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Magazine: (Part.2) Managing Turfgrass Using Poor Quality Water

By Jerry Spencer in Consultancy on 6th Dec 2007 20:50

Part 2

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The parameters a turfgrass manager should consider in evaluating irrigation water quality. As indicated, waters with ECw values greater than 0.7 dS/m (450 mg/L) present increased salinity problems. Only careful management will prevent the accumulation of deleterious amounts of salts in the soil if water with a high ECw is used for irrigation. Avoid using any water with an ECw above 3 dS/m.

The salt tolerance of turfgrass and other plants is expressed in terms of the salt content of the soil root zone. For example, as indicated in Table 2 Kentucky bluegrass will tolerate a soil salinity (ECe, the electrical conductivity of the soil water extract) of up to 3 dS/m. You must therefore consider soil physical characteristics and drainage, both of them important factors in determining root zone salinity, when you decide about the suitability of a given irrigation water. Water with an Ecw of 1.5 dS/m may be suitable for grass grown on sandy soil with good
drainage (and thus high natural leaching), but the same water may prove injurious within a very short period if used to irrigate the same grass grown on a clay soil or a soil with limited drainage resulting from salt buildup in the root zone.

Table 3. Guidelines for the interpretation of water quality for irrigation
		Degree of restriction on use
Potential	Unit		Slight to
irrigation problem		None	moderate	Severe

Salinity
ECw	dS/m	<0.7	0.7 to 3.0	>3.0
TDS	mg/L	<450	450 to 2,000	>2,000
Soil water infiltration
(evaluate using ECw [dS/m] and SAR together)
if SAR = 0 to 3 & ECw =		>0.7	0.7 to 0.2	<0.2
if SAR = 3 to 6 & ECw =		>1.2	1.2 to 0.3	<0.3
if SAR = 6 to 12 & ECw =		>1.9	1.9 to 0.5	<0.5
if SAR = 12 to 20 & ECw =		>2.9	2.9 to 1.3	<1.3
if SAR = 20 to 40 & ECw =		>5.0	5.0 to 2.9	<2.9
Specific ion toxicity
Sodium (Na)
root absorption	SAR	<3	3 to 9	>9
foliar absorption	meq/L	<3	>3	—
	mg/L	<70	>70	—
Chloride (Cl)
root absorption	meq/L	<2	2 to 10	>10
	mg/L	<70	70 to 355	>355
foliar absorption	meq/L	<3	>3	—
	mg/L	<100	>100	—
Boron (B)	mg/L	<1.0	1.0 to 2.0	>2.0
Miscellaneous effects
	meq/L	<1.5	1.5 to 8.5	>8.5
^{Bicarbonate (HCO}3⁾
(unsightly foliar deposits)	mg/L	<90	90 to 500	>500
pH		normal range	6.5 to 8.4
Residual chlorine (Cl2)	mg/L	<1.0	1 to 5	>5
Adapted from D. W. Westcot and R. S. Ayers. 1984. Irrigation water quality criteria. In G. S. Pettygrove and T. Asano (eds.)
Irrigation with Reclaimed Municipal Wastewater – A guidance manual. Report No. 841-1wr. California State Water Resources Control Board, Sacramento, CA; and from D. S. Farnham et al. 1985. Water Quality: Its Effects on Ornamental Plants. University of California Division of Agriculture and Natural Resources Publication 2995.

The figures in Table 2 give a general guide to the salt tolerance of individual turfgrasses. As indicated, soils with ECe values below 3 dS/m are considered satisfactory for most turfgrasses. ECe values between 3 and 10 dS/m indicate soils in which only a few salt-tolerant turfgrass species can survive.

Sodium. Sodium content is another important factor in irrigation water quality evaluation. Plant roots absorb sodium and transport it to leaves where it can accumulate and cause injury. The leaf symptoms of sodium toxicity resemble those of salt burn. Because salts can be absorbed directly by leaves, irrigation water with a high evel of sodium salts can be particularly toxic if applied to plant leaves via overhead irrigation. Among grasses grown on golf courses, Poa annua and bentgrass are the most susceptible to sodium phytotoxicity.

SAR (Sodium Adsorption Ratio). Although sodium in the irrigation water can be toxic to plants, a more common deleterious effect of sodium results from its effect on soil structure. This effect generally is a major concern for golf course superintendents and other turf managers. When irrigation is applied to the soil, the best indicator of sodium effect is a water’s Sodium Adsorption Ratio (SAR), a value which should be provided in all laboratory water analyses. As a general rule, water with an SAR value below 3 is considered safe for turf and other ornamental plants (Table 3).

SAR is such an important factor in water evaluation, that it merits a thorough understanding. The high sodium content common to recycled water can cause deflocculation (breakdown) of soil clay particles, severely reducing soil aeration and water infiltration and percolation. In other words, a soil’s permeability is reduced by irrigation with water high in sodium. The best measure of a water’s likely effect on soil permeability is the water’s SAR considered together with its ECw. SAR is the ratio of the concentration of sodium ions to the concentration of calcium plus magnesium. You can use the formula below to calculate SAR if a laboratory report does not provide it but does provide values for sodium, calcium, and magnesium in meq/L. I

f values are provided as mg/L or ppm, convert them to meq/L using the conversion factors in Table 1 before you use the formula.

Generally, water with an SAR greater than 9 can cause severe permeability problems when applied to fine-textured (clay) soils over a period of time. Coarse-textured (sandy) soils have fewer permeability problems and can tolerate an SAR of this magnitude. For example, you can successfully irrigate golf greens and sports fields constructed with high-sand-content root zone mixes using high-SAR water because of their good drainage.

For waters high in bicarbonate, some laboratories adjust the calculation of SAR (yielding an “adjusted SAR” or “Adj. SAR”) because soil calcium and magnesium concentrations are affected by the water’s bicarbonate. In simplest terms, Adj. SAR reflects the water’s calcium, magnesium, sodium, and bicarbonate content as well as its total salinity. Other labs use a newer method to adjust the SAR value and report the adjusted value as Adj. Rna.

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Magazine: (Part.2) Managing Turfgrass Using Poor Quality Water

Table 3. Guidelines for the interpretation of water quality for irrigation

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