This Fact Sheet helps turf managers assess their irrigation water by using four key water properties that are listed on water reports and four key soil properties listed on soil salinity and texture reports. The second half of this Fact Sheet provides six illustrative case-studies for bermudagrass lawns to model site-specific irrigation strategies.
Four Key Irrigation Water Properties
Total salts is typically reported in units of milligrams per liter (mg/L) as TDS (total dissolved solids) or TSS (total soluble salts); for all practical purposes, TDS and TSS are interchangeable terms. However, TDS and TSS are often indirectly measured as EC (electrical conductivity) multiplied by 0.64. While EC is the historical method of classifying irrigation water, total salts makes more intuitive sense; either can be used (Table 1).
Table 1. Classification of irrigation water based on total salts (mg/L or ppm) and EC (µS/cm or µmhos).
|320-960||500-1500||Good||Little concern, especially with periodic rainfall|
|960-1920||1500-3000||Fair||Leach salts from soil as needed|
|1920-3200||3000-5000||Poor||Routinely leach; monitor soils|
|3200-3840||5000-6000||Very Poor||Requires special attention; consult water specialist|
|>3840||>6000||Unacceptable||Do not use|
The SAR (sodium adsorption ratio) is used for determining the ratio of sodium to calcium and magnesium in soils. This relationship is important because sodium strips calcium from soil particles and prevents soil aggregates from forming and creating flow paths in the soil. Although SAR is typically a soil parameter, it can also be used to classify irrigation water (Table 2) because that water will eventually determine the salt chemistry of the soil. The SAR is unitless because it is a ratio.
Table 2. Classification of irrigation water based on SAR.
|1-2||Good||Little concern, add pelletized gypsum periodically|
|2-4||Fair||Aerify soil, sand topdress, apply pelletized gypsum, monitor soils|
|4-8||Poor||Aerify soil, sand topdress, apply pelletized gypsum, monitor soils closely, leach regularly|
|8-15||Very Poor||Requires special attention; consult water specialist|
|>15||Unacceptable||Do not use|
The Adj SAR (adjusted sodium adsorption ratio) is another parameter typically used for soils. It adjusts for lost calcium in the form of calcium carbonate deposits. This calcium loss essentially increases the SAR of irrigation water and decreases the soil’s ability to form soil aggregates. Use Adj SAR when it exceeds the unadjusted ratio. The regular classification system for SAR (Table 2) is still used after the adjustment.
The SAR and total salts together help predict water infiltration rates. Infiltration rates are improved by high total salts, but high salts may damage turfgrass. Therefore, water with high salts can be helpful (Figure 1, page 2) and harmful (Table 1) simultaneously.
Boron is a nutrient, but in high concentrations is toxic to plants. In addition, boron is difficult to leach from the soil. It requires about three times the water to leach boron from the soil as it does salts. Water containing less than 1.0 mg/L boron should be of no concern for most plant materials, while water with more than 2.0 mg/L boron is unsuitable for irrigation use.
Four Key Soil Properties
The TSS (total soluble salts) in soil is similar to that in water; the difference is that the classification limits are higher (Table 3).
Table 3. Classification of soil extracts based on TSS (mg/L or ppm) and EC (µS/cm or µmhos).
|2560-5120||4000-8000||Above Normal||Little concern, especially with periodic leaching|
|>5120||>8000||Saline||Leach regularly with best available water|
ESP (exchangeable sodium percent) is the percent of soil exchange sites occupied by sodium. Few laboratories actually measure this relationship; instead, they calculate ESP from SAR. Since the relationship between calculated ESP and SAR are proportional, either parameter can be used to classify sodium in soil (Table 4).
Table 4. Classification of irrigation water based on ESP and SAR.
|≥12||≥15||Sodic||Aerify soil, sand top dress, apply pelletized gypsum, leach regularly with best available water
Boron in soil can be toxic to plants, depending on boron concentrations and plant sensitivity. Ornamental trees and shrubs are sensitive at levels above 0.5 mg/L boron. At boron levels above 2.0 mg/L, Kentucky bluegrass is sensitive. Most other turfgrass are not sensitive until the levels are above 6.0 mg/L.
Soil texture is the percent sand, silt, and clay in the soil. Soils with high clay content have very low permeability rates. The permeability rates for sandy soils are very high. Texture analysis can be performed by turf professionals using texture-by-feel or by soil laboratories.
Cisar, J., Kopec, D., Park, D., & Soldat, D. (Eds.). (2012). Aquatrols guide to assessing and managing turf salinity issues in irrigation water and soils. Retrieved from http://s3.amazonaws.com/aquatrols/20121022113516.pdf
Duncan, R. R., Carrow, R. N., & Huck, M. T. (2009). Turfgrass and landscape irrigation water quality. Boca Raton, FL: CRC Press.
Harivandi, M. A. (1999). Interpreting turfgrass irrigation water test results (Publication #8395). Retrieved from the University of California Division of Agriculture and Natural Resources website http://anrcatalog.ucanr.edu/pdf/8009.pdf
Landschoot, P. (2016). Irrigation water quality guidelines for turf sites. Retrieved from the PennState Center for Turfgrass Science website http://plantscience.psu.edu/research/centers/turf/extension/factsheets/water-quality
Landschoot, P. (2013). Irrigation water quality guidelines for sports turf. SportsTurf, 29(10), p. 18-20.
PACE Turf (2010, Apr.). Water quality guidelines. Retrieved from https://www.paceturf.org/PTRI/Documents/water/0502water.pdf
Park, D. M., McCarty, L. B., & White, S. A. (n.d.). Interpreting irrigation water quality reports. Retrieved from the Clemson University website https://www.clemson.edu/public/regulatory/ag_svc_lab/irrigation_water/water_interpretation.pdf
Peacock, C. H., Miller, G. L., & Matthew, C. M. (n.d.). Irrigation water quality problems (Publication AG-759-W). Retrieved from the North Carolina Cooperative Extension Service website http://www.turffiles.ncsu.edu/Files/Turfgrass/Articles/Peacock_C/2012/AG-759_Irrigation_Water_Quality_ProblemsDealing_with_a_Management_Challenge.pdf
Turfgrass Water and Environment
Research and Extension Specialist
Turfgrass Water Quality Laboratory Manager