Turf Irrigation Water Quality: A Concise Guide

Published May. 2017|Id: HLA-6612

By Justin Quetone Moss, Michael Kress

Jump To:

Four Key Irrigation Water Properties
Four Key Soil Properties
Further Reading

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).

Total Salts	EC	Classification	Management
<320	<500	Excellent	None
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.

SAR	Classification	Management
<1	Excellent	None
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
5-15	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.

Total salts and SAR are used together to predict the effect of irrigation water on infiltration hazard.

Figure 1. Total salts and SAR are used together to predict the effect of irrigation water on infiltration hazard. (Adapted from Harivandi, 1999).

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).

TSS	EC	Classification	Management
<2560	<4000	Normal	None
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.

SAR	ESP	Classification	Management
<12	<15	Normal	None
≥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.

Six Illustrative Case Studies for Bermudagrass Lawns

Six Illustrative Case Studies for Bermudagrass Lawns cont’d

Extension

Turf Irrigation Water Quality: A Concise Guide

Four Key Irrigation Water Properties

Four Key Soil Properties

Further Reading

Was this information helpful?