In Search of Wine Quality: Soil and Water---Part 2

Part 2. Water Holding Capacity
In my last blog, In Search of Wine Quality: Soil and Water, the topic was about "Soil Type and Texture". Knowing the type of soil texture is important because that determines the water holding capacity of the soil. The water holding capacity of the soil is the product of:¹

Some definitions:

• Hygroscopic water is moisture that is held too tightly in the soil to be used by plants
• Capillary water is moisture that is held in the pore spaces of the soil and can be used by plants
• Gravitational water drains rapidly from the soil and is not readily available to be used by plants.
• Field capacity is the maximum amount of water that the soil can hold against gravity; the boundary between gravitational water and capillary water; it is the upper limit for soil moisture that is usable by plants
• Permanent wilting point would be a point where there's no water left for the plant; represents the boundary between capillary water and hygroscopic water

Here is how the definitions apply to a soil cross section:²

Looking from left to right on the above diagram shows how water interacts with the various soil textures. Knowing the water holding capacity of the soil is important because the optimum crop growth and health occurs when the soil moisture content is held between 50 – 80% of the “plant available water”. Especially for grape vines, the soil should not be too wet nor should it be too dry, it should be just right.
For more information on watering holding capacity, please check out this blogpost: Soil Texture and Water Holding Capacity.
Next installment of "In Search of Wine Quality" will be about soil drainage. Who knew that there was so much dirt on soils. (I know, cheap shot.)
References:
1. Alan N. Lakso and Tim E. Martinson, The Basics of Vineyard Site Evaluation and Selection, Department of Horticulture, Cornell-Geneva.
2. Steve A. Miller, Powerpoint presentation on Irrigation Scheduling and
 Soil Moisture Monitoring, Biosystems and Agricultural Engineering, Michigan State University. (The link provided will download the presentation.)