Re-examination of water quality criteria for assessing wastewater suitability for irrigation

Re-examination of water quality criteria for assessing wastewater suitability for irrigation Steve Grattan, Ph.D Department of Land, Air and Water Resources University of California, Davis

Multiple types of waste waters Food processing waste water Reclaimed municipal waste water Dairy waste waters Agricultural drainage water

Renewal of the NPDES (National Pollutant Discharge Elimination System) permit EPA State Water Resources Control Board University of California, Davis Wastewater Treatment Story ECw < 0.7 ds/m

GUIDELINES FOR INTERPRETATIONS OF WATER QUALITY FOR IRRIGATION (Ayers & Westcot) Potential Irrigation Problem Units None Degree of Restriction on Use Slight to Moderate Salinity(affects crop water availability) 2 Severe EC w µhmos/cm < 700 700 3,000 > 3,000 (or) TDS mg/l < 450 450 2000 > 2000 Infiltration(affects infiltration rate of water into the soil. Evaluate using EC w and SAR together) 3 SAR = 0 3 and EC w = > 0.7 0.7 0.2 < 0.2 = 3 6 = > 1.2 1.2 0.3 < 0.3 = 6 12 = > 1.9 1.9 0.5 < 0.5 = 12 20 = > 2.9 2.9 1.3 < 1.3 = 20 40 = > 5.0 5.0 2.9 < 2.9 Specific Ion Toxicity (affects sensitive crops) Sodium (Na) 4 surface irrigation SAR < 3 3 9 > 9 sprinkler irrigation me/l < 3 > 3 Chloride (Cl) 4 surface irrigation me/l < 4 4 10 > 10 sprinkler irrigation me/l < 3 > 3 Boron (B) 5 mg/l < 0.7 0.7 3.0 > 3.0 Trace Elements (see Table 21) Miscellaneous Effects (affects susceptible crops) Nitrogen (NO 3 - N) 6 mg/l < 5 5 30 > 30 Bicarbonate (HCO 3 ) (overhead sprinkling only) me/l < 1.5 1.5 8.5 > 8.5 ph Normal Range 6.5 8.4

FAO 29 (Ayers and Westcot, 1985) Valuable reference for irrigation managers and consultants internationally Guidelines in Table 1 (p. 8) developed as management tool and provide a conservative approximation of water quality standards that protects all crops in all Mediterranean and arid climates, in a wide range of soil types over the long-term. Ayers and Westcot, 1985

FAO 29 (Ayers and Westcot, 1985) Inorganic water quality criteria for assessing water suitability 1. Salinity hazard (ECw) 2. Hazard posed by specific-ion toxicity (Cl, B, Na) 3. Water infiltration hazard (EC and SAR)

Relative Yield % Characterizing Salinity-Yield Relations Maas and Hoffman, 1977 100 % Yield = 100 b(ece a) a Steppuhn et al., 2004 50 b a Average Rootzone Salinity (ECe) Grieve et al., 2012

Crop salt tolerance % Yield = 100 b(ece a) 100 50 Maas and Grattan, 1999 1 2 3 4 5 6 7 8 9 10 Average Rootzone Salinity (ECe)

How does one relate soil salinity thresholds (ECe) to irrigation water criteria (ECw)? EC w = electrical conductivity of the irrigation water EC e = electrical conductivity of the saturated soil paste Irrigation Management!

Leaching Fraction (%) LF = volume of water that drains below the rootzone / volume of water that infiltrates the ground Amount of water applied Amount of water drained LF = Volume Drainage water / Volume of infiltrated water

Salinity distribution in relation to various leaching fractions ET Same irrigation water ECw Soil Depth Low LF 40% 30% 20% High LF 10% Steady-state conditions ECe

Average Root Zone ECe (ds/m) 10 9 Conventional Irrigation Leaching Fraction = 5% 10% 8 20% 7 6 5 4 3 30% 40% 50% 2 1 0 1 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 EC of Irrigation Water (ds/m)

What EC w limit is most appropriate? Depends on the assumed leaching fraction Depends on what crops are being considered Depends upon soil type Depends on climate and whether rainfall is considered Depends on irrigation management and method of irrigation

Other questions related to developing site-specific water quality limits Protect the most sensitive of the dominant crops (those representing 95% cropped area)? What level of protection (100, 95, 90% yield potential)? Protect for all years or 90% of the years?

The model The model determines the average rootzone salinity (ECe) over the season taking into account the salinity of the irrigation water and a number of sitespecific factors including crop type, soil type, climate (daily rainfall, temperature), irrigation practices (method, LF, interval), soil water movement, root water extraction, ET and leaching. Isidoro and Grattan, 2010

EC e changes over the year ECw = 0.7 ds/m Transient model; Isidoro and Grattan, 2010

1951 1954 1957 1960 1963 1966 1969 1972 1975 1978 1981 1984 1987 1990 1993 1996 1999 2002 ECe (ds/m) Seasonal average rootzone salinity over the 53 year period In Corn Capay soil, ECw = 1.4 ds/m 2,4 2,2 2 1,8 1,6 1,4 1,2 Yield = 95% Yield = 100% 1 0,8 0,6 0,4 0,2 0 Soil Cc, corn ECw = 1.4 ds/m Goal is to develop probability distribution Year Ayers and Westcot (1985) for corn ECw = 1.1 ds/m

Probability of average rootzone ECe exceeding the threshold Simulation of all 53 years Corn Capay soil

Winter concentrated rainfall reduces seasonal ECe more than rainfall distributed evenly across the year

Other transient-state LF models ENVIRO-GRO HYDRUS-2D SALTMED TETrans UNSATCHEM Adds a time element to leaching. Models include various degrees of complexity with multiple components; bypass flow, chemical speciation in the soil water, soil hydraulic properties, ET, irrigation frequency, crop salt tolerance, combined salinity-matric stress, etc.

Are steady-state models overly conservative and/or obsolete? Steady-state models overestimate the LR and exaggerate the negative effects of irrigating with saline water. But, steady-state models are not obsolete because they can be used as first approximation for water suitability. Before transient models can be adopted, they need to be user friendly with adequate sophistication to accurately predict soil water dynamics and predict how plants respond to heterogeneous conditions where soil salinity varies over space and time. No models exist that meet these criteria. Corwin and Grattan, 2018

FAO 29 (Ayers and Westcot, Inorganic water quality criteria for assessing water suitability 1. Salinity hazard (ECw) 2. Hazard posed by specific-ion toxicity (Cl, B, Na) 3. Water infiltration hazard (EC and SAR)

Ion toxicity Boron (B), Chloride (Cl) and sodium (Na)

Toxic Ion Accumulation Transpiration Scion Rootstock Soil water

Rootstock Controls Cl toxicity Almond UC Davis Kutman et al., 2015

Chloride Toxicity in Almond Carmel/ Hansen Nonpareil/ Nemaguard

Chloride (Cl) tolerance criteria in Ayers and Westcot (1985) are based on Cl concentration in soil water. Similar Cl w criteria can be developed as they were for EC w New information on rootstock tolerances to Cl are continuously introduced in the literature

Cl more toxic than Na in Almond Kutman et al 2015

FAO 29 (Ayers and Westcot, Inorganic water quality criteria for assessing water suitability 1. Salinity hazard (ECw) 2. Hazard posed by specific-ion toxicity (Cl, B, Na) 3. Water infiltration hazard (EC and SAR)

Sodic water effects soil physical conditions Adverse effects on soil physical properties increasing soil crusts and reduces infiltration Reduced Oxygen Diffusion to roots Nutritional disorders Increased susceptibility to disease Soft water makes hard soils and hard water makes soft soils

The traditional criteria for assessing sodicity Sodium Adsorption Ratio (SAR) Units are mmol c /L

Sodicity Sodium Adsorption Ratio 35 30 EC, SAR and Infiltration Hazard Severe Reduction in Infiltration Slight to Moderate Reduction in Infiltration 25 20 15 10 No Reduction in Infiltration 5 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 EC of Irrigation Water (ds/m) Salinity

SAR 50 40 30 Unstable Unstable Quirk and Schofield, 1955 20 10 Rhoades, 1982 0 Adapted from Suarez, 2012 10 20 30 40 50 Concentration (mmolc/l)

Flocculating power of cations normalized to Na K = 1.8 Mg = 27 Ca = 45 Rengasamy and Summer, 1998

Cation Ratio of Soil-structural Stability (CROSS) CROSS = (Na + 0.56K) / [(Ca + 0.60 Mg) / 2] 1/2 Rengasamy and Marchuk, 2011

Cation Ratio of Soil-structural Stability (CROSS) Note: CROSS > SAR Sposito et al., 2016

Key points The ECw limits varies as it is related to water management, LF, crop type, level of protection, soil type rainfall. The ECw criteria based on steady-state conditions is overly conservative and can be adjusted upward accounting for transient conditions and rainfall. Tree and vine crops are particular sensitive to ion toxicity (Cl and Na) which is controlled by rootstock. New information continues to be developed. Sodicity indirectly impacts crops by destruction of soil structure (infiltration, aeration, mechanical strength) which can be corrected by increasing free Ca 2+ in soil solution. The traditional SAR criteria should be replaced by CROSS which more accurately accounts for the dispersive contributions of K and reduced flocculating power of Mg and is more appropriate for waste waters of variable compositions.

Thank you

Salinity-induced calcium deficiency Grieve et al, 1998