Chapter 19

Management of Vineyard Soils

Acidic Vineyard Soils

Acidity is due to hydrogen (H+) ion concentrations in the soil, therefore, the higher the hydrogen concentration, the lower the pH in the soil. Excessive soil acidity can reduce growth and yield of grapevines, and potentially cause fruit quality problems. American grape varieties can tolerate pH values as low as 5.5 while Vitis vinifera varieties are more susceptible to acidic soil conditions.

Main Causes of Soil Acidification

Soil acidification occurs naturally in high rainfall areas such as the eastern U.S. and some mountainous and coastal regions of the western U.S. Water from rainfall slowly dissolve minerals containing exchangeable bases and leach them from the soil. Basic cations (sodium, Na+; calcium, Ca2+; magnesium, Mg2?; potassium, K?) are replaced with hydrogen from rainwater, making the soil acidic.

Managing Acidic Soils

Soil acidity can only be corrected by neutralizing the acid present, which is done by adding agricultural limestone. When added to the soil, even though liming materials are not the same, they all follow the same process to neutralize soil acidity.

Liming Materials

A number of materials are available for liming acid soils. The selection of a liming material should be based on its ability to neutralize soil acidity, chemical composition, fineness of grind, ease of handling, and cost.

Calcium Carbonate Equivalent

As with most sedimentary materials, limestone varies in purity and chemical composition. In order to compare the acid neutralizing value of various liming materials, the Calcium Carbonate Equivalent (CCE) test uses pure calcium carbonate (CaCO3) as the standard assigning an arbitrary index of 100 percent to define its neutralizing value.

Particle Size of Liming Materials

The effectiveness of a liming material in correcting soil acidity depends not only on purity, but also on fineness of the material. Fineness of grind is important for calcium and/or magnesium carbonate materials because carbonate materials have a very low solubility in water. As fineness increases, the rate of reaction increases.

Lime Requirements and Application Rates

The application rate of liming material is calculated based on the pH requirements of the grape rootstock and scion, the buffer pH, soil texture, the depth of soil to be neutralized, and the effective calcium carbonate equivalent of the liming material.

Reaction Rate of Limestone

Not only does the reaction rate of limestone depend of the particle size of the limestone it also depends on the soil pH and the degree of mixing of lime with the soil.

Application Methods

Incorporation can be done by either applying the lime to the soil surface and cultivating and/or during deep ripping and subsequent cultivation. It may be more efficient to feed lime down a tube behind the ripper when ripping the soil rather than applying it directly on the surface. In established vineyards, lime applications are most effective when they are spread uniformly and thoroughly mixed with the soil by plowing and disking, close to the vine root zone.

Time of Liming Applications

The best time to apply lime is prior to vineyard establishment when it can be mixed into the soil by cultivation before vineyard establishment. In established vineyards lime can be applied at any time of the year if weather and soil conditions permit but generally it is applied in the fall.

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