Grapevine Water Management
Soil and Water Relationships
Irrigation water management requires an understanding of the water-holding capacity of a soil, particularly in the root zone of the grapevines; with the water-intake rate of the soil; with the root system of the vines to be grown; and with the amount of water that the vines requires. There are four important levels of soil moisture content (See Figure 11.2) that reflect the availability of water in the soil. They are commonly referred to as: 1) saturation, 2) field capacity, 3) permanent wilting point, and 4) plant available water.
Saturation
Saturation is the point the soil pores are filled with water. Saturation usually occurs for short periods of time, either during heavy rainfall events or when soil is being irrigated.
Filed Capacity
Field capacity defines the amount of water remaining in a soil after downward gravitational drainage has stopped. This value represents the maximum amount of water that a soil can hold against gravity following saturation by rain or irrigation.
Permanent Wilting Point
The amount of water a soil contains after vines are wilted beyond recovery is called the permanent wilting point.
Plant Available Water
The amount of water held by the soil between field capacity and the permanent wilting point is referred to as plant available water. Plant available water is typically expressed in terms of inches of water per inch of soil depth.
Management Allowable Depletion (MAD)
Only a portion of the water content can be potentially removed from a volume of soil by the vines and, this quantity is called management allowable depletion (MAD).
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Soil Type
Sandy soils have many large pores and very little clay resulting in little available water. Water applied by drip irrigation tends to move vertically rather than horizontally in these soil types due to gravity pulling the water through the large pores.
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