Management of Vineyard Soils
The physical properties of a soil are those characteristics of a soil such as soil horizons, texture, structure, porosity, permeability, and color. In turn, these properties affect air and water movement in the soil, and thus the soil’s ability to function.
Soil Development 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. Important characteristics of the various horizons are:
Parent material refers to material from which the soil has been derived and, in most cases, is of geological origin. The nature of the parent material can have a profound influence on the characteristics of the soil. The mineralogy of the parent material is mirrored in the soil and can determine the weathering process and control the natural vegetation composition.
The bedrock geology includes many lithologies, often classified into three types based on origin: igneous, metamorphic, and sedimentary
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 doesnít imply that grapevines canít be grown on shallow soils, but these vines will be the first to suffer drought stress if supplemental water is not available by irrigation.
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).
Soil structure refers to the arrangement of soil particles (sand, silt, and clay) into stable units called aggregates (known to soil scientists as peds), which give soil its structure. 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.
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.
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 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. Grapes need good internal soil drainage to grow. Wet soils restrict root growth and respiration, resulting in weak growth, reduced yields and small vine size.
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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