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War. Sci. Tech. Vol. 40. No.2, pp. 97-103.1999C ImlAWQ

Publishedby ElsevierScienceLtdPrinted in GrealBritain. All rights reserved

0273-1223199520.00 + 0.00

IRRIGATION WATER QUALITY ANDFARM MANAGEMENT DECISIONS

O. D. Kuchanwar, C. K. Kale, V. P. Deshpande andD. M. Dharmadhikari

National Environmental Engineering Research Inst itute, Nehru Marg.Nagpur 440 020, India

ABSTRACT

The quantity and quality of water available for irrigation is variable from place to place in India. There areregions where the farmers have no access to any surface water body. nor do they have any ground watersource yielding water of acceptable quality for irrigation. In some of the coastal areas, neither surface waternor ground water of acceptable quality may be available. In such areas, setting up an indusU)' andtransporting good quality surface water from long distances 10 the site may be useful for fanners in theadjacent areas; the treated wastewater from the industry may constitute a dependable source for irrigation.This paper gives a brief account of some of these peculiar situations.

Whatever the situation, it is necessary that the water used for irrigation is of an acceptable quality for thecrop concerned. growing on the soil of the site. For a given crop. during its growth cycle, it is essential thatthe concentration of the soil solution around the root zone with regard to dissolved solids and specific ions,docs not exceed the tolerance limit for the crop. The tolerance limits for various crops are different,representing 8- to IO-foldvariation. Soil type and meteorological parameters of the site, for a given irrigationscheduling, also govern as to what win be the maximum soil solution concentration during the growth cycleof the crop. For a given crop, given soil and prevailing climate, the quality of irrigation water andmanagement ultimately determine this maximum level. At a given place, the type of soil and meteorologicalparameters cannot be managed by human beings. The farmer can, however, exercise SOme control on thequality of irrigation water by selecting an appropriate source or changing the quahty by dilution andlor hecan make certain changes in the agronomic control and crop selection. In this paper, an attempt has beenmade to describe a few more important Urigation water quality criteria which will be easy for the users tofollow and arrive at a decision on management, agronomic controls including crop selection, and search foran alternative water source of acceptable quality. This paper also describes a few cases of application of theirrigation water quality criteria in helping to make relevant decisions. 0 1999 IAWQ Published by ElsevierScience Ltd. All rights reserved

KEYWORDS

Domesticeffluents; fann management; industrialeffluents; irrigationwaterquality;salinity;sodicity,

INTRODUCTION

There are instances in India which bring out the fact that treated industrial wastewaterscan prove a boon tothe local fanners. The first example is the treated effluent from MathuraRefinery. The well waters in areasaround the refinery are highly saline and brackish. In comparison, the refinery effluent is very superior andis used by the fanners on areason either side of the effiuentchannel.Anotherexample is non-availability ofirrigation water for the farmers in areas around the Madras Refinery in Manali (Tamil Nadu). Though thefarmers are not yet aware of the fact that the treatedrefinery effluent is suitable for irrigation, this is a ready

97

98 O. D. KUCHANWAR et al.

source of irrigation water for them to tap. A third example is the areas around the proposed lignite mines atJalipa and Kapurdi in Rajasthan. In this case, the raw water for these mine areas will be transported from theIndira Gandhi Nahar Pariyojana (IGNP), about 150 km, north of these sites. The used water from theseprojects is envisaged to be acceptable for irrigation and may prove a boon to the farmers in this highly aridarea. For sustainable agriculture, however, it is necessary for the farmer to possess adequate understandingof the relationships between the irrigation water quality, quantity, soil and plant types and quality, and localmeteorology, to enable him to derive maximum benefits from various inputs continuously, and to maintainsustainability regarding the soil productivity for generations to follow.

METHODS

Irrigation water quality criteria related to domestic and industrial effluents have been described withreference to agronomic and public health aspects. A few case studies of evaluation of effluents fromdomestic and industrial establishments for irrigation have been discussed.

Agronomic aspects

The major parameters have been grouped in three categories namely salinity, sodicity and toxicity (Rhodes,1972), which may affect the soil, plant and human directly or indirectly.

By salinity of irrigation water is meant the total concentration of dissolved salts in it. When irrigation wateris applied to the soil, the total concentration increases as the water is lost through plant transpiration andevaporation. Though plants require certain elements for normal growth and absorb them as soluble saltconstituents, excessive salt concentrations are harmful (Bernstein, 1961). Plants differ widely in theirtolerance to dissolved salts. Approximately a ten-fold range in salt tolerance exists amongst them. Toleranceof some plant species to salinity of the saturated soil solution (FAD, 1976) is given in Table 1.

Table 1. Tolerance of some of the plants to salinity of the irrigation water and the soil solution (maximumpermissible limits beyond which a yield decrease of 10% may result)

ECe·, mmhos/cm CorrespondingMaximum Permissible Crops

Limit··ECw, mmhos/cm

1.5 - 3.5 1.0-2.3 Beans, carrot, onion, radish, lettuce, pepper, sweetpotato, potato, cabbage, spinach, cucumber, lemon,mosambi, cow pea. tomato, broad bean, flax, corn,groundnut

3.6 - 5.5 2.4-3.7 Musk melon, paddy, pomegranate, sudan grass, brocoli,beets, soya bean, sunflower, sugarcane, sunhemp

5.6 -7.5 3.8 -4.7 Safflower, date palm, perennial rye grass, wheat, oats,asparagus

7.6-9.5 4.8- 5.7 Sugarbeets, bermuda grass9.6 - 10.5 5.8-6.7 Cotton, barley ..

• ECe =Electncal Conductivity of the saturated soil extract In millimhos/cm•• ECw =Electrical Conductivity ofthe irrigation water

Sodicity of irrigation water may be defined as the extent of dissolved sodium that can possibly deterioratethe soil physical condition and pose infiltration and permeability problems, ultimately affecting the plantgrowth. The major criteria often used to evaluate irrigation waters from the sodicity point of view are:Sodium Adsorption Ratio (SAR) and Residual Sodium Carbonate.

Irrigation water quality and (ann management decisions

Sodium Adsotption Ratio (SAR)

The Sodium Adsorption Ratio has been defined as:

Na+

SAR = --------------------------{(Ca++ + Mg)/2}112

Where the ions are expressed in meqlL concentration in the irrigation water.

Residual Sodium Carbonate <Rsq

This is given by the relation:

99

in which the concentrations are expressed in meqlL (Wilcox, 1955). This criterion is useful in the sense thatwhen irrigation waters contain a high proportion of carbonate and bicarbonate ions, there will be a tendencyfor calcium and possibly magnesium to precipitate as carbonates when the water is concentrated bytranspiration and evaporation. This will increase the proportion of sodium dissolved in the soil water,consequently increasing the SAR ofthe resulting water.

Toxicity

This term refers to the presence of specific ions in irrigation water in concentrations which will causedefinite harm to the plants, due to uptake and accumulation of the specific constituent within the plant, andwhich may occur even though salinity is low. The toxic constituents of concern are sodium, chloride andboron.

Sodium

The aspect of deterioration of soil properties on account of soluble sodium of irrigation water is generallyrecognised. For most of the open soils with a lesser clay content, it may take a long time for deteriorationattributed to high sodium content of the water. But the plants being irrigated might absorb and accumulatesodium ions to harmful levels causing leaf bum and scorching, and the leaf tissues might die thus affectingthe plant growth. Sodium in leaf tissue in excess of 0.25 to 0.50 per cent (dry weight basis) is typical ofsodium toxicity to many crops. Most trees and woody type perennial plants are sensitive to low sodiumconcentrations. But many ofthe usual annual agrjcultural crops are not sensitive (FAO, 1976).

Chloride

Chloride is not adsorbed by soils, but moves readily with the soil water. It is taken up by plant roots andaccumulated in leaves where sensitive plant leaves exhibit the toxicity symptoms at 0.3 to 0.5 per centchloride content (dry weight basis). Most tree crops and other woody perennial plants are sensitive to lowconcentrations of chloride, while most annual crops are not. Limited data available on crop tolerance tochloride are presented in Table 2 (Rhodes & Bernstein, 1971).

Boron

Boron is essential to the normal growth ofall plants, but the quantity required is very small. A deficiency ofboron produces striking symptoms in many plant species. Boron is very toxic to certain plant species and theconcentration that will harm these sensitive plants is often approximately that required for normal growth ofvery tolerant plants. The acceptable range of concentration and tolerance of crops to boron have beenreported (Richards, 1954).

The maximum permissible values for a few important parameters in irrigation waters have been specified forspecific soil conditions and crop sensitivities as shown in Table 3.

100 O. D. KUCHANWAR et al.

Table 2. Chloride tolerances in the saturation extract ofsoil for fruit crops, rootstocks and varieties, ifleafinjury is to be avoided

Crop Rootstock or Variety Maximum permissible CI insaturation extract

meq/L

Rootstocks

Citrus Rangpur lime, Cleopatra 25(Citrus spp.) Mandarin

Rough lemon, Tangelo, sour orange IS

Sweet orange, Citrange 10

Stone fruit Marianna 25(Prunus spp.) Lovell, Shalil 10

Yunnan 7

Avocado West Indian 8(Persea americana Mill) Mexican

Grape Salt Creek 40(Vitis spp.) Dog Ridge 30

Varieties

Grape Thompson Seedless, Periette 25(Vitis spp.) Cardinal, Black rose 10

Bemes Boysenberry 10(Rubus spp.) Olallie blackberry 10

Indian Summer raspberry 5

Strawberry Lassen 8(Fragaria spp.) Shasta 5

Table 3. Suitability of irrigation water for semi-tolerant and tolerant crops in different soil types

Sr. Soil Textural Group Upper Permissible Limit ofNo

Salinity EC Sodicity SAR Sodicity RSC BoronB(micromhos/cm) (millimole/L) (meq/L) (ppm)

S.T: r' S.T: T+ S.T: r' S.T: T+

I. Above 30 percent Clay, 1500 2000 10 15 2 3 2 3Sandy Clay, Clay Loam,Silty Clay Loam, SiltyClay,Clay

2. 20-30 percent Clay, Sandy 4000 6000 IS 20 3 4 2 3Clay, Loam, Loam, Silty

Loam

3. 10-20 percent Clay, Sandy 6000 8000 20 25 4 5 2 3Loam, Loam, Silty Loam

4. Below 10 percent Clay, 8000 1000 25 30 5 6 I 2Sand, Loamy Sand, Sandy 0Loam, Silty Loam, Silt

Note: The use of waters of 4000 micromhos/cm EC and above should be confined to wmter seasoncrops only. They should not be used during the summer season. Even during emergencies not more thanone or two protective irrigations should be given to the Kharif season crops.*S.T.• Semi-tolerant crops; +T - Tolerant crops.

Irrigation water quality and farm management decisions 101

PUBLIC HEALTH ASPECTS

For constituents of public health concern in the wastewaters, specific standards still require to be developedin India. Such standards are available in the U.S. and Israel (Table 4).

Table 4. Standards for irrigation with reclaimed wastewater in Arizona.

Characteristics Crop and Landuse Category

A B C D E F G H

PH 4.5-9 4.5-9 4.5-9 4.5-9 4.5-9 4.5-9 4.5-9 4.5-9

Fecal coliforms (CFU/IOO ml) 1000 1000 1000 1000 1000 200 25 2.2Geometric mean (5 sampleminimum)

Single sample not to exceed 4000 4000 4000 4000 2500 1000 75 25

Turbidity (NTU) - - - - - - 5 1

Enteric virus (PFU/401) - - - - - - 125 1

Entamoeba hystolytica - - - - - - - ND

Ascaris lumbricoides (round - - - - - - ND NDworm eggs)

Common large tapeworm - - ND ND - - - -..CFU: Colony Fonmng Unit; NfU: Nephelometer Turbidity Unit; PFU: Plaque Fonmng Unit; ND: None

detectable. A: Orchards; B: Fibre, seed and forage crops; C: Pastures; D: Livestock watering; E: Processed foodcrops; F: Landscaped areas, restricted access; G: Landscaped areas, open access; H: Crops to beconsumed raw.

The International Reference Centre for Waste Disposal (IRCWD, 1985) recommended the following publichealth standards for use ofwastewaters for agriculture and aquaculture.

i) For restricted irrigation: ~ 1 intestinal nematode egg per litre (arithmetic mean).ii) For unrestricted irrigation: As above, plus ~ 1000 fecal colifonns/l00 ml (geometric mean).

The World Health Organisation has also recommended the above standards for use in developing countries(WHO, 1989). These can be achieved by sewage treatment through waste stabilisation ponds (Mara andPearson, 1992) or by lagooning with sufficient detention times, for example 1 month (WHO, 1989), in warmregions.

Table 5. Sewage characteristics in some towns in India"

Sr. Characteristics Nagpur Madras Madurai AhmedabadNo (Raw) (Raw) (Raw) (Treated)

(Range)Min. Max.

1. PH 7.2 6.9 7.6 7.5 7.8

2. Total dissolved solids 1400 750 2700 1105 14403. Alkalinity (as CaC03) - 133 964 584 5164. Total nitrogen 77 32 90 50 -5. Chloride 120 152 448 296 4736. BOD 5-day at 20·C 232 133 695 442 33

All values except pH expressed m mgIL.NEERIReport, 1974.

102 O. D. KUCHANWAR et al.

RESULTS AND DISCUSSION

Domestic effiuents

Characteristics of sewage effiuents show great variability in various towns in India as shown in Table 5.There may be some time during the day, that corresponds with the normal irrigation time, when the sewageis more concentrated with chloride, sulphate, dissolved solids and BOD (biochemical oxygen demand) allshowing values above the respective permissible limits. When soil conditions are favourable and the farmmanagement is geared in accordance, these characteristics can be used to benefit the crop and the soil.Conversely, when the sewage is of an acceptable quality with reference to the standards, a defectiveirrigation practice may ruin the crop as well as the soil. These points will be made clearer by studying Table6 which gives the chemical analysis of the sewage-irrigated soils of these towns.

Table 6. Analysis of sewage-irrigated soils in some towns in India"

Sr. Charactenstics Nagpur Madras Madurai AhmedabadNo.1. Waterholdingcapacity 58.08 43.7 43.16 30.02. Electrical conductivity micromhos/cm) 290 900 247 10003. pH 7.7 7.8 7.6 10.14. Total solublesalts (%) 0.09 0.28 0.079 0.325. Exchangeable Sodium 0.52 5.23 1.91 7.306. Exchangeable Potassium 0.82 0.43 2.26 0.527. Exchangeable Calcium 12.56 6.90 10.96 4.008. Exchangeable Magnesium 3.20 3.15 5.07 0.96

All valueson percentdry weightbaSIS; Exchangeable canonsexpressed as meqllOO g.• This analysisis a part of the recent surveyof sewagefarmsmadeby NEERI(NEERIReport, 1974).

The soil analysis results of Table 6 show a very high figure for exchangeable sodium, for the Madras soil.This is probably more because of a high water table in the area of excessive application rates using theconcentrated sewage than the dissolved solids or the sodium content of the sewage. The crop grown on thissoil is para grass used for fodder.

Soils at Nagpur and Madurai are reasonably well balanced as regards exchangeable sodium, potassium,calcium and magnesium. This is mostly because of the optimum conditions of irrigation management.

At Ahmedabad, even though relatively weak and dilute treated sewage is used, the high application ratesover a number of years have increased the level of the water table and consequently the sodium hasincreased to toxic levels.

Industrial effiuents

Tannery waste

Pot culture studies using a tannery effiuent revealed (Thabraj et al., 1964) that the effiuent increases theexchangeable sodium content of the soil and reduces the permeability to water and air. The excessiveamounts of sodium and chloride in this effiuent were the main sources of trouble for the plants.

Distillery wastes

Potassium is a dominant cation in this waste. If a two acre inch irrigation is given using this effiuent, the soilwill receive about 6 to 140 kg as K20 per irrigation. In normal irrigation water, the potassium content isnever so high. Though potassium is an important plant nutrient, the effect of such an excess ofpotassium onthe soil and plants has not been studied, probably because potassium is normally adequately suppliedthrough the usual potassic fertilisers. But where utilization of wastewaters as irrigants is concerned, a

Irrigat ion water quality and farm management decisions 103

standard limit or range for potassium in these waters would be most welcome. However, as regards thiseffiuent, the high values for BOD and total dissolved solids content suggest that this effiuent cannot be usedfor irrigation unless the concentration is considerably reduced by suitable treatment or dilution (Mohanrao,1971a). The wastewater can be effectively treated by a combination of anaerobic and aerobic biologicaltreatment systems. In view of the high cost of removal of total dissolved solids (TDS), dilution with suitablewater will be an ideal solution.

Dairywastes

Combined effiuent of a large dairy in this country contains, on average, 1000 mg/L dissolved solids, 112mgIL chloride, 1250 mgIL BOD and 290 mgIL oil and grease. This dairy uses its waste for crop irrigationafter dilution. The soil is loamy in character (Mohanrao, 1971a). A land area of about 122 hectares isirrigated to raise paddy, sugarcane and a variety of vegetables very successfully. Difficulties are encounteredwhen attempts are made to suitably dilute this waste for efficient use. Thus, if the BOD is to be broughtdown to 500 mgIL concentration, the waste is diluted so that the waste to water ratio is 2.3. But yet the oiland grease content would be 116 mgIL which is again more than the acceptable limit. In such cases the oilcontent can be brought down by the dissolved air flotation method to an acceptable level.

CONCLUSIONS

It is hoped that the concerned authorities, agencies and farmers will appreciate the great potential of treatedwastewaters, and manage to use them judiciously for irrigation, considering all aspects of soil conditions andplant growth,so that irrigation with domestic and industrial effiuents becomes a sustainable system.

REFERENCES

Bernstein, L. (1961) . Tolerance of Plants to Salinity. J. Irrig and Drainage Divn. Proc. Amer. Soc. OfCivil Engrs., 87 (IR-4),

1-12.Food and Agriculture Organisation of the United Nations, Rome (1976) . Water Quality for Agriculture, FAO Irrigation and

Drainage Paper No. 29.IS:11624 (1986). Guidelines for Quality ofIrrigation Water, Bureau of Indian Standards, New Delhi .International Reference Centre for Waste Disposal (IRCWD) (1985). Health Aspects of Wastewater and Excreta Use in

Agriculture and Aquaculture. The Engelberg Report .Mara, D.D. and H.W. Pearson (1992) . Sequential Batch-fed Effluent Storage Reservoirs: A New Concept of Wastewater

Treatment Prior to Unrestricted Crop Irrigations . Wat. SCI . Tech., 26(7), 1459-1464.Mohanarao, G.J. (197Ia). In: Dairy Waste Characteristics with Reference to lSI Standards. Seminar on Treatment and Disposal of

Dairy Waste , CPHERI and M.S. University, Baroda, pp.29-42.Mohanrao, G.J. (l97Ib). CPHERllntemal Report .Rhodes, J.D. (1972). Quality ofWater oflrrigation. Soil Sci ., 113(4),227-234.Rhodes, J.D. and L. Bernstein (1971) . Chemical, Physical and Biological Characteristics of Irrigation and Soil Water . In: Water

and Water Pollution Handbook, Marcel Dekker Inc., New York, Vol. I, pp.141-222 .Richards , L.A. (1954). Diagnosis and Improvement ofSaline and Alkali Soils. USDA Handbook No. 60.Thabaraj, G.J., Bose, S.M. and Nayudamma, Y. (1964). Utilization of Tannery Effluents for Agricultural Purposes . Env. Hlth.,

Vol. VI, No.1, 18-36.WHO (1989). Health Guidelines for the Use of Wastewater in Aquculture and Aquaculture. Technical Report Series 778, WHO

Geneva.Wilcox, L.V. (1955) . Classification and Use ofIrrigation Waters. USDA Circular No. 969.