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Winegrowing -

July / August 1999 

Liming of Vineyard Soils

By Thomas J. Rice, PhD
Soil Science Department, California Polytechnic State University, San Luis Obispo, CA

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

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.

Table II - Amounts of lime required

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.

References

1. California Fertilizer Association. 1995. Western Fertilizer Handbook. 8th edition. Interstate Publishers, Inc., Danville, IL.
2. B.D. Doss, W.T. Dumas, and Z.F. Lund. 1979. "Depth of lime incorporation for correction of subsoil acidity." Agron. J. 71(4): 541-544.
3. Himelrick, D.G. 1991. "Growth and nutritional responses of nine grape cultivars to low soil pH." Hort. Science 26: 269-271.
4. Miller, R.W., and D.T. Gardiner. 1998. Soils in our environment. 8th edition. Prentice Hall Publ., Englewood Cliffs, NJ.
5. Robinson, J. (editor). 1997. The Oxford companion to wine. Oxford Univ. Press, New York, NY.
6. Tisdale, S.L., W.L. Nelson, J.D. Beaton, and J.L. Havlin. 1993. Soil fertility and fertilizers. 5th edition. Macmillan Publ. Co., New York, NY.
7. Wright, R.J., V.C. Baligar, and R.P. Murrmann (ed.). 1991. "Plant-soil interactions at low pH. Developments in plant and soil sciences." Kluwer Acad. Publ., Netherlands.

You can contact Dr. Thomas Rice, in California by fax at 805/756-5412, or by e-mail: trice@calpoly.edu. You can also phone him in San Luis Obispo, CA, at 805/756-2420.

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