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Handbook of Soils for Landscape Architects$
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Robert F. Keefer

Print publication date: 1999

Print ISBN-13: 9780195121025

Published to Oxford Scholarship Online: November 2020

DOI: 10.1093/oso/9780195121025.001.0001

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Effective Water Use—Irrigation

Effective Water Use—Irrigation

(p.83) 8 Effective Water Use—Irrigation
Handbook of Soils for Landscape Architects

Robert F. Keefer

Oxford University Press

Soils that are suitable for irrigation are deep soils that are permeable and have a high available water-holding capacity (usually containing much organic matter). Limitations for irrigation include presence of restrictive layers (pans), erodible soils, sloping land, susceptibility to stream overflow, salinity or alkalinity, stoniness, and hazard of soil blowing. The amount of plant-available water in a soil depends on rooting depth and soil texture. Coarse textured sands hold much less available water than finer textured clayey soils. Available water increases as the texture becomes finer up to a silt loam. Any soil texture finer than that results in no additional increase in available water. In shallow soils, the rooting depth is limited by the soil depth. In deep soils, root depth is determined by the kind of plants present: . . . Trees and large shrubs 48 inches depth Medium shrubs and vines 40 inches depth Small shrubs and ground cover 24 inches depth . . . A number of techniques can be used to determine when water should be applied to soil in which plants are growing. These techniques include observing the plants, especially for wilting; feeling the soil; using tensiometers or electrical resistance meters installed in the soil; and measuring temperatures of plant leaves. Wilting—When plants begin to lose water they droop and wilting results. If plants remain in this condition very long, they soon die. It is better to water plants before they become wilted. Any plant that is wilted will require some time to reestablish its water equilibrium, thereby slowing the growth of that plant. The amount of moisture in a soil can be roughly estimated by the “feel method”. The degree of moisture can be determined by rolling or squeezing the soil into a ball. The soil moisture condition can be divided into six categories from dry to very wet: . . . a. If a ball will not form → soil is too dry for plants. b. If the ball formed will not crumble when rubbed → soil is too wet for plants. . . .

Keywords:   field capacity, foliar temperature, water holding capacity

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