Chapter 19

Management of Vineyard Soils

Physical Soil Properties

A soil’s physical properties have a lot to do with its ability to produce crops. The plant support, root penetration, drainage, aeration, retention of moisture, and plant nutrients are linked with the physical condition of the soil. Physical properties also influence the chemical and biological behavior of soil. The physical properties of a soil depend on the amount, size, shape, arrangement and mineral composition of its particles. These properties also depend on organic matter content and pore spaces. Some of the more important physical properties of a soil include soil horizons, texture, structure, porosity, permeability, and color.

Parent Material

The soil profile is comprised of two or more soil layers called horizons, one below the other, each parallel to the surface of the land. Important characteristics of the various horizons are:

Rock Types

Soil minerals form the basis of soil. They are produced from rocks (parent material) through the processes of weathering and natural erosion. Water, wind, temperature change, gravity, chemical interaction, living organisms and pressure differences all help break down parent material.

Soil Horizons

The soil profile is comprised of two or more soil layers called horizons, one below the other, each parallel to the surface of the land. Each horizon of soil may be different from the other horizons in physical or chemical ways— color, texture, structure, consistence, porosity, and soil reaction. The differences are developed from the interaction of such soil-forming factors as parent material, slope, native vegetation, weathering, and climate.

Soil Depth

The depth of the soil, the distance from the surface to an impervious layer or an area of poor drainage, is one of the most important factors for determining the success of a vineyard. A soil with a depth greater than 3 feet (0.9 m) offers a greater volume of potential soil moisture than does a shallow soil. However, it doesn’t imply that grapevines can’t be grown on shallow soils, but these vines will be the first to suffer drought stress if supplemental water is not available by irrigation. Not to mention vines with shallower root systems are more affected by annual variations in rainfall having a greater effect on the vintage.

Soil Structure

Soil structure refers to the arrangement of soil particles (sand, silt, and clay) into stable units called aggregates (known to soil scientists as peds). Aggregation is important for increasing stability against erosion, for maintaining porosity and soil water movement, and for improving fertility and carbon sequestration in the soil. Welldeveloped structure allows favorable movement of air and water, while poor structure retards movement of air and water making it difficult for grapevines to grow.

Soil Porosity

Soil porosity, or pore space, is the volume percentage of the total soil that is not occupied by solid particles. Soil texture and structure influence porosity by determining the size, number and interconnection of pores. Coarse-textured soils have many large (macro) pores because of the loose arrangement of larger particles with one another. Finetextured soils are more tightly arranged and have more small (micro) pores.

Effects of Porosity on Infiltration Rates

Clay soils have numerous micropores and hold large quantities of water, but since they have few macropores they produce very slow infiltration rates. The pores in the clays may be so small and hold water so tenaciously that the water is not available to the vines.

Soil Texture

Soil texture refers to the composition of the soil in terms of the proportion of small, medium, and large particles (clay, silt, and sand, respectively). For example, a coarse soil is a sandy soil or loamy sand, a medium soil is a loam, silt loam, or silt, and a fine soil is a sandy clay, silty clay, or clay.

Effects of Texture on Water and Nutrient Availability

Texture is an important soil characteristic because it will, in part, determine water intake rates (infiltration); water movement through soil (hydraulic conductivity); soil water holding capacity; the ease of tilling the soil; and the amount of aeration (which is vital to root growth). Water infiltrates more quickly and moves more freely in coarsetextured or sandy soils, which increases the potential for leaching of mobile nutrients (e.g., nitrate-NO3?). Sandy soils also hold less total water and fewer nutrients for grapevines than fine-textured soils.

Soil Permeability

Soil permeability is a measure of the ease with which air and water move through the soil. A consistent and moderate supply of water, along with deep and spreading root growth are some of the benefits of good drainage or permeability.

Soil Color

Color of soil is an important feature in recognizing different soil types, but color is also an indicator of certain physical (i.e., internal drainage) and chemical characteristics.

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