Rick Galceran
El Paso Water Utilities
El Paso, Texas
Narrative Summary:
Managers and superintendents of golf courses, parks, and school grounds and other large landscape installations are faced with increasing public or budgetary demands to use non-potable water, including reclaimed sewage water or salty water, for irrigation. Salt problems are among the constraints that ground maintenance professionals are aware of, yet are difficult to assess with certainty. This study was conducted to help improve guidelines for appraising potential salt hazards through the exploratory survey of large landscaping areas where salty water has been used for irrigation.
The reconnaissance survey of 14 golf courses in the Southwest and Southern California has shown that salt problems begin to appear when salinity of irrigation water exceeds about 500 ppm. When it exceeds 1000 ppm, salt problems are common, and include both foliar and root-induced salt damages. Foliar-induced salt damage caused by direct sprinkling on tree forages was found to be quite extensive, affecting many tree species. However, this problem is relatively easy to control through modification of irrigation schedules and/or systems.
Root-induced salt damage occurs when salts accumulate in the soil in excess of the levels that a given plant species can tolerate. For many of the species currently used in the Southwest, soil salinity should be kept below 3 dS m ' for sensitive species and 6 dS m ' for moderately tolerant species. To maintain soil salinity below the target levels, the soil must be permeable and drainable. Our soil salinity survey performed for the El Paso City Park systems irrigated with water of 600 to 800 ppm with an average sodicity of 5. 8 in SAR indicates that the necessary salt leaching may not be attained in soil having texture than loam, such as clay loam or clay, or those having subsoils indurated with caliche, even when salinity of irrigation water is well below 1000 ppm. Soil salinity of silty clay loam or silty day has reached in the excessive range of 16 to 34 dS m ' in a matter of 20 years (Table 1). When salinity of irrigation water exceeds about 1000 ppm, its use may have to be restricted to highly permeable and drainable sandy soils, unless funds are available for extensive soil modification. Likewise, soil sodicity of silty clay loam reached nearly 30 in SAR (Table 1). The level of salt ac lation in soils was correlated to the saturation water content, a measure of soil texture (Fig. 1), and soil sodicity to salt accumulation (Fig. 2). These data indicate that soil sodicity, besides soil salinity can increase to a level of inducing sodium hazards in soils having poor permeability or high water tables, even when irrigated with water having a SAR as low as 5.0.
Topography plays an important, but usually secondary role in affecting salt accumulation in soils. Our soil salinity survey conducted at two golf courses in El Paso indicates that land slopes and formations have had relatively small effects on the mean soil salinity. However, the extent of variability was significantly increased under complex topography (Table 2). This means that the chances of developing localized salt spots will increase substantially under the complex land forms.
The above case studies indicate that appraisal of potential salt problems based solely on water quality analysis is too simplistic. Soil testing and profile examination for salt leaching must be made to avoid costly errors. Soil samples should be collected using a soil map and/or topographical features as a work for sampling. For a statistically meaningful assessment of soil salinity, three to ten samples may be needed in an area consisting of the same soil type and topography. If the decision to use salty water for irrigation is made, soil salinity should be monitored, and appropriate adjustments in management should be followed. (Additional information on this subject may be obtained from the Texas A&M University, Agricultural Research Center via Fax (915) 859-1078 or E-Mail address, s-miyamoto@tamu.edu).
This project is supported by a cooperative project agreement between El Paso Water Utilities, US Bureau of Reclamation, and the Texas A&M University Agricultural Research Center at El Paso.
