changes in soil fertility parameters in response to irrigation of …mrusan/changes in soil...

COMMUNICATIONS IN SOIL SCIENCE AND PLANt' ANALY:Sl;)

Vol. 34, Nos. 9 & 10, pp. 1281-1294,2003

Changes in Soil Fertility Parameters in Responseto Irrigation of Forage Crops with Secondary

Treated Waste,yater

lVlunir J. lVlohammad1,*and N. I\tlazahreh2

[Department of Natural Resources and the Environment.Faculty of Agriculture, Jordan University of Science and

Technology (JUST), Irbid, Jordan2National Center for Agricultural Research and Technology

Transfer, Baqa'a, Jordan

ABSTRA CT

Field experiments were conducted to evaluate the effect of irrigation withtreated wastewater on soil fertility and chemical characteristics. Threefield experiments were conducted at a farmer's field near RamthaWastewater Treatment Plant. Corn (Zea mays) was planted for twoseasons as a summer crop while vetch (Vicia saliva) for one season as awinter crop.

Plots were irrigated with either potable water (PW) or wastewater(WW) in amount according to the following treatments: i) potable water

*Correspondence: Jvlunir 1. Mohammad, Department of Natural Resources and theEnvironment, Faculty of Agriculture, Jordan University of Science and Technology(JUST), P.O. Box 3030, Irbid, Jordan; Fax: 962-2-7095069; E-mail: [email protected].

1281

DOl: 10.1081/CSS-120020444

Copyright @ 2003 by Marcel Dekker, Inc.0010-3624 (Print); 1532-2416 (Online)

www.dekker.com

1282 Mohammad and Mazahreh

equivalent to 100% class A pan reading (P\V); ii) wastewater equivalentto 100% class A pan reading (WWI); iii) PW with application fertilizerequivalent to Nand P content of WW (PWF) and iv) wastewaterequivalent to 125% class A pan reading (WW2). Treatments werereplicated 4 times in a randomized complete block design. Soil sampleswere taken before and at the end of the growing season and were analyzedfor soil parameters. WW samples were taken and analyzed periodicallyfor major characteristics. WW analysis indicates inefficient treatment andhigh values of Biological Oxygen Demand, salt content and reduced formof nitrogen. The results of the field experiments indicate that WWirrigation decreased soil pH and increased soil salinity, soil phosphorus(P), potassium (K), iron (Fe), and manganese (Mn) levels. Soil organicmatter increased only in the topsoil and by the highest rate of WWirrigation. This effect could be attributed either directly through theaddition of the nutrients and organic compounds to the soil or indirectlythrough enhancing solubility of soil nutrients. Soil zinc (Zn) and copper(Cu) were not significantly affected by W\V irrigation. It can beconcluded that secondary treated WW can improve soil fertilityparameters, however, more efficient treatment is recommended to reducesalt content. In addition, proper irrigation management and periodicmonitoring of soil quality parameters are required to minimize adverseeffect on the soil.

Key Words: \Vastewater; Soil pH; Soil salinity; Soil macro andmicronutrients.

INTR 0 DUCT! 0 N

The demand for water is continuously increasing in arid and semi aridcountriesJ1J Therefore, water of higher quality is preserved for drinkingpurposes while that of lower quality is recommended for irrigation. [2]Municipal wastewater is less expensive and considered an attractive source ofirrigation water in these countries. [3] Therefore, the interest in reusingwastewater for irrigation is rapidly growing in most countries. Moreover,irrigation with municipal wastewater is considered an environmentally soundwastewater disposal practice that helps in minimizing the pollution of theecosystem subjected to contamination by direct disposal of wastewater intosurface or ground waterJ4] In addition, wastewater is a valuable source for'-plant nutrients and organic matter needed for maintaining fertility andproductivity of arid soils.fS]However reuse of waste water for irrigation maypoten'tial1y create environmental prt)blems if not properly treated andmanaged.f6,71

Irrigation with Secondary Treated Wastewater 1283

When wastewater is used continuously as the sole source of irrigationwater for field crops in arid regions, excessive amounts of nutrients weresimultaneously applied where their accumulation in the soil may causeunfavorable effects on productivity and quality of crops and soil. [8,9]Therefore, management of irrigation with wastewater should consider thenutrient content in relation to the specific crop requirements and levels of plantnutrients in the soil and other soil fertility parameters.

In Mediterranean countries such as Jordan, there is an increasing andurgent need to conserve and protect water resources. Water is a vital resourcebut a severely limited one in these countries. Consequently the reuse ofwastewater for agriculture is highly encouraged. [1,10]In Jordan, for example,the available amount of wastewater is expected to reach up to 150 MCIvI in2010[11] and most of this water has undergone secondary treatment. [12]Thisrelatively large quantity of wastewater has a substantial fertilizer value and is apotential for useful irrigation water. [13-15] Secondary treated wastewaterusually contains essential plant nutrients such as N, P, K and micronutrients.On the other hand, wastewater may also contain pathogens, toxic chemicalsubstances above acceptable levels and plant nutrients in excess of croprequirements.[4] Consequently, reuse of wastewater for irrigation can lead toaccumulation of these substances in the soils thus affecting their fertility andproducti vi ty .

The majority of the research conducted on wastewater reuse in agricul turefocuses mainly on its effect on plant growth and development with littleattention to the changes induced in the soil fertility and chemistry parameters.The objectives of this study were to evaluate the fertility and chemical soilcharacteristics and the possible accumulation of heavy metals in these soils, inresponse to irrigation of forage crops with treated wastewater.

lVIATERIALS AND METHODS

Three field experiments were conducted at a farmer's field located nearthe Ramtha Treatment Plant in a soil that had never been previously irrigated.Two sources of irrigation water were used to irrigate vetch (Vicia sativa) andcorn (Zea mays). Potable well water (PW) and secondary treated municipalwastewater (WW), from the Ramtha Waste water Treatment Plant in Ramtha,Jordan, were used. Plots were irrigated with either potable water (PW) orwastewater (WVV)in amount according to the following treatments: i) PWequivalent to 100% class A pan evaporation reading (as taken periodicallyfrom the nearest Meteorological Weather Station) that estimates the waterrequirement of the crops ii); PWF which is PW plus an application of fertilizer


equivalent to Nand P contents ofW\V1 iii); WW1 equivalent to 100% class Apan reading and iv) \VW2 equivalent to 125% class A pan reading. Irrigationin the WW2 was sufficient to ensure that soilleachate percolated beneath theroot zone to leach out any possible accumulation of salts contained in the WW.A leaching fraction of approximately 25% was maintained for WW2 treatmentthrough out the study. All treatments were replicated 4 times in a randomizedcomplete block design (RCBD).

Nitrogen and P were not applied to the soil except for one treatment(PWF) as designed by the experiment. For this treatment, N was added asammonium sulfate and P as triple superphosphate. Both Nand P fertilizerswere broadcasted into the soil surface before each irrigation at a rateequivalent to their content in the amount wastewater used for the sameirrigation as estimated from the class A pan reading.

The corn crop was planted as a summer crop for two seasons and vetch asa winter crop for one season. In the first season the corn was,planted in May1994 and harvested,in August 1994 followed by vetch planted on February1995 and harvested in May 1995. Then corn was planted again in the sameplots in May, 1995 and harvested in August, 1995. Corn was planted in rows,75 cm between rows and 25 cm between plants at a depth of 6 cm. The plotdimensions were 3.75 X 3111,with five rows of plants in each plot. Vetch wasplanted at a rate of 120 kg ha- 1

The irrigation \vater was delivered through a closed irrigation lines to theexperimental plots where the water was distributed unifonnly. A water meterwas installed in the irrigation system for monitoring the amount of irrigationwater to be applied. The crops were irrigated twice a week for the summercorn crop and once a week (except during the rainy periods) for the wintervetch crop.

Soil Sampling and Analysis

Before seeding, composite soil samples were taken to a depth of 1.2 m

from each block. At the end of the growing seasons, composite soil sampleswere from a depth of 0.30 and 0.6 m from each plot. Samples were air dried,grounded to pass 2 mm sieve. Soil samples were then analyzed for pH and forelectrical conductivity (EC) in the saturation paste;[J6] for total Kjeldahl:nitrogen[I7]; for phosphorus by extraction with 0.5 M NaHCO3[18];for CaCO3 .

by acid neutralization method[J9]; for exchangeable K by extrac60n with 1M .

NH4Oac[20];for cation exchange capacity (CEC) by the method described byPolemio and Rhoades[2J] and for soil texture by hydrometer methodJ22] Soil ;

organic matter was measured by rapid oxidation, [23]and Fe, Zn, Cu, and Mn .


Table 1. Selected characteristics of soil at the experimental site.

by extractions with DTP A. [~41Selected soil characteristics are presented inTable 1.

Water Sampling and Analysis

Wastewater samples were analyzed weekly for physical and chemicalvariables. The average values over the study period are reported in Table 2.The potable well water samples were analyzed once per season and theaverage values of the study period are also shown in Table 2. Irrigation watersamples were analyzed according to the American Public Health Association(APHA). [25]

-

Statistical Analysis

Analysis of variance (ANOVA) was used to determine the effect of eachtreatment. When the F ratio was significant a multiple mean comparison wasperformed using Fisher's Least Significance Test (0.05 probability level).Statistical analyses were performed with SYSTAT Statistical Program. [26]

RESUL TS AND DISCUSSION

The amount of irrigation water applied to crops was as follows: 540 mmand 675 mm of treated wastewater for the W"VI and WW2 for the corn grown'-'

in 1994 season. The potable water for each of the PW and PWF treatments wasapplied in amount of 540 which is equivalent to the amount applied to theWWl treatment. For the corn grown in the 1995 season, the amount of potable

Soil CEC

depth ECa aNI CaCO3 P (mg K(mg (cmol(cm) pH (dS m-I) (%) (%) kg-I) kg-I) kg-I) Texture

0-30 7.8 0.8 0.48 12.2 5.2 537.6 32.1 Clay30-60 7.7 0.6 0.34 15.2 4.3 438.6 29.1 Clay60-90 7.7 0.6 - 15.2 2.5 401.5 28.4 Clay90-120 7.8 0.8 - 14.8 1.9 413.9 24.5 Clay

a EC = electrical conducti'v'ity;OM = organic matter.


'TDS = total dissolved solids; BOD = biologicaloxv~en demand: ND = nondetectable.

~ -

water and treated.wastewater applied for the treatments P\V, PWF, WWl, andWW2 were 615 mm, 615 mm, 615 mm, and 769 mm, respectively. The vetchcrop grown in the 1994 winter season received 74 mm, 74 mm, 74 mm, and93 mm for the P\V, P\VF, WWl, and v.lW2 treatments, respectively. Duringthe rainy periods irrigation water was not applied. Therefore, vetch as a wintercrop received relatively less irrigation water as supplemental irrigation.

Irrigation '" ater Characteristics

The wastewater used for irrigation is alkaline with pH value of 7.56 andsaline with an average content of total dissolved solids (TDS) of 1225 mg L-](Table 2). The wastewater contains much higher ammonium compared tonitrate concentration (Table 2) indicating inefficient effluent treatment andincomplete nitrification. [27.28]The inefficient and incomplete oxidation ofeffluent is also evidenced by high values of biological oxygen demand BaD(Table 2). On the other hand, the higher contents of ammonium, nitrate and

Table 2. Characteristics of the potable and second-ary treated wastewater used for irrigation (meanvalues over the study period).

Parameters Secondary treated(m aka-I) wastewater Potable water

pH (unit) 7.56 7.9TDS 1225 650BOD5 290 ND

PO4 49 0.03

NH4 118 ND

NO3 2.9 59Cl 586 262Fe 0.14 NDMn 0.07 NDCu ND NDZn 0.03 NDCd 0.04 NDCr 0.01 NDNi ND NDPb 0.02 ND


phosphate compared to potable water are considered a good source of plantnutrients for improving soil fertility and productivity. Concentrations of heavymetals in the wastewater are higher than in the potable water but remainedlower than the recommendedinaximum levels in irri2ation water. However," ~

their danger is associated with: possible accumulation in soil and plants withcontinuous use of wastewater in irrigating the same fields. Therefore, theyshould be periodically monitored in the soil and plants.

Soil Characteristics

Soil pH at the end of the growing season was significantly lower for bothrates of wastewater application compared to both rates of potable watertreatments (Table 3). The high content of ammonium in the wastewaterresulted in its accumulation in the soil. Nitrification of this ammonium would

serve as a source of hydrogen ions which may lead to the decrease in the soilpH.[9,29]Although this decrease in the soil pH might not persist longer due tothe higher buffering capacity of this highly calcareous alkaline soil and the soilpH is expected to rise again/91 the crops would probably benefit from this

Means with different letters within rows are significantly different (p < 0.05).a PW = potable water; PWF potable water with fertilizer added; WW 1andWW2 = lowest and highest wastewater application rates respectively.

Table 3. Soil characteristics of the soil irrigated with potable and wastewater at theend of the study period (% for Nand mg kg -1 for other nutrients).

Treatmentsa

Parameters ..Soil depth, cm PW PWF WvVl vVW2

pH 0-30 7.71 a 7.73 a 7.56 b 7.51 b30-60 7.80 a 7.82 a 7.70 a 7.80 b

EC, dS m-I 0-30 0.81 a 0.82 a 1.8 b 1.6 b30-60 0.95 a 0.94 a 1.6 a '2.0 b

OM, % 0-30 0.51 a 0.55 a 0.6 a 0.73 b30-60 0.50 a 0.49 a 0.54 a 0.56 a

N 0-30 0.07 a 0.06 a 0.06 a 0.07 a30-60 0.05 a 0.05 a 0.06 a 0.06 a

P 0-30 4.3 a 4.9 a 9.3 b 9.9 b(NaHCO3-P) 30-60 3.5 a 4.0 a 9.1 b 9.2 bK 0-30 541 a 533 a 581 a 583 a(OAc-K) 30-60 502 a 540 a 638 b 653 b


temporal decrease in soil pH during the growing season. Such decrease in thesoil pH would enhance solubility and availability of certain nutrients inc:t1careous soils such as phosphorus, Fe~ Mn, Zn, and CU.[30,31]Soil pH wasalso reported to increase following long term wastewater application[32] wherethe authors attributed this increase to the chemistry and high content of basiccations such as Na, Ca, and Mg in the wastewater applied for a long period.

Wastewater irrigation resulted in significantly higher values for electricalconductivity (EC) of the soil saturation extract compared to soil irrigated withpotable water (Table 3). The increase in EC is mainly attributed to the originalhigh level of TDS of the wastewater that would accumulate in the soil withcontinuous wastewater application. Potable water, unlike wastewater, did notincrease the original EC of the soil. Other researchers reported similar increasein the soil EC by wastewater irrigation, [9,33]but contrary to our results theyobserved an increase in the soil EC even by irrigation with potable waterwhich caused a less increase in the soil EC compared to the wastewaterirrigated soil.[34]Both potable water and potable water with the addition offertilizer had similar effect on soil salinity. The lower rate of wastewaterapplication (W\VI) increased salinity more in the topsoil while the higher rate(\VV.,r2)in the subsoil. The accumulation of salts in the topsoil more than in thesubsoil ilTigated with the lower wastewater rate is probably related toevaporation effect and absence of the leaching fraction. The subsoil on theother hand, contained higher salt concentration when soil was irrigated by thehigher rate of water application which was probably caused by moving saltsdeeper into the subsoil by the leaching fraction. [35]The continuous bund up ofsalts in the soil surface may adversely affect seed germination, seedlingestablishment and plant growth and may also deteriorate soil productivhy.[4]Increased salinity may also negatively affect activity of the phosphataseenzyme and soil microorganismsl33] which will be negatively reflected on soilproductivity. Therefore, addition of the leaching fraction to the irrigationrequirement should be considered when wastewater is used for irrigation.. Soil organic matter was not affected by potable water treatments nor bywastewater irrigation treatments (Table 3) except by the higher rate ofwastewater application which resulted in higher soil organic matter in the topsoil, but not in the subsoil (Table 3). Vazquezmontiel et al.[9]found no positiveeffect on change in soil organic matter with wastewater irrigation, while otherresearchers reported an increase in the soil organic matter followingwastewater irrigationJ34] The soil organic matter in this study was notincreased by lower rate of wastewater irrigation which can be partiallyattributed to the possible decomposition and oxidation of the soil carbontoward the end of the growing season by the introduced microorganisIlls bywastewater. .

Irrigation with Secondary Treated \Vastewater l.l(s~

Soil Nitrogen, Phosphorus, and lVlicronutrients

Both rates of wastewater increased levels of N, P, K, Fe and Mn in thesoil, but not Cu and Zn (Tables 3 and 4). Neither potable water treatmentsignificantly increased any of these plant nutrients. The increase in soil N, P,and K contents with wastewater application can be attributed to their highcontent in the wastewater used (Table 2). On the other hand, although thewastewater contained very small amount of micronutrients, the DTP Aextractable Fe and Mn significantly increased in the soil. This could beattributed to the chelation reactions of Fe and Mn with the organic compoundsprovided by wastewater application, which is considered one of the mainmechanisms for enhancing solubility and availability of Fe and Nln in alkalineand highly calcareous soils. [30]In addition, both Fe and NIn are transitionalmetals that can easily change their oxidation states. The possible reducingconditions created during irrigation periods with wastewater can facilitatereduction of both Fe and Mn into the more soluble and available reduced

forms. An evidence of reducing condition created by wastewater applicationcan be considered through the enhanced denitrification with wastewater

application observed by~.Schipper et al.[32] Both rates of wastewaterapplication had similar effect on these soil parameters indicating that

:Nleans with different letters within rows are significantlydifferent (p < 0.05).a PW = potable water; PWF = potable water with fertilizeradded; WW 1and WW2 = lowest and highest wastewaterapplication rates, respectively.

Table 4. DTPA extractable mlcronutrients and heavymetals in the soil (top 30 cm) irrigated with potable andwastewater at the end of the growing season (mgkg-I).

Treatmentsa

Parameters PW PWF WWl WW2

Fe 4.5 a 4.3 a 5.9 b 6.4 bMn 5.8 a 5.9 a 7.8 b 8.1 bCu 1.6 a 1.5 a 1.5 a 1.6 aZn 1.8 a 1.8 a 1.9 a 2.0 aCd 0.12 a 0.11 a 0.09 a 0.23 aCr 0.01 a 0.03 a 0.03 a 0.02 aNi 0.52 a 0.55 a 0.44 a 0.48 aPb 0.82 a 0.79 a 0.89 a 0.91 a


the threshold rate necessary to change these soil paran1eters would be lowerthan or equal to the lowest rate. [32]

Other researchers found that application of wastewater irrigation resultedin additions of N, P, K at about 4, 10, and 8 times, respectively, therecomn1ended fertilizer rates for forage crops. [36]Monnett et al.[37]found thatnitrogen and phosphorus removal by wastewater-irrigated crops were 90% and96%, respectively. On the contrary, Schipper et al.[32]found that total Nandtotal C were not affected by irrigation with either wastewater or potable water.The variation in these results is mainly attributed to the different chemicalcharacteristics of wastewater used, type of soil, and crops involved andirrigation management adopted. Therefore, it is highly recommended that allthese factors be considered when the rate of wastewater application isdetermined.

The concentrations of the DTPA extractable heavy metals such ascadmium (Cd), chromium (Cr), nickel (Ni), and lead (Pb) in the soil after cropharvest were not affected significantly by the irrigation water source. Thiscould be attributed to their very low concentrations in the irrigation water. Inaddition, fine textured soils have the capacity to treat wastewater and retainconsiderable amount of heavy metals rendering them not bioavailable thatcommonly measured by DTPA extraction. It has been reported that thetreatment capacity of the soil is somewhat fixed and is determined by thephysical chemical properties of soil and by cropping system. [38]The soil of ourexperimental site has a fine texture and a high CEC, therefore, high retentioncapacity for elements and microorganisms delivered by wastewater irrigationis expected. However, improper (such as overirrigation) application and/orlong term application of wastewater may lead to nutrient imbalance, toxicityproblems by heavy metals, and soil deterioration or reduction on the soilproductivity. Therefore, periodic monitoring of their concentrations in the soilis highly recommended because of the possible accumulation in the soil aftercontinuous wastewater application. In addition, the possible increase in thesolubility of the indigenous insoluble heavy metals ia the soil as a result of thechelation or acidification action of the applied wastewater irrigation has alsobeen reported. [4]

CONCLUSIONS

vV'astewater application has significant impact on chemical and fertility

parameters of the soil. Therefore, characteristics of wastewater and soil shouldbe considered, in management of wastewater irrigation projects. Based on theresults of this study, it can also be concluded that continuous application of


waste water may lead to soil accumulation of plant nutrients and heavy metalsbeyond crop removal causing a nutrient imbalance in the soil. In addition,seasonal irrigation with wastewater leads to the accumulation of salts in thesoil and leaching fraction should be considered to leach out the salts beneaththe root zone. On the other hand, wastewater irrigation if properly managedcan enhance soil fertility and productivity of the soil through increadng levelsof plant nutrients and soil organic matter. Finally, proper management ofwastewater irrigation and periodic monitoring of soil fertility and qualityparameters are required to ensure successful, safe and long term reuse ofwaste water for irrigation.

ACKNOWLEDGJ\tIENTS

This study was funded partially by the National Center for AgriculturalResearch and Technology Transfer and by the Research Deanship of JordanUniversity of Science and Technology.

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