase the decomposition
rate of any cover crop residue. Therefore, it is best to obtain a detailed soil
map and soil test information prior to vineyard establishment to make a wise
decision regarding soil liming.
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