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Journal of Cleaner Production 52 (2013) 474e480

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Journal of Cleaner Production

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Nitrate retention and physiological adjustment of maize to soilamendment with superabsorbent polymers

A. Egrinya Eneji a,*, Robiul Islam b, P. An c, U.C. Amalu a

aDepartment of Soil Science, University of Calabar, NigeriabDepartment of Agronomy and Agricultural Extension, Rajshahi University, Rajshahi 6205, Bangladeshc Laboratory of Plant Ecophysiology, Arid Land Research Center, Tottori University, Japan

a r t i c l e i n f o

Article history:Received 12 October 2012Received in revised form14 February 2013Accepted 21 February 2013Available online 21 March 2013

Keywords:Stress physiologyIrrigationMaizeNitrate leachingDrought stressSuperabsorbent polymer

* Corresponding author.E-mail address: aeeneji@yahoo.co.uk (A. Egrinya E

0959-6526/$ e see front matter � 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.jclepro.2013.02.027

a b s t r a c t

Underground water pollution associated with nitrate leaching has become a major concern in areas withintensive cereal production; in areas with dry climates, water scarcity is the main limitation to cropproduction. We thus hypothesized that use of super absorbent polymers (SAP) may effectively increasenitrogen use efficiency by minimizing leaching and enhancing water and nitrate retention in the soil.Here, we evaluated nitrate movement in soils amended with SAP and determined changes in maizegrowth based on enzyme activities and physiological parameters. Nitrate retention was studied in sixundisturbed soil lysimeters under different fertilizer (standard, medium or 75% and low, or 50% ofstandard) rates with (30 kg/ha) or without SAP. Maize yield decreased 20% under medium and 38% underlow fertilizer rates but SAP application increased yield (P < 0.05) by 44% at medium and 80.3% at lowfertilizer levels. Use of SAP plus only half the standard fertilizer rate (150 kg urea, and 33 kg each ofsuperphosphate and potassium sulphate) minimized nitrate leaching and enhanced uptake with littlechange in yield relative to the standard fertilizer rate. On the evaluation of SAP at three irrigation levels(adequate, moderate and deficit), we found that the relative water content (RWC) and leaf waterpotential (j1) were much higher in plants treated with SAP and under deficit irrigation, the SAPincreased maize biomass by 99% compared with only 11% under adequate irrigation and 39% undermoderate irrigation. Plants treated with SAP under deficit irrigation showed reduced stress signals basedon the superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX) andglutathione reductase (GR) activities in leaves. The improved growth of maize treated with SAP underdeficit irrigation was ascribed to maintenance of higher RWC, intercellular carbon dioxide concentrationand net photosynthetic and transpiration rates.

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1. Introduction

The ever increasing rate of inorganic fertilizer use in modernagricultural production has raised quite some concern aboutenvironmental safety and sustainability. Some studies (e.g. Yuanet al. 1995; Zhu and Chen, 2002; Li and Li, 2000) have shown thatmuch of the excessively applied fertilizer was lost through leaching,resulting to serious environmental hazards, including soil acidifi-cation, heavy metal contamination and greenhouse gas emission.Nitrate leaching and the resulting ground water contaminationare related to N fertilizer use in agricultural land worldwide(Ibnoussina et al., 2006). Although necessary for profitable cereal

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production, excessive use of N fertilizer may have adverse effects ongroundwater quality (Schepers et al., 1991); much of the nitrogenleached from soil is in nitrate form and the leaching losses wereinfluenced by the amount applied (Brandi-Dohrn et al., 1997;Owens et al., 1999; Kuo et al., 2001; Ibnoussina et al., 2006). In somecountries like China, overuse of N fertilizer has caused a decline inpH and soil acidification far in excess of that caused by acid rain(Zhao et al., 2010). Thus, the challenge is to develop timely andviable alternative soil-water-crop management system to mitigatethe worsening trends in environmental degradation and agricul-tural productivity.

Use of water-saving super absorbent polymers (SAP) may be aneffective way to increase nutrient use efficiency in crops (Lentz andSojka, 1994; Lentz et al., 1998). When polymers are incorporatedwith soil, they presumably retain large quantities of nutrients,which are released as required by the plant. Thus, plant growth

Fig. 1. Schematic diagram of the lysimeter showing the six sampling points.

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could be improvedwith limitedwater and nutrient supply (Gehringand Lewis, 1980). The incorporation of superabsorbent polymerwith soil improved soil physical properties (El-Amir et al., 1993),enhanced seed germination and emergence (Azzam, 1983) andcrop growth and yield (Yazdani et al., 2007) and reduced the irri-gation requirement of plants (Blodgett et al., 1993; Taylor andHalfacre, 1986). The use of hydrophilic polymer materials as car-rier and regulator of nutrient release was helpful in reducing un-desired fertilizer losses, while sustaining vigorous plant growth(Mikkelsen, 1994).

More than any other factor, drought stress severely limits cropgrowth and productivity (Todorov et al., 1998). Drought can resultin the closure of stomata and increased biosynthesis of the stresshormone, abscisic acid (ABA), as well as the induction of droughtand ABA-responsive genes. Efficient management of soil moistureis therefore important for agricultural production in areas withscarce water resources. Drought stress invariably leads to oxidativestress in the plant cell due to higher leakage of electrons toward O2during photosynthetic and respiratory processes leading to exces-sive production of reactive oxygen species (ROS) (Asada, 1999). TheROS such as O�

2 , H2O2 and OH radicals have potential to interactwith many cellular components, causing significant damage tomembrane and other cellular structures, and consequently growthinhibition (Blum, 1996). Some of the ROS are highly toxic and mustbe detoxified by cellular responses if the plant is to survive andgrow (Drame et al., 2007). The ROS scavenging depends on thedetoxification mechanism, which may occur as a result of sequen-tial and simultaneous action of a number of antioxidant enzymes,including superoxide dismutase (SOD), catalase (CAT), peroxidase(POD), ascorbate peroxidase (APX) and glutathione reductase (GR).

The amelioration of drought stress by SAP has been confirmed inseveral studies (Blodgett et al., 1993; Gehring and Lewis, 1980;Islam et al., 2009; Yazdani et al., 2007). The SAP improved theporosity, structure and water-holding of the soil (El-Amir et al.,1993; Karimi et al., 2009). Also, the use of hydrophilic polymermaterials as carrier and regulator of nutrient release minimizedundesired fertilizer losses and sustained considerable plant growth(Mikkelsen, 1994; Tong et al., 2009). However, much of these re-ports were not based on research conducted in the field and werepoorly related to intrinsic plant function. In this study, we deter-mined nitrate retention in soils following an amendment with SAPand the associated changes in maize growth at the physiologicallevel.

2. Materials and methods

2.1. Experimental sites

The experiments were performed at the National ExperimentalStation for Precision Agriculture, Xiaotangshan and China Agricul-tural University, Beijing (40�100 N, 116�270 E), China.

2.1.1. Experiment 1: nitrate retentionExperiment 1 was conducted on a loamy sand of which the top

(0e20 cm) layer contained 63% sand, 20% silt and 17% clay with abulk density of 1.39 g cm3. The total N content was 86 g kg�1 andavailable P and Kwere (mg/kg) 21.5 and 83.5 respectively. Thirty sixlarge, undisturbed soil monolith lysimeters (35 cm in diameter and150 cm in depth with a surface area of 55 cm2) made of polyvinylchloride (PVC) cylinders were used. The preparation and installa-tion of the lysimeters were described in Islam et al. (2009).Leachates were collected from each lysimeter into plastic con-tainers, which were connected through a flexible plastic tube to thedrainage outlet at the basal cap of each lysimeter. Each lysimetercontained 6 holes located 30, 50, 70, 90 and 110 cm from the top to

access TDR probe andmonitor soil nutrient status (Fig. 1). The holeswere sealed with rubber stopper after each measurement.

Super absorbent polymer (granular) was applied to the soil in thelysimeter up to the 20 cm depth during seed sowing at 30 kg ha �1;the control lysimeter received only fertilizer and no SAP. Standardapplication rates (ha�1) of inorganic fertilizer for the experimentalarea was 300 kg urea (N), and 100 kg each of superphosphate (P)and potassium sulphate (K) (Li and Li, 2000). We used threefertilizer application levels (standard rate, 75% of standard rate ormedium rate and 50% of standard rate or low rate). Thus, there weresix treatment combinations of two SAP application rates and threefertilizer regimes. The treatments were replicated four times andarranged into a completely randomized design. Jing Dan 28, acommonly grown corn variety (Zea mays L.) in the north China plainwas used for the experiment. Seeds were directly sown into thelysimeter and after emergence, seedlings were thinned to 1 standper lysimeter (Fig. 2).

Nitrogen (urea, 46% N) was split into base and dressing appli-cations, and phosphorus (superphosphate, 5.2% P) and potassium(potassium sulphate, 41.4% K) fertilizers were applied as base fer-tilizer. Irrigation was applied immediately after the N applicationaccording to standard practices in the region. Total irrigation was60 mm in three spells which was maintained by observing droughtstatus and plant requirements.

Maize growth (plant height, leaf area, grain yield and biomassaccumulation) was monitored. Harvested samples were oven-driedfor grain yield and biomass determination. The (1000) grain weightwas calculated from randomly sampled grains after harvest. Har-vest index was calculated as the ratio of grain yield to shootbiomass. Leachate samples were collected at 7 days interval. Thevolume of leachate was recorded for each lysimeter and a sub-sample of 10 mL was immediately filtered and stored at 4 �C until

Fig. 3. A. Negative hydraulic pressure controlled auto-irrigation device and B.magnified view of water-supplying micro porous ceramic plate (WS, water supplyingtube; PAP, pressure adjusting pipe; WR, water reserving tube; AI, air inlet; NPCS,negative pressure controlling system; CP, ceramic plate).

Fig. 2. Young maize plants growing inside the buried lysimeters.

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analysis. Nitrate-N was determined using the UV spectrophoto-metric screening method (APHA, 1995). The total NO3eN leachinglosses were calculated based on NO3eN concentrations in theleachate collected from each lysimeter and the volume of totaldrainage.

2.2. Statistical analysis

An analysis of variance was performed using the STATEVIEWsoftware to statistically partition the effect of superabsorbentpolymer rate and fertilizer. Treatment means were compared usingthe Fisher’s protected least significant differences (LSD) at the 5%level of probability.

2.2.1. Experiment 2: ecophysiological studiesThe study was conducted in the greenhouse using a near neutral

(pH 7.3) sandy loam soil containing 512 g kg�1 sand, 12.2 g kg�1

organic carbon, 1.08 g kg�1 total nitrogen, 0.044 g kg�1 available Pand 0.087 g kg �1 available K. Fifteen kilograms of the air-dried,free-draining soil with recommended compound fertilizer werefilled into plastic pots (height, 30 cm; diameter, 25 cm) and the SAPwas applied at 30 kg ha �1. The control pots received only com-pound granular fertilizer (NPK 15:15:15). The maize cultivar, Hua-niang 10, was sown in the pots inside a semi-underground, semi-arched (70% of light transmission) and lit plastic-covered green-housewith air temperatures controlled between 22 and 28 �C usingan evaporative air cooler.

Three irrigation regimes (adequate, moderate and deficit) wereimposed using a negative hydraulic pressure controlled auto-irrigator (Xue et al. 2005, Fig. 3). For this study we created acontinuous flow of water at P-3, P-6 and P-9 kPa (P being equivalentto the flow under normal atmospheric pressure). For propergermination and seedling growth, an optimum flow of water wasmaintained for the first two weeks in all treatments.

2.3. Data collection

Determination of relative water content (RWC), leaf water po-tential (jl), lipid peroxidation, antioxidant enzymatic activities andsoluble protein content was done at 7 weeks after sowing (WAS).Relative water content (RWC) of leaves was determined accordingto Barr and Weatherley (1962). Leaf water potential (jl) wasmeasured around mid-day (11: 30e13: 00), on fully expandedleaves using a pressure chamber (Model 1000; PMS, Albany, OR,USA). Data on shoot and root dry mass were obtained at 8 WAS.

Lipid peroxidation was estimated from the level of malondial-dehyde (MDA) production using thiobarbituric acid (TBA) accordingto Sairam and Srivastava (2001). Fresh leaf (0.5 g) was homogenizedin 5mL of 0.1% trichloroacetic acid (TCA) and centrifuged at 10000 gfor 10 min. The mixture containing 1 mL sample supernatant, 4 mL20% TCA and 0.5% TBA was heated at 95 �C for 30 min, quicklycooled and centrifuged at 10000 g for 10 min. The resultingsupernatant was used for spectrophotometric determination ofMDA. Absorbance of þTBA was read at 532 and 600 nm using thecorresponding eTBA as the blank. The MDA concentrations werecalculated according to Du and Bramlage (1992).

Total soluble protein was extracted from 0.5 g leaf tissue in 5 mL0.1 M TriseHCl (pH 7.5) containing 50 mM ascorbic acid, 1%b-mercaptoethanol and 1 mM phenylmethylsulfonyl fluoride aftercentrifugation (15000 g for 30 min) at 4 �C. Protein content wasdetermined using bovine serum albumin as standard (Jiang andHuang, 2002).

To determine enzyme activities, frozen leaf tissues (0.5 g) werehomogenized at 4 �C in 5 mL of 0.05 M sodium phosphate buffer(pH 7.0). Extracts were centrifuged at 15000 g for 30 min and thesupernatants were used for the assays of enzyme activities. Su-peroxide dismutase (SOD) activity was determined according toSarkar et al. (2001) using the photochemical nitrobluetetrazolium(NBT). One unit of SOD is defined as being present in the volume ofextract that causes inhibition of the photo reduction of NBT by 50%.Catalase (CAT) activity was estimated by monitoring the initial rateof disappearance of H2O2 at 240 nm (E ¼ 39.4 mM�1 cm�1) for 30 saccording to the method of Sairam and Srivastava (2001). The re-actionmixture contained 50mM sodium phosphate buffer (pH 7.0),15 mM H2O2 and crude enzyme extract. Peroxidase (POD) activitywas determined by recording the oxidation of guaiacol in thepresence of H2O2. The increase in absorbance was recorded at470 nm (Hernandez et al., 2000). The reaction mixture contained100 mL crude enzyme, 500 mL H2O2, 500 mL guaiacol and 1900 mLpotassium phosphate buffer (pH 6.1). Ascorbate peroxidase (APX)activity was measured following the procedure described in Kuk

Table 1Plant height, leaf area, stem diameter, number of grains per plant and 1000 grain weight of corn under different fertilizer and superabsorbent polymer (SAP) treatments.

Treatments Plantheight (cm)

Leafarea (m2)

Stemdiameter (cm)

No. grains/plant

Biomass(t/ha)

Harvestindex

Grain yield(t/ha)

1000 grainweight (g)

Fertilizer rate (F)Standard 185.8 � 5.5 0.50 � 0.14 1.91 � 0.043 400.7 � 10.6 32.3 � 1.0 0.32 10. 4 � 0.3 240.9 � 4.6Medium 163.2 � 4.8 0.43 � 0.12 1.77 � 0.055 382.5 � 10.8 29.0 � 1.4 0.30 8.6 � 0.21 225.8 � 6.5Low 152.3 � 5.1 0.39 � 0.14 1.71 � 0.044 349.3 � 10.2 23.0 � 1.6 0.28 6.5 � 0.26 207.6 � 5.5

SAP (S)Without 151.8 � 4.9 0.39 � 0.15 1.66 � 0.043 341.5 � 9.7 22.2 � 1.0 0.35 7.7 � 0.24 211.2 � 6.8With 183.5 � 5.5 0.48 � 0.16 1.96 � 0.037 409.4 � 9.8 34.5 � 1.7 0.32 10.9 � 0.23 240.8 � 4.6

LSD (0.05) 10.66 0.025 0.088 19.85 2.1 0.07 0.3 13.32Interaction (F � S) * * * ns ** ** ** *

* and ** significant at p < 0.05 and 0.01; ns, not significant.

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et al. (2003) in a reaction mixture containing 50 mM sodiumphosphate buffer (pH 7.0), 0.2 mM EDTA, 0.5 mM ascorbic acid and0.25 mM H2O2. Ascorbate peroxidase (APX) activity was deter-mined bymonitoring the decline in absorbance at 290 nm for 2minas ascorbate was oxidized. Glutathione reductase (GR) activity wasdetermined by monitoring the glutathione-dependent oxidation ofNADPH at 340 nm (Kuk et al., 2003) in a reaction mixture con-taining 50 mM sodium phosphate buffer (pH 7.8), 0.2 mM NADPH,0.5 mM glutathione, 2 mM ethylene diamine tetraacetic acid andenzyme extract.

2.4. Statistical analysis

An analysis of variance was performed as in Experiment 1 andtreatment means compared similarly.

3. Results

3.1. Experiment 1

3.1.1. Yield and yield componentsMaize height was reduced (P < 0.05) by 12% under medium and

18% under low fertilizer level (Table 1) whereas it increased 20%following SAP application. Although the leaf area was also reducedby 21% under medium and low fertilization, the application of SAPsubstantially increased it by 22% and stem diameter by 18%(Table 1). The number of grains per plant also increased signifi-cantly (20%) following SAP application (Table 1) and the highestnumber was obtained under the standard fertilizer rate. Grainweight was lower under medium and low fertilizer rates but SAPincreased it on average by 14%.

The above-ground biomass (AGB) of plants treated with SAPincreased significantly by 53% with the highest value under

Table 2Leachate volume, nitrate concentration in the leachate and total amount of nitrateleaching from the lysimeter under different fertilizer and superabsorbent polymer(SAP) treatments.

Treatments Amount ofleachate (L)

Nitrate conc.(mg L�1)

Total nitrateleaching (mg)/L

Fertilizer rate (F)Standard 2.38 � 0.14 45.98 � 2.21 109.4 � 9.47Medium 2.49 � 0.16 39.75 � 1.83 98.9 � 10.89Low 2.59 � 0.16 30.66 � 2.22 79.4 � 9.69

SAP (S)Without 3.00 � 0.09 45.83 � 2.14 137.5 � 5.64With 1.96 � 0.12 31.39 � 2.51 61.5 � 4.85

LSD (0.05) 0.28 3.45 10.94Interaction (F � S) ** ** *

* and ** significant at p < 0.05 and 0.01.

standard fertilizer rate. Compared with the standard fertilizer rate,the AGB was reduced by about 14% under medium and 30% underlow fertilizer rate. Although grain yield was reduced by 20 and 38%under medium and low fertilization, the SAP increased it signifi-cantly by 86% averaged across fertilizer treatments (64.7% at low,73.7% at medium and 120.1% at high fertilizer levels). The harvestindex was also increased (P < 0.05) by about 20%.

3.2. Leaching losses

The cumulative volume of leacheate was reduced substantially(35%) with the application of SAP (Table 2) but changes in leacheatevolume due to fertilizer level were not significant. Total nitrateeNleaching was highest under the standard fertilizer rate, exceedingthat under medium fertilizer by 8% and that under low fertilizerlevel by 26% (Table 2). In contrast, SAP application significantlyreduced NO3eN leaching by 56%. Among the fertilizer regimes, theapplication of SAP reduced NO3eN leaching by 48% under standardfertilizer level, 57% under medium fertilizer level and 64% underlow fertilizer level.

3.3. Experiment 2

Under adequate irrigation, the relative water content (RWC) inthe leaves exceeded that under moderate irrigation by 8% and thatunder deficit irrigation (P < 0.05) by 18%. The application of SAPincreased the RWC by 8% under moderate irrigation and 16% underdeficit irrigation. Although plants under adequate irrigation hadmuch higher leaf water potential (j1) than those under moderateand deficit irrigation (Table 3), treatments with SAP increased thej1 by 21% under deficit irrigation.

The above- and below-ground biomass (Table 4) was increasedsignificantly by 23 and 24% following SAP application. Total biomassaccumulation under adequate irrigation exceeded that undermoderate and deficit irrigation by 19 and 48%. The application of

Table 3Relative water content (%) and leaf water potential (j1) of corn under differentsuperabsorbent polymer (SAP) and irrigation treatments.

Treatments Relative watercontent (RWC)

Leaf waterpotential (j1)

Irrigation (I)Adequate 86.52 � 0.88 �0.899 � 0.017Moderate 79.84 � 1.39 �1.259 � 0.045Deficit 70.96 � 2.08 �1.552 � 0.015

SAP (S)Without 76.35 � 2.38 �1.315 � 0.101With 81.87 � 1.43 �1.158 � 0.066LSD 0.002 �0.283

Interaction (I � S) * ns

* Significant at P < 0.05; ns, not significant.

Table 4Biomass accumulation of corn under different irrigation and superabsorbent poly-mer (SAP) treatments.

Treatments Biomass accumulation (g per plant)

Below-ground Above-ground Total

Irrigation (I)Adequate 16.76 � 0.865 50.58 � 2.198 67.35 � 2.782Moderate 14.07 � 1.082 40.75 � 3.427 54.83 � 4.116Deficit 9.45 � 1.096 25.37 � 3.977 34.82 � 4.948

SAP (S)Without SAP 12.01 � 1.315 34.83 � 4.358 46.83 � 5.581With SAP 14.85 � 0.789 42.97 � 2.811 57.83 � 3.353LSD 1.83 8. 11 10.37

Interaction (I � S) * ** **

* and ** Significant at P < 0.05 and 0.01.

A. Egrinya Eneji et al. / Journal of Cleaner Production 52 (2013) 474e480478

SAP reduced biomass accumulation by 11% under adequate irriga-tion but increased it significantly by 39% under moderate and 99%under deficit irrigation. As an indication of water deficit stress, themalondialdehyde (MDA) content in the leaves (Fig. 4) increasedsubstantially by 36% under deficit irrigation. However, SAP appli-cation significantly reduced theMDA content by about 11% averagedfor moderate and deficit irrigation. The application of SAP signifi-cantly increased the total soluble protein contents in the leaves(Fig. 4), especially under deficit irrigation. Total soluble protein washighest under adequate irrigation but decreased by 9% undermoderate irrigation and 22% under deficit irrigation.

Superoxide dismutase (SOD) activity in the leaves increased8.3% under moderate irrigation and 28.8% under deficit irrigation(Fig. 5). The activity was reduced significantly (8.9 and 21.9%) bySAP under moderate and deficit irrigation. Catalase (CAT) activity(Fig. 5) also reduced significantly (20% under moderate and 51%under deficit irrigation) following SAP application whereas theactivity increased 13% under moderate irrigation and 46% underdeficit irrigation. A Significant increase (14% under moderate

Fig. 4. Changes in malondialdehyde and soluble protein contents in corn leaves underdifferent irrigation (A ¼ adequate; M ¼ moderate; D ¼ deficit irrigation) and superabsorbent polymer (SAP) treatments. Small bars show standard errors.

Fig. 5. Superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activities incorn under various irrigation and super absorbent polymer treatments (A, M and D areas defined in Fig. 2). Small bars show standard errors.

irrigation; 34% under deficit irrigation) was observed in peroxidase(POD) activities (Fig. 5) and the activity in plants without SAPexceeded that in plants with SAP by about 12%. Ascorbate peroxi-dase (APX) level (Fig. 6) increased considerably by 13 and 35%under moderate and deficit irrigation and the level without SAPtreatments exceeded (P < 0.001) that with SAP by 14%. Glutathionereductase (GR) activity (Fig. 6) also increased under limited irri-gation and the value without SAP exceeded that with SAP by 17%.

4. Discussion

The incorporation of SAP with soil can enhance the retention oflarge quantities of water and nutrients which are released slowly asrequired by the plant to improve growth under limitedwater supply(Azzam, 1983; Huttermann et al., 1999; Yazdani et al., 2007). Thiswas confirmed in this study as the SAP reduced nitrate leaching,thereby enhancing its availability for improved maize growth andyield.

The SAP would be an effective management tool for maizecultivation in soils characterized by low water holding capacity,especially in areas where rain or irrigationwater and fertilizer often

Fig. 6. Ascorbate Peroxidase (APX) and Glutathione Reductase (GR) activities in cornunder various irrigation and super absorbent polymer treatments (A, M and D are asdefined in Fig. 2). Small bars show standard errors.

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leach below the root zone, leading to poor water and fertilizer useefficiency by crops (Johnson, 1984; Mikkelsen, 1994). Whenaqueous nutrient-containing solutions are used to hydrate a poly-mer, a considerable amount of nutrient enters into the polymerstructure during expansion (Martin et al., 1993; Woodhouse andJohnson, 1991). Mikkelsen et al. (1993) showed that addition ofpolymer to fertilizer solutions reduced N leaching from soil col-umns as much as 45% during the first four weeks in heavily leachedconditions compared with N fertilizer alone. At the same time,Fescue (Festuca arundinacea L.) growth was also increased as muchas 40% and tissue N accumulation increased up to 50% whenfertilized with polymer compared with fertilizer alone. Magalhaeset al. (1987) showed a remarkable reduction in NH4, P and Kleaching due to the presence of the polymer. Our result also showeda remarkable consistency with the above reports based on thereduction in NO3 leaching in presence of SAP (Table 2).

Although Grain yield was reduced by 19.7% under medium and37.7% under low fertilizer level, across fertilizer levels, the appli-cation of SAP increased it significantly by 86%. Similarly, othergrowth parameters (Table 1) and grain quality also increased.Considering the trends in growth reduction (qualitative andquantitative) due to fertilizer reduction and the positive influenceof SAP on these parameters, it was clear that the application of SAPat 30 kg ha�1 plus half the conventional fertilizer rate could achievethe same yield as conventional fertilizer rate. This SAP rate maxi-mized nitrate retention in the soil and minimized leaching losses.

The SAP also had a marked positive effect on corn growth espe-cially under limited water supply by substantially increasing therelative water content and leaf water potential, especially underdeficit irrigation (Table 1). Previous research at field and laboratorylevels also showed similar results (Azzam, 1983; Huttermann et al.,1999; Yazdani et al., 2007). The relative water content is a reliablemeasure of plant water status, considering the physiologicalconsequence of cellular water deficit while water potential as an

estimate of plant water status is useful in dealing with watertransport in the soil-plant-atmosphere continuum (Kramer, 1988).

Deficit irrigation induced significant increases in SOD, CAT, POD,APX and GR activities (Figs. 4 and 5) in the leaves due to increasedoxidative stress in the plant as expressed by lipid peroxidation.Because maize is considered moderately drought tolerant (Riccardiet al., 1998; Azooz et al., 2009), it might have inadequate ROSscavenging system or other tolerance mechanisms to cope withstress. Our data showed that, the super absorbent polymerdecreased the activity and expression of these enzymes as anindication of stress alleviation, since the SAP conserves water initself, thereby increasing the soil’s capacity for water storage andpreservation and preventing water deficiency for enhanced growth(Tohidi-Moghadam et al., 2009). Whereas, the application of SAPreduced biomass accumulation under adequate irrigation, it almostdoubled the biomass under deficit irrigation. The effectiveness ofSAP would be more visible under water-stress conditions.

5. Conclusion

The superabsorbent polymer conserved different amounts ofwater and fertilizer and improved plant growth and yield underwater stress. Combining SAP with only half the conventionalfertilizer rate was as adequate for corn growth and productivity asthe standard fertilizer rate with the additional advantage ofreducing leaching by as much as 64%. Also, the use of SAP canenhance maize survivability at the physiological level underdrought stress and could thus be an effective soil managementpractice for maize production under conditions of drought.

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