Natural Notes: Water Management
This post consists of my notes from a lecture on water management for urban trees as part of a training to become a certified arborist by the International Society of Arborculture. The speaker was Brenda Ochhiuzzo, a natural resources specialist with the Forest Preserves of Cook County and her lecture took place on January 23, 2015 at the Salt Creek Resource Management facility in Willow Springs, Illinois.
Introduction
Water is vital to all plants. Plants absorb water which allows them to take in dissolved minerals from the soil via their roots. Up to 95% of that water is transpired into the air. See figure 1. Too much water can cause damage. Trees in urban areas need proper irrigation and drainage.
Trees and Water
The amount of water used by a tree varies on the species. Some are adapted to withstand dry periods by transpiring less. Transpiration is controlled by the stomatal openings.
Infiltration is water absorption into the soil whereas percolation is water movement in the soil. Infiltration varies by soil texture. Water can move up, down, and laterally. Water moves down when there is infiltration and laterally when their is percolation in the soil.
Available water is held within the micropores of soil.
Soil and Water requirements
Wilting is where transpiration exceeds water absorption. If the tree's cells do not become turgid by morning, the tree may become seriously stressed and could lead to further wilting, leaf loss, and an increased amount of absorbing roots (figure 2). In a severe drought, a permanent wilting point means death.
Irrigation
Frequent shallow watering encourages surface rooting. More water less frequently is better because it encourages deeper roots and as such the tree will be more drought tolerant.
Drip irrigation is another option and it slowly drips out water which in turn reduces runoff, erosion, and water loss.
Water Conservation
Freshwater is a limited resource in urban environments. Minimum irrigation should be practiced to ensure plant health. It involves an understanding water budgets as it relates to plant and soil water loss.
Xeriscaping can be done in drought prone areas using drought tolerant species. Hydrozones are plantings that require a similar watering schedule. A tensiometer is a soil probe used to monitor moisture. The use of recycled water, or gray water, should be used with caution as it can be high in salts, chemicals, phosphorous (sometimes), nitrogen, and sulfur. Sandy soils are preferred for good drainage and salt tolerant plants should be used. Less frequent, longer irrigation should be performed to reduce salt buildup.
Other practices that can be used to increase soil moisture includes mulching. Mulch may improve soil structure and infiltration. It can reduce soil moisture evaporation, moderate soil temperature, reduce weed competition, reduce erosion, and can add organic matter to the soil as it breaks down.
Other Water Conservation Practices
Do not fertilize during dry periods, as it may cause fertilizer burn.
Antitranspirants can be sprayed onto leaves to reduce water loss. It creates an impermeable coating that closes stomata. Antitranspirants can be phototoxic and may increase stress on a plant's health.
Flooding
Flooding occurs when soil moisture is above field capacity. Flooding damage to trees includes a lack of oxygen, suffocation of roots, alteration of the chemical composition of elements, mineral toxicities, and fermentation. Longer flooding leads to more problems.
Drainage
Avoid creation of low spots. Install drain tiles, add soil amendments that add macrospore space (re-aerating), or install rain gardens.
Introduction
Water is vital to all plants. Plants absorb water which allows them to take in dissolved minerals from the soil via their roots. Up to 95% of that water is transpired into the air. See figure 1. Too much water can cause damage. Trees in urban areas need proper irrigation and drainage.
Trees and Water
The amount of water used by a tree varies on the species. Some are adapted to withstand dry periods by transpiring less. Transpiration is controlled by the stomatal openings.
 |
| Figure 1: Water is absorbed by a tree's roots and then is transpired. |
Available water is held within the micropores of soil.
Soil and Water requirements
Wilting is where transpiration exceeds water absorption. If the tree's cells do not become turgid by morning, the tree may become seriously stressed and could lead to further wilting, leaf loss, and an increased amount of absorbing roots (figure 2). In a severe drought, a permanent wilting point means death.
 |
| Figure 2: Turgid versus flaccid plant cells. |
Frequent shallow watering encourages surface rooting. More water less frequently is better because it encourages deeper roots and as such the tree will be more drought tolerant.
Drip irrigation is another option and it slowly drips out water which in turn reduces runoff, erosion, and water loss.
Water Conservation
Freshwater is a limited resource in urban environments. Minimum irrigation should be practiced to ensure plant health. It involves an understanding water budgets as it relates to plant and soil water loss.
Xeriscaping can be done in drought prone areas using drought tolerant species. Hydrozones are plantings that require a similar watering schedule. A tensiometer is a soil probe used to monitor moisture. The use of recycled water, or gray water, should be used with caution as it can be high in salts, chemicals, phosphorous (sometimes), nitrogen, and sulfur. Sandy soils are preferred for good drainage and salt tolerant plants should be used. Less frequent, longer irrigation should be performed to reduce salt buildup.
Other practices that can be used to increase soil moisture includes mulching. Mulch may improve soil structure and infiltration. It can reduce soil moisture evaporation, moderate soil temperature, reduce weed competition, reduce erosion, and can add organic matter to the soil as it breaks down.
Other Water Conservation Practices
Do not fertilize during dry periods, as it may cause fertilizer burn.
Antitranspirants can be sprayed onto leaves to reduce water loss. It creates an impermeable coating that closes stomata. Antitranspirants can be phototoxic and may increase stress on a plant's health.
Flooding
Flooding occurs when soil moisture is above field capacity. Flooding damage to trees includes a lack of oxygen, suffocation of roots, alteration of the chemical composition of elements, mineral toxicities, and fermentation. Longer flooding leads to more problems.
Drainage
Avoid creation of low spots. Install drain tiles, add soil amendments that add macrospore space (re-aerating), or install rain gardens.
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