Magazine: (Part.1) Managing Turfgrass Using Poor Quality Water

By Jerry Spencer in Consultancy on 6th Dec 2007 20:20

PART 1

Increasingly a large number of golf courses and other amenity turf areas are using effluent water for irrigation. The result of utilizing this water source is that the effects of excess soluble salts can become apparent on turfgrass areas. As a direct result of this water analysis and periodic monitoring have thus become key components of sound irrigation management.

Water analysis by a commercial laboratory provides data on many parameters, some of which are of little significance for turfgrass

Sewage effluent water before and after AFM filtration

irrigation. The most important parameters for turfgrass management are total concentration of soluble salts (salinity); sodium (Na) content; relative proportion of sodium to calcium (Ca) and magnesium(Mg) (Sodium Adsorption Ratio or SAR); chloride (Cl), boron (B), bicarbonate(HCO3), and carbonate (CO3) content; and pH.

Other parameters that you are likely to find on a water test report and that you should review are nutrient content (nitrogen, phosphorus, and potassium), chlorine content, suspended solids, and turbidity, though none of these by itself plays a major role in determining the suitability of water for irrigation.

IMPORTANT TEST PARAMETERS
Salinity. All irrigation waters contain some dissolved mineral salts and chemicals. Some soluble salts are identified as nutrients and are beneficial to turfgrass growth (such as N, P, K etc; others may be phytotoxic or may become so when present in high concentrations. The rate at which salts accumulate to undesirable levels in a soil depends on their concentration in the irrigation water, the amount of water applied annually, annual precipitation (rain plus snow), and the soil’s physical and chemical characteristics.

Different laboratories report water salinity in different ways: as Total Dissolved Solids (TDS) measured in parts per million (ppm) or milligrams per liter (mg/L), or as electrical conductivity (ECw) measured in millimhos per centimetre (mmhos/cm), micromhos per centimetre (µmhos/cm), decisiemens per metre (dS/m), or siemens per metre

Some labs may also report the individual components of salinity (e.g., sodium) in milliequivalents per litre (meq/L). You can use the following equations to convert results from one set of units to another, and so compare data from differently formatted reports:
(1) 1 ppm = 1 mg/L
(2) 1 mg/L = meq/L x Equivalent Weight (see Table 1)

Table 1. Conversion factors for mg/L and meq/L
	To convert	To convert
	mg/L to meq/L	meq/L to mg/L
Constituent	multiply by	multiply by

Sodium (Na)	0.043	23
Calcium (Ca)	0.050	20
Magnesium (Mg)	0.083	12
Bicarbonate	0.016	61
Carbonate	0.033	30
Chloride (Cl)	0.029	35

(3) 1 mmho/cm = 1 dS/m = 1,000 µmhos/cm = 0.1 S/m
(4) ECw (mmhos/cmor dS/m) x 640 = TDS (ppm or mg/L)

Note that the 640 value is a general average factor and may require adjustment in special circumstances. For example, waters containing substantial amounts of sulphate require a higher conversion factor.

Most water that is acceptable for turfgrass irrigation contains from 200 to 800 ppm soluble salts. Soluble salt levels greater than 2,000 ppm may injure turfgrass; salt levels up to 2,000 ppm may be tolerated by some turfgrass species (Table 2), but only on soils with exceptional permeability and subsoil drainage. Good permeability and drainage allow a turfgrass manager to leach excessive salts from the root zone by periodically applying heavy irrigations of more desirable water such as that from a town water supply. Sand-based sport fields and golf greens have the proper soil structure for this form of salinity management. (It should be noted that irrigation water with a very low salt content [i.e., below 0.2 dS/m] can actually reduce the permeability of a soil. Such water can disperse clay particles, which then clog large soil pores that are important for good permeability.)

Table 2. Relative tolerances of Australian turfgrass species to soil salinity (ECe)

Sensitive (<3 dS/m)	Moderately sensitive (3 to 6 dS/m)	Moderately tolerant (6 to 10 dS/m)	Tolerant (>10 dS/m)
Poa annua	Annual ryegrass	Perennial ryegrass	Bermudagrasses
Colonial bentgrass	Creeping bentgrass	Tall fescue
Kentucky bluegrass	Fine-leaf fescues
	Buffalograss

From:M.A.Harivandi,J.D.Butler,and L.Wu.1992.Salinity and turfgrass culture. In D.V.Waddington,R.N.Carrow,and
R.C.Shearman (eds.) Turfgrass,pp.207–229.Series No.32.Madison:American Society of Agronomy.

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