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Ecological Engineering 62 (2014) 27– 32

Contents lists available at ScienceDirect

Ecological Engineering

journa l h om epage: www.elsev ier .com/ locate /eco leng

nfluence of super absorbent polymer on soil water retention, seedermination and plant survivals for rocky slopes eco-engineering

ixia Yanga,b, Yang Yangb, Zhang Chena, Chunxiao Guoc, Shaocai Lia,∗

College of Life Science, Sichuan University, Chengdu 610064, PR ChinaAdministrative Committee of Qingdao Dongjiakou Economic Zone, Qingdao 266409, PR ChinaCollege of Life Science, Qufu Normal University, Qufu 273165, PR China

r t i c l e i n f o

rticle history:eceived 20 July 2013eceived in revised form 2 October 2013ccepted 15 October 2013vailable online 13 November 2013

eywords:

a b s t r a c t

To improve the utilization of water resources on rocky slopes eco-engineering, super absorbent polymer(SAP) with the function of water retention was applied. Super absorbent polymer in three levels, 0.15%,0.3% and 0.45% were mixed with sandy loam soil. This study was aimed to evaluate the saturated watercontent, evaporation rate and water holding capability of SAP treated soils, determine seed germinationrate and plant survivals in soil with SAP by absorbing and spraying experiments. The addition of SAP tothe sandy loam soil resulted in a significant increase of the soil water retention compared to the controls.

uper absorbent polymerater retention

ocky slopes eco-engineering

Also, the seed germination was significantly higher in SAP amended soil than in the soil without SAP,survival times of grass and woody were prolonged under water stress. 0.30% SAP treatment was theoptimum selection for sandy loam soil improvement on steep rocky slopes. These studies indicated thatSAP with good water retention properties, was very effective in enhancing water uptake and utilizationof water for plants growth, and could be expected to have wide potential applications in rocky slopeseco-engineering.

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. Introduction

Extensive highway constructions have resulted in large num-ers of steep rocky slopes, causing soil loss, and an unbalancedco-environment (Zhou and Zhang, 2003; Koca and Kıncal, 2004;ang et al., 2011). To restore the ecological balance of the bare rockylopes, eco-engineering is an important way to create the appropri-te condition necessary for plant growth, enhance slopes stabilityy mechanical reinforcement of plant roots, and improve ecologi-al environment through hydrologic effect of aboveground biomassZhou and Zhang, 2003; Yang et al., 2011; Chen et al., 2004). In addi-ion to the steep slopes recovery, the presence of water in soil isssential for plant survival. Thus, it is important to determine theppropriate materials with which to improve the water-holdingapacity of soil on rocky slopes. Taking into account the watermbibing characteristics of super absorbent polymer (SAP) materi-ls, its application in rocky slope eco-engineering may be alleviatehese problems (Zohuriaan-Mehr and Kabiri, 2008).

Super absorbent polymers are compounds that absorb waternd swell into many times their original size and weight. Superbsorbent polymers are used in soil to create a water reserve, near

∗ Corresponding author. Tel.: +86 532 84181864; fax: +86 532 84181864.E-mail address: lxy0543@gmail.com (S. Li).

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925-8574/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.ecoleng.2013.10.019

© 2013 Elsevier B.V. All rights reserved.

he rhizosphere zone (roots) and benefit agriculture (Zohuriaan-ehr and Kabiri, 2008; Han et al., 2010). Current studies on SAPainly focused on the development of its new material and new

roduct and its own chemical properties as well as its field applica-ion (Yang et al., 2003; Han et al., 2005, 2010). Various applicationsf SAPs and active fields of applied research works on SAPs haveeen made. It was first applied in agricultural production of cornnd soybean as well as seedling transplanting. Fanta et al. (1971)ound that SAP contributed to water saving and yield enhancement.ater, SAP is also used in many areas such as pharmaceuticals,ood packaging, paper production, the agricultural and horticul-ural industry, oil drilling, etc. (Wang et al., 1998, 2000a,b; Li et al.,004; Han et al., 2010).

In the agriculture and horticultural industry, the application ofAP is in the form of seed additives, seed coatings, root dips, ando on (Zohuriaan-Mehr and Kabiri, 2008). Since SAP can ease theurden of water shortage, proper use is helpful in arid and semi-rid areas (Bakass et al., 2002; Zohuriaan-Mehr and Kabiri, 2008;an et al., 2010). It has positive effect on water retention on various

ypes of soils, can improve the physical properties of soil in viewf increasing their water-holding capacity and nutrient retention

f soil, delay the time to reach permanent wilting point, prolonglant survival under water stress (Hüttermann et al., 1999; Oscroftt al., 2000; Viero et al., 2002; Abedi-Koupai and Asadkazemi, 2006;rikiriza et al., 2009).

28 L. Yang et al. / Ecological Engineering 62 (2014) 27– 32

Table 1Soil physical and chemical properties.

Texture Particle size fraction (%) CEC (cmol(c) kg−1) OM (g kg−1) pH

Clay Silt Sand

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Sandy loam 11.31 18.53 70.16

EC, cation exchange capacity; OM, organic matter.

In most researches, SAP was applied directly onto the soil sur-ace. The use of SAP in disturbed soils on rocky slopes, however,

ay have different results. In this study, we aimed to investigatehe influence of SAP on water retention, seed germination and planturvivals via hydro-seeding technology on a 60◦ rocky slope. Welso plan to determine the optimal dose for sandy loam soil tomprove water retention and life span of plants under water stressonditions. Understanding the influence of SAP on soils will beelpful to promote SAP application to rocky slopes eco-engineeringhere the availability of water is insufficient.

. Materials and methods

.1. Materials

Soil used in the experiments was sandy loam, which was col-ected from the top 15 cm of the field in Chengdu, China (103◦53′ E,0◦59′ N). The area is a humid subtropical climate and basin topog-aphy, receives about 932.5 mm average rainfall, with a 15.6 ◦Cean annual temperature, a maximum annual temperature of

7.7 ◦C and a minimum of −5.1 ◦C during the last 30 years. Uponeturn to the lab, the soil was air-dried, and sieved to pass a 4.0 mmcreen, to remove the identifiable root material during the process.oil was stored at 25 ◦C until being used. Physical and chemicalroperties of the selected soil are shown in Table 1.

Super absorbent polymer sample was provided by SIDA Co.,eijing, China. It was white powders with a particle diameter of0–250 �m, with the following concentrations added to the soil:

(the control), 0.15%, 0.3%, and 0.45%. The properties of SAP arehown in Table 2.

Seeds used in this study were Medicago sativa L., Festucarundinacea Schreb., Melilotus suaveolens Ledeb., Leucaena glauca,ndigofera pseudotinctoria Matsum., Indigofera amblyantha Craib.,morpha fruticosa Linn., Sophora viciifolia Hance, Lespedeza FormosaVog.) Koehne, Robinia pseudoacacia Linn.

.2. Experimental design and measurements

In this study, three levels of SAP content were mixed with sandyoam soil, three replicates. Soil moisture characteristics and therowth of applicable plants were conducted in the absorbing andpraying experiments.

.2.1. Absorbing experimentThe absorbing experiment was carried out in a glass-house (with

othing surrounding the glass top) in April, 2010. The samples were

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able 2he properties of super absorbent polymer.

Water content (%) Grain size (�m) Water uptake capacity

Distilled water

10.05 50–250 292

15.2 15.3 6.5

repared as follows: 1020.0 g mixture including soil and SAP waslaced in a 20-cm diam. by 4-cm ht. PVC cylinder. The cylinder wasVC slab with holes and a #1 Whatman filter paper on the bottom.ylinders were set into trays for 48 h, and then transferred to thelass-house. The weight of the cylinders was recorded daily untilo noticeable weight loss was observed. Saturated water content,vaporation rate and water holding capacity were calculated by theollowing equation:

= (W1 − W2 − 1020.0) ∗ 1001020.0

Rn = (Wn − Wn − 1) ∗ 100W1 − W2 − 1020.0

HC = (W1 − W2 − 1020.0) ∗(

1 −∑ ERn

100

)

here W% is the saturated water content, W1 the total weight ofaturated soil and cylinder (g), W2 the weight of cylinder (g), ERn

he evaporation rate (%), Wn and Wn − 1 the total weight of soil andylinder on the n and n − 1 day (g), WHC the water holding capacityg),

∑ERn the sum of evaporation on the n day (%).

.2.2. Spraying experimentA modified hydro-seeding technology (Zhang et al., 2013; Li

t al., 2005, 2006) was conducted in the bioengineering sta-ilization laboratory of Sichuan University, China. The process

llustrated as follows: Soil, pretreated seeds and SAP were mixedsing a concrete mixer (JZC300, Henan Kowloon Machinery Co.,td., Zhengzhou, China). The mixture was transferred into aompressed-air spraying machine (12 m3, Ingersoll-Rand, Piscat-way, NJ) by a rotor concrete conveyer (5 m3 h−1, V-6/7, Hunanhangde Universal Compressor Co., Ltd., Changde, China). Undererodynamic force, the mixture was blended with water at the out-et of the spraying machine and sprayed onto soil trays through aonveying pipeline (20 m long, 75 mm in diameter) (Yang et al.,011; Chen et al., 2004). The spraying pressure was 0.12 MPa andhe water discharge volume was 10 L min−1.

The soil was covered with straw on the surface after spraying,nd was put in natural condition after 24 h. The soil tray with 1.4 mong, 0.7 m wide and 0.1 m deep was set to a gradient of 60◦. A

-shaped runoff collector was connected by flexible tubing, which

ransferred the runoff into a sampling barrel. (Yang et al., 2011)Fig. 1). Runoff was recorded by electronic balance after rainfall,nd soil water absorption was determined by subtracting the runoff

(g/g) Grain composition (%)

Tap water NaCl 0.9%

220 45 0.5–1 mm: 0.05%;0.25–0.5 mm: 0.06%0.15–0.25 mm: 29.40%;<0.25 mm: 70.1%

L. Yang et al. / Ecological Engineering 62 (2014) 27– 32 29

Fig. 1. Schematic diagram for the experimental set up. (a) Rainfall; (b) soil tray;(b

fts

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Fig. 2. Effect of SAP application on saturated moist content of soil. 0.15%, 0.30%, and0.45% indicate SAP content in soil. CK, soil with no SAP. Values represent the mean ofthree replicates. Error bars represent standard deviation. Bars with different lettersi

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c) runoff collector; (d) energy dissipating plate; (e) sampling barrel; (f) electronicalance.

rom the rainfall, calculated by the following equation. Germina-ion rate was determined by the ratio of highest germination andeeding amount.

= P ∗ S ∗ cos ̨ − R

S

here I is the water absorption (mm), P is the precipitation (mm), is the slope area (m2), ̨ is the gradient (◦), R is the runoff (kg).

After 50 days, the soil trays were transferred into the glass-ouse with no watering, survival time of plants was calculated byubtracting the date of stop watering from the date of death of eachndividual plant. Death of plants was monitored by observing on aaily basis the color change of leaves and branches from green torown and gray. When all the leaves and stems turned brown andtarted shedding off, and branches becoming brittle, the plant waseclared dead (Agaba et al., 2010).

.3. Statistical analysis

A one-way analysis of variance was carried out to determinehe main effects of SAP content on water absorption rate, evapo-ation rate, seed germination rate and survival times. Significant

du(

ndicate significant differences at p < 0.05.

ifference (LSD) test at ̨ = 0.05 level. All statistical analysis waserformed using SPSS 16.0 for Windows (SPSS Inc., Chicago, IL).

. Results

.1. Absorbing experiment

.1.1. Saturated water absorptionAll SAP treatments significantly increased saturated water con-

ent with increasing of the SAP content compared with the controlsFig. 2). The maximum saturated water content was achieved whenhe SAP content was 0.45%, with a 42.69% increase compared withhe controls. The 0.15% SAP treatment worked worst, but still hadn increase of about 11.20%.

.1.2. Evaporation rateDuring the first 5 days, all SAP treatments reduced the evap-

ration rate compared with the controls. The efficiency of SAPreatments increased with increasing SAP content. The evapora-ion rate of soil without SAP had reached 26.84% on the 10th day,hereas that of soil with 0.45% SAP was 4.75%. After 5 days, no

eduction in evaporation rate was observed in the SAP treated soils.n fact, opposite trend was found, soil with high SAP content lost

ore water than the controls, the evaporation rate of soil withoutAP was 3.25% on the 6th day, whereas that of soil with 0.45% SAPad reached 27.95% (Fig. 3).

.1.3. Water holding capacityAll SAP treatments significantly increased soil water holding

apacity with increasing SAP content compared with the controls.n the 3rd day, the 0.45% SAP treatment performed best, increasingy 203.47% compared with the controls, even the 0.15% SAP treat-ent still increased by 108.91%. Soil without SAP was completely

ry at the end of 6 days, while soil with 0.15% SAP was not dryntil 10th day, soil with 0.3% and 0.45% SAP was dry after 11 daysFig. 3).

30 L. Yang et al. / Ecological Engineering 62 (2014) 27– 32

Fig. 3. Effects of SAP application on evaporation rate and water holding capacity.0.15%, 0.30%, and 0.45% indicate SAP content in soil. CK, soil with no SAP. Evapo-rcd

3

3

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Fig. 4. Effect of SAP application on water absorption during the rainfall processes.0.15%, 0.30%, and 0.45% indicate SAP content in soil. CK, soil with no SAP. A, B, C, D, E,F, G, H and indicated rainfall intensity of 0.73, 0.92, 1.40, 1.85, 2.06, 3.23, 3.93, 4.77and 5.43 mm h−1, respectively. Values represent the mean of three replicates. Errorbars represent standard deviation. Bars with different letters indicate significantdifferences at p < 0.05.

Fig. 5. Effect of SAP application on germination rate of seeds. 0.15%, 0.30%, and0.45% indicate SAP content in soil. CK, soil with no SAP. Values represent the mean ofthree replicates. Error bars represent standard deviation. Bars with different lettersindicate significant differences at p < 0.05.

Table 4Survival time of the grass and woody after the last watering.

Treatment Survival time (days)

ation rate was expressed by bars, and water holding capacity was expressed byurves. Values represent the mean of three replicates. Error bars represent standardeviation. Bars with different letters indicate significant differences at p < 0.05.

.2. Spraying experiment

.2.1. Water absorptionSuper absorbent polymer content and rainfall intensity were

oth significant factors influencing soil water holding capacity,nd there was significant interaction between the two factorsTable 3). All SAP treatments increased water absorption rate by9.3% to 139.4% compared with the controls. Water absorptionates increased with increasing SAP content under the rainfallntensity of 3.93, 4.77 and 5.43 mm h−1 (Fig. 4).

.2.2. GerminationBoth grass and the woody germination rates were increased

nder SAP treatments compared with the controls. The plant ger-ination rates increased with increasing SAP content. Amending

andy loam soil with 0.45% SAP significantly increased more thanwo fold in grass germination rate compared with the controls, andbout 3.5-fold in the woody. While amendment at 0.15% SAP had aignificant twofold in grass and woody compared with the controlsFig. 5).

.2.3. Survival timeThe survival time of grass and woody in soil with SAP was

xtended. For 0.3% and 0.45% SAP treatments, the survival time ofrass and woody were both doubled compared with the controls,urviving for 18 and 21 days, respectively. Woody in soil with 0.45%AP had the maximum life span (21 days) compared to the control11 days). However, there was no significant difference between.3% and 0.45% SAP treatments. Even more, the survival time of

rass plant with 0.3% SAP treatment was longer than that of 0.45%AP treatment (Table 4).

able 3nalysis of variance for water absorption under variable rainfall intensity.

Source of variation df Mean square P

SAP content (S) 3 1742.38 <0.001Rainfall intensity (R) 8 566.5 <0.001S × R 24 17.24 <0.001Error 72 0.803

Grass Woody

CK 9 ± 1a 11 ± 1a0.15% 13 ± 1b 14 ± 0b0.30% 18 ± 2c 19 ± 1c

0

4

o

0.45% 17 ± 1c 21 ± 1c

.15%, 0.30%, and 0.45% indicate SAP content in soil. CK, soil with no SAP.

. Discussion

The results indicate that the addition of SAP to soil couldbviously increase the water retention of the soil. This could be

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L. Yang et al. / Ecologica

ttributed to the three-dimensional cross-linked structure of SAP.he high cross-linked SAP can absorb and hold up to 400 times theireight of water (Orikiriza et al., 2009; Hüttermann et al., 1999). Itas strong adsorption and complexing capacities for its hydrophilic

unctional groups, such as hydroxyl, carboxyl, amide, and sulfonicroups. Water moisture enters into the internal network easily,nd forms a water-blocking layer between soil particles when theolecular chain swelled under the three-dimensional cross-linked

tructure, which could inhibit moisture from moving either fromoil surface to the atmosphere or to rock layer of slopes, but make itoving horizontally, or to the place that had little SAP (Flory, 1971;üttermann et al., 2009).

During the first 5 days in the absorbing experiment, the evapo-ation rate of soil with SAP reduced. It might be explained on theasis of hydraulic lift and hydraulic conductivity of soil. Hydraulic

ift is the nocturnal resupply of water in the upper soil layers whichave been depleted during daytime (Richards and Caldwell, 1987).he hydraulic conductivity of soil is influenced by the particle sizeistribution of soil (Arya et al., 1999) and is a function of soil textureHultine et al., 2006). Amendment with polymer could decreasehe hydraulic conductivity of soils (Bhardwaj et al., 2007; Agabat al., 2010). Furthermore, the soil with SAP treatment can absorbore water than soil without SAP and allows the absorbed water

o be released slowly when the soil moisture decreases (Al-Darby,996; El-Rehim et al., 2004; Chen et al., 2004; Ni et al., 2010). Sim-

lar observations have been reported by Bakass et al. (2002) whouggested that the presence of the polymer in the soil made it pos-ible to preserve water longer than a soil without the polymer did,void the evaporation phenomenon which was observed just at theeginning of the drying reaction of the soil.

Furthermore, soils amended with higher concentrations of SAPeleased more water than the controls during the stress period. Ithould be attributed to the chemical hydrophilic groups and net-ork structure in SAP hydrogel molecule. The water moleculesere charged by weak connections and could involve a good

xchange of water between the polymer and the soil (Bakass et al.,002). Bakass et al. (2002) reported that polymer could absorb aery significant quantity of water, but dried first before the soil dur-ng drying period. The results also concord with that of Hüttermannt al. (1999), who observed that soil with highest concentration ofydrogels lost more water during water stress period.

In addition, there was a dramatic advantage of SAP treatmentsn seed germination and plant survivals compared with otherreatments. The results indicate that an amendment of SAP wouldreatly enhance the drought tolerance of the seedlings planted inandy loam soil. This could be attributed to water storage and nutri-nt retention in the soil matrix. By amending the soil with SAP, andditional system was incorporated into the soil which had bothigh water retention and a high water potential. It was possible toave water by reducing the water losses through infiltration andvaporation, increasing the duration of the presence of water inhe soil, which could improve the life span and quality of plantsBakass et al., 2002; Abedi-Koupai and Asadkazemi, 2006; Agabat al., 2010). Furthermore, soil with SAP could absorb more waterhan soil without SAP and allow the absorbed water to be releasedlowly when the soil moisture decreased, and fertilizer nutrientsould also be released slowly with water decreases, nutrient reten-ion in hydrogel amended substrate could be increased (Ni et al.,010; Agaba et al., 2010). Thus, the utilization of water and fertil-

zer was improved efficiently, seed germination was increased, andurvival times of plant were prolonged under water stress.

However, no significant difference was observed between 0.30%nd 0.45% SAP treatments on the survival time of plants, moreover,he survival time of grass plant in soil with 0.3% SAP was longerhan that of 0.45% SAP treatment. It might be explained on the basis

H

neering 62 (2014) 27– 32 31

f water utilization efficiency of plant. Although there was muchore water in the soil with 0.45% SAP than soil with 0.3% SAP during

he initial stage, a significant part of water stored by hydrogel waspparently not available for the plants (Hüttermann et al., 1999).s a result, 0.45% SAP treatment did not appear to have significantdvantage in extending plants life span compared with the 0.30%AP treatment during the water stress period.

. Conclusion

In conclusion, the amendment of soils with SAP considerablynhanced water uptake and utilization of water for plants growth,he 0.45% SAP treatment worked best. The saturated moist contentncreased by 42.69% and 139.38% compared with the controls inat soil and the 60◦ slope soil, respectively. The evaporation rateecreased by 88.85% compared with the controls. Germination rate

ncreased more than 2 times in grass, and about 3.5 times in woodyompared with the controls. However, no significant difference wasbserved between 0.45% and 0.30% SAP treatments in extendinglants life span. All in all, with respect to the water retention effi-iency of soil with SAP amendment and the project cost, 0.30% SAPreatment was the optimum selection for sandy loam soil improve-

ent on steep rocky slopes. In addition, straw was covered on theurface of the soil in our study. So, soil erosion was not the focus ofur study. The effect of SAP amendment on soil erosion would betudied in the next periods.

cknowledgments

Our research was supported by the National Key Technologiesupporting Program of China during the 11th Five-Year Plan PeriodNo. 2007BAQ00040). The authors thank Mr. Tao-Yang for his tech-ical assistance, and Prof. Lei-He for valuable discussions of thisaper.

eferences

bedi-Koupai, J., Asadkazemi, J., 2006. Effects of a hydrophilic polymer on thefield performance of an ornamental plant (Cupressus arizonica) under reducedirrigation regimes. Iran. Polym. J. 15, 715–725.

gaba, H., Baguma Orikiriza, L.J., Esegu, O., Francis, J., Obua, J., Kabasa, J.D., Hüt-termann, A., 2010. Effects of hydrogel amendment to different soils on plantavailable water and survival of trees under drought conditions. Clean Soil AirWater 38, 328–335.

l-Darby, A., 1996. The hydraulic properties of a sandy soil treated with gel-formingsoil conditioner. Soil Technol. 9, 15–28.

rya, L.M., Leij, F.J., Shouse, P.J., Van Genuchten, M.T., 1999. Relationship betweenthe hydraulic conductivity function and the particle-size distribution. Soil Sci.Soc. Am. J. 63, 1063–1070.

akass, M., Mokhlisse, A., Lallemant, M., 2002. Absorption and desorption of liquidwater by a superabsorbent polymer: effect of polymer in the drying of the soiland the quality of certain plants. J. Appl. Polym. Sci. 83, 234–243.

hardwaj, A.K., Shainberg, I., Goldstein, D., Warrington, D.N., Levy, G., 2007. Waterretention and hydraulic conductivity of cross-linked polyacrylamides in sandysoils. Soil Sci. Soc. Am. J. 71, 406–412.

hen, P., Zhang, W.A., Luo, W., Fang, Y.E., 2004. Synthesis of superabsorbent poly-mers by irradiation and their applications in agriculture. J. Appl. Polym. Sci. 93,1748–1755.

l-Rehim, H.A., Hegazy, E.S.A., El-Mohdy, H.L., 2004. Radiation synthesis of hydrogelsto enhance sandy soils water retention and increase plant performance. J. Appl.Polym. Sci. 93, 1360–1371.

anta, G.F., Burr, R.C., Doane, W.M., 1971. Influence of starch-granule swelling ongraft-copolymer composition. A comparison of monomers. J. Appl. Polym. Sci.15, 2651–2660.

lory, P.J., 1971. Principles of Polymer Chemistry, 8th ed. Cornell University Press,Ithaca, NY.

an, Y.G., Yang, Y.P., Xu, L., 2005. Experimental studies on increase of yield and soil

moisture of fruit tree by using super absorbent polymers. Sci. Agric. Sin. 38,2486–2491.

an, Y.G., Yang, P.L., Luo, Y.P., Ren, S.M., Zhang, L.X., Xu, L., 2010. Porosity changemodel for watered super absorbent polymer-treated soil. Environ. Earth Sci. 61,1197–1205.

3 l Engi

H

H

H

K

L

L

L

N

O

O

R

V

W

W

W

Y

Y

Z

2 L. Yang et al. / Ecologica

ultine, K., Koepke, D.F., Pockman, W.T., Fravolini, A., Sperry, J.S., Williams, D.G.,2006. Influence of soil texture on hydraulic properties and water relations of adominant warm-desert phreatophyte. Tree Physiol. 26, 313–323.

üttermann, A., Zommorodi, M., Reise, K., 1999. Addition of hydrogels to soil forprolonging the survival of Pinus halepensis seedlings subjected to drought. SoilTill. Res. 50, 295–304.

üttermann, A., Orikiriza, L.J.B., Agaba, H., 2009. Application of superabsorbent poly-mers for improving the ecological chemistry of degraded or polluted lands. CleanSoil Air Water 37, 517–526.

oca, M.Y., Kıncal, C., 2004. Abandoned stone quarries in and around the Izmir citycentre and their geo-environmental impacts—Turkey. Eng. Geol. 75, 49–67.

i, D.J., Yang, P.L., Han, Y.G., 2004. Application effects of super absorbent polymers ongrape cultivation. In: Huang, G.H., Luis, S.P. (Eds.), Land and Water ManagementDecision Tools and Practices. Agricultural Science and Technology PublishingHouse, China, Beijing, pp. 798–803.

i, S.C., Sun, H.L., Yang, Z.R., He, L., Cui, B.S., 2005. Effect of spraying techniques andsoil texture on ecoengineering for rock slope protection. Chn. J. Rock Mech. Eng.24, 5374–5381.

i, S.C., Sun, H.L., Yang, Z.R., He, L., Cui, B.S., 2006. Effect of straw fiber, polyacrylamideand super absorbent polymer eco-engineering on rock slope protection. Chn. J.Rock Mech. Eng. 25, 257–267.

i, B., Liu, M.Z., Lü, S.Y., Xie, L., Zhang, X., Wang, Y.F., 2010. Novel slow-release mul-tielement compound fertilizer with hydroscopicity and moisture preservation.Ind. Eng. Chem. Res. 49, 4546–4552.

rikiriza, L.J.B., Agaba, H., Tweheyo, M., Eilu, G., Kabasa, J.D., Hüttermann, A., 2009.

Amending soils with hydrogels increases the biomass of nine tree species undernon-water stress conditions. Clean Soil Air Water 37, 615–620.

scroft, D.G., Little, K.M., Vireo, P.W.M., 2000. The Effect of a Soil-Amended Hydrogelon the Establishment of Pinus elliottii × caribaea Rooted Cuttings on the ZululandCoastal Sands (ICFR Bulletin Series), vol. 19. ICFR, pp. 8.

Z

Z

neering 62 (2014) 27– 32

ichards, J.H., Caldwell, M.M., 1987. Hydraulic lift: substantial nocturnal watertransport between soil layers by Artemisia tridentata roots. Oecologia 73,486–489.

iero, P.W.M., Chiswell, K.E.A., Theron, J.M., 2002. The effect of a soil amendedhydrogel on the establishment of a Eucalyptus grandis clone on a sandyclay loam soil in Zululand during winter. Southern Afr. Forest. J. 193,65–75.

ang, G.J., Li, M., Chen, X.F., 1998. Preparation and water-absorbent properties of awater-swellable rubber. J. Appl. Polym. Sci. 68, 1219–1224.

ang, B.R., He, K.N., Shi, C.Q., 2000a. The application of super absorbentpolymers in the forestation and virescence. J. Soil Water Conserv. 4,22–24.

ang, W.Z., Rong, J.C., She, W.N., 2000b. The characteristics and application of thefilling ointment of water-absorbent expansive water blocking cable. J. Electr.Insul. Mater. 3, 22–24.

ang, L.X., Li, S.C., Sun, H.L., Ye, F.F., Liu, W., Luo, S., 2011. Polyacrylamide molecularformulation effects on erosion control of disturbed soil on steep rocky slopes.Can. J. Soil Sci. 91, 917–924.

ang, P.L., Wang, C.Z., Ren, S.M., Li, Y.K., Xu, T.W., 2003. Experimental studies of affec-tions on the absorbable and holding characteristics of water-retaining agent indifferent solution environments and the approaches to increasing its field effi-ciency. J. Exp. Bot., 31 (Oxford Univiversity Press, Great Clarendon ST, OxfordOX2 6DP, England).

hang, C., Yang, L.X., Jiang, Z.Q., Li, C.J., Hu, X., Pang, L., Li, S.C., Sun, H.L., 2013. Runoff-driven nitrogen and phosphorus dynamics of substrate material for rocky slope

eco-engineering. Ecol. Eng. 51, 123–132.

hou, D.P., Zhang, J.Y., 2003. Vegetation Protection Techniques of Slopes. ChinaCommunication Press, Beijing, China.

ohuriaan-Mehr, M.J., Kabiri, K., 2008. Superabsorbent polymer materials: a review.Iran. Polym. J. 17, 451–477.