Identifying water needs for yards
Deep and infrequent irrigation key for efficient water use
By Jenna Smith
For more information regarding this subject, contact:
Roger Havlak
(979) 845-4826
rhavlak@tamu.edu
A mature walnut tree sits on a lawn of St. Augustine grass, dotted with crape myrtles, rose bushes, ficus trees and dwarf yaupon hedges. The landscape, along with the sandy loam soil at the Texas A&M Research and Extension Center in Weslaco, makes it the ideal site for studying water requirements of a common residential landscape system, not just of individual plants.
Using sensors placed in 64 different areas and depths, Roger Havlak, extension program specialist for turfgrass and water management with the Texas A&M University Department of Soil & Crop Sciences, measured both potential evapotranspiration from weather stations and actual evapotranspiration. Potential evapotranspiration is the maximum amount of water lost in a cropping system in a given time period from both plants and evaporation. Actual evapotranspiration is the soil moisture loss of a landscaping system consisting of trees, turfgrass and shrubs.
Havlak found that the top eight inches of soil lost the greatest fraction of soil water through plant absorption and evaporation. If the soil moisture content remained high, plants would utilize water in the top eight inches of soil, but, in a water-stressed environment, plants were capable of extracting water from as deep as 24 inches below the topsoil.
"Plants are opportunistic," he said. "They will use as little energy as possible to maintain themselves. If homeowners irrigate lightly and frequently, and do not build water reservoirs deep in the soil, drought conditions that dry the topsoil could possibly injure or even kill the plants. Thus, deep and infrequent irrigation is recommended."
Havlak said system zoning is another useful tool for water conservation. It involves applying water in different zones, separated by water requirements of the plants and application methods. Because water loss rates are normally different among plants in landscapes, he said, this approach is also recommended.
Havlak used the ratio of actual evapotranspiration to potential evapotranspiration to calculate the landscaping coefficient for the Weslaco landscape. Landscaping coefficients remained less than 1 during the study with monthly coefficients ranging from 0.51 to 0.67.
"We are already working with several municipalities to analyze and compare homeowner water consumption rates to weather station potential evapotranspiration rates to determine the number of homeowners possibly overwatering their landscapes as well as the potential savings that may be realized if potential evapotranspiration was used," he said. "This could certainly be a useful tool for municipalities to use in their day-to-day assessments for conserving water."
The potential evapotranspiration value from the weather station was an excellent predictor of water loss rates within the Weslaco landscape system. However, because of the differences among plant varieties and soil types throughout Texas, Havlak and the turfgrass staff at Texas A&M plan to introduce an additional five to ten sites within the next five years.
"We plan on setting up a site at the Texas A&M University Riverside Campus by April 2004 so that we can begin collecting data on that site prior to summer," he said. "We also hope to locate sites in West Texas and New Mexico, both located within the Rio Grande Basin, in the near future."
Havlak has given talks nationwide to water users and to agencies within the turfgrass industry. Local weather stations and county extension offices can also provide homeowners with information on proper irrigation techniques.
