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Water, Leaves, and Soil

As temperatures start getting higher, water evaporation increases, creating water deficiencies in the soil independent of the amount of rain we receive in a given time. This is the reason why irrigation is necessary during the summer months (water evaporates faster as days and hights get hotter).When water is applied to the soil it seeps down through the root zone very gradually.

Each layer of soil must be filled to “field capacity” before water descends to the next layer. This water movement is referred to as the wetting front. Water moves downward through a sandy coarse soil much faster than through a fine-textured soil such as clay or silt. If only one-half the amount of water required for healthy growth of your garden or landscape is applied at a given time, it only penetrates the top half of the root zone; the area below the point where the wetting front stops remains dry as if no irrigation has been applied at all.

Once enough water is applied to move the wetting front into the root zone, moisture is absorbed by plant roots and moves up through the stem to the leaves and fruits. Leaves have thousands of microscopic openings, called stomates, through which water vapor is lost from the plant. This continual loss of water called transpiration, causes the plant to wilt unless a constant supply of soil water is provided by absorption through the roots. The total water requirement is the amount of water lost from the plant plus the amount evaporated from the soil.

These two processes are called evapotranspiration. Evapotranspiration rates vary and are influenced by day length, temperature, cloud cover, wind, relative humidity, mulching, and the type, size and number of plants growing in a given area. Water is required for the normal physiological processes of all plants. It is the primary medium for chemical reactions and movement of substances through the various plant parts. Water is an essential component in photosynthesis and plant metabolism, including cell division and enlargement. It is important also in cooling the surfaces of land plants by transpiration. Water is a primary yield-determining factor in crop production. Plants with insufficient water respond by closing the stomata, leaf rolling, changing leaf orientation and reducing leaf and stem growth and fruit yield. Not all water is suitable for use as an irrigation source. Prior to implementing an irrigation system, the water source should be tested for water quality. The instructions for testing and the testing results may be obtained from the Texas AgriLife Extension Service or an independent water lab.

The results of the test will determine if the water is suitable for irrigation or reveal if any special tactics will be required to overcome quality deficiencies. Major factors in determining water quality are its salinity and sodium contents. Salinity levels are expressed as categories based on conductivity. Sodium is a major component of the salts in most saline water but its impact can be detrimental to soil structure and plant growth beyond its status as a component of salinity. The level of sodium (Na) in irrigation water is another important factor of quality. There are critical growth periods when water stress is most detrimental. It is imperative that a good moisture supply be maintained during seed germination and seedling emergence from the soil. Water transplants immediately. Many shallow-rooted plants and newly planted trees and shrubs suffer water stress. Wilting followed by browning leaf tips and edges are signs of water stress. To determine if irrigation is needed, feel the soil in the soil zone where most roots are located. As you gain experience feeling the soil and observing plant symptoms, it will help you time irrigations.

For more information on this on other agricultural topic please contact the Hopkins County Extension Office at 903-885-3443 or email me at [email protected].

Mario Villarino DVM, Ph.D. Hopkins County Extension Agent for Ag and NR 1200B Houston Street Sulphur Springs, Texas 75482 903-885-3443
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