Aggregation and fractal dimension of aggregates …...European Journal of Soil Science, September...

$: Aggregation and fractal dimension of aggregates …...European Journal of Soil Science, September 2017, 68, 783–791 doi: 10.1111/ejss.12458 Aggregation and fractal dimension of aggregates$
European Journal of Soil Science, September 2017, 68, 783–791 doi: 10.1111/ejss.12458

Aggregation and fractal dimension of aggregates formed insand dunes stabilized by PistachioPAM and PistachioPVAcmulches

N . S a i e d i a, A . A . B e s a l a t p o u r a , H . S h i r a n i a, P . A b b a s z a d e h D e h a j i a,I . E s f a n d i a r p o u r a & M . F a r a m a r z i b

aDepartment of Soil Science, College of Agriculture, Vali-e-Asr University of Rafsanjan, University street, PO Box 518 Rafsanjan, Iran, andbDepartment of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada

Summary

Wind erosion is a serious environmental problem that has received increased attention by attracting the interest ofacademics, policy makers and the public. In this study, the effects of combined mulches (denoted as PistachioPAMand PistachioPVAc, used for stabilizing the sand dunes in the Davaran plain in southeastern Iran) on aggregateformation and stability indices were investigated by the theory of fractal geometry. In addition, the temporalchanges in soil organic carbon (SOC) content and microbial respiration rate (MRR) in the soils treated with themulches were compared with the control samples during a 5-month experiment. The results showed significant(P< 0.01) increases in the SOC content and MRR following the application (1.5 l m−2) of PistachioPVAc andPistachioPAM mulches. The rate of release of CO2 was measured in the soils treated with the mulches studied.The largest rate of CO2 release from the three samples taken in weeks 2, 5 and 19 from the beginning of theexperiment was about 23.0 μg-CO2 day−1 g−1 soil. The smallest and largest mean weight diameters (MWD) ofthe aggregates formed were observed in the control (0.06 mm) and the PistachioPVAc (1.38 mm) treatments,respectively. The use of mulches had significant (P< 0.01) effects on the fractal dimension of aggregates. Themore stable and coarser aggregates formed in the presence of PistachioPVAc had the smallest fractal dimension.The largest negative correlation between the properties investigated and the fractal dimension was for SOC andMWD. Therefore, it appears that the theory of fractal dimensions is useful for explaining the temporal variationof aggregate stability in soil stabilized by combined mulches.

Highlights

• Effects of combined mulches on aggregate formation were investigated with fractal geometry theory (FGT).• The more stable and coarser aggregates formed in the presence of PistachioPVA mulch had the smallest fractal

dimension.• Mulches increased soil organic carbon and microbial respiration significantly (P< 0.01).• The FGT might be useful for explaining the temporal variation in aggregate stability of stabilized sand dunes.

Introduction

Wind erosion, as a natural phenomenon, can be controlled throughknowledge, awareness, planning and proper management, as withother natural phenomena, to minimize its detrimental effects (Lopezet al., 2007; Zhang et al., 2017). Because of the large costs of wind

Correspondence: A. A. Besalatpour. E-mail: [email protected];[email protected] 1 August 2016; revised version accepted 25 May 2017

erosion control and difficult working conditions, determining theprinciples and technical practices to stabilize the soil in affectedregions would be effective in reducing the costs (Zezin et al.,2015). There are various methods that may be used to controlerosive agents (such as wind and water). The three main waysto stabilize sand dunes are chemical, biological and mechanicalmethods (Goudie & Middleton, 2006). The most efficient methodfor controlling wind erosion is to cover the ground surface withvegetation; the greater the vegetation cover, the more effective itwill be (He et al., 2008; Kim et al., 2017). In the case of potential

© 2017 British Society of Soil Science 783

http://orcid.org/0000-0003-4443-1454

784 N. Saiedi et al.

failure to establish plants, mechanical and chemical methods suchas the spraying of mulches could be used (Movahedan et al., 2012).

Over the past half-century, various materials have been evaluatedto find suitable stabilizers for controlling wind erosion (Hagen,2010). In Iran, for instance, oil mulches have been widely used fortemporary stabilization of sand dunes. About 20 million hectares ofthe country is affected by wind erosion, which has resulted in theformation of dry lands with about 5 million hectares of active andsemi-active sand dunes. The usual method to prevent wind erosionin such areas is the use of oil mulches. The latter are useful for thestabilization of sand dunes, but they might reduce water infiltrationand lead to diurnal and seasonal fluctuations in soil temperature(Amiraslani & Dragovich, 2011). In the summer months, thereis a small overall temperature difference between mulched andbare soils. However, mulched soil is warmer in spring, winter andautumn, but it warms more slowly in the spring. Furthermore,oil mulches contain heavy metals such as lead. Therefore, theiruse can cause serious environmental damage with the dispersionof these pollutants by the wind (Jahanjo, 2000). Because of theadverse effects of oil mulches and the high costs of their application,comprehensive research on the production of new eco-friendlymulches is vital.

PistachioPAM and PistachioPVAc are novel combined mulches,which are made of an optimum ratio of pistachio residues, andpolyacrylamide (PAM) and polyvinyl acetate (PVAc), respectively,and water after extensive trials. The pistachio residues are availablefrom the harvest of about 400 000 t of pistachio nuts near the cityof Rafsanjan, southeastern Iran (Mohammadi Moghaddam, 2008).The principal mechanisms to control dust and wind erosion bythese mulches are the formation of soil aggregates, improvementof structural stability and production of an erosion-resistant surfacelayer to prevent soil particle ablation and the generation of dust.Some of the ways of preventing the removal and movement of soilparticles by wind erosion include the bonding of soil particles andimprovement in soil aggregate stability with organic-based mulchessimilar to ours (Luna et al., 2016).

A practical measure for evaluating the effectiveness of mulchesin the improvement in soil aggregate stability is to calculate thefractal dimension of aggregates formed (Gregory et al., 2012).For example, Ahmadi et al. (2011) found that the breakdown ofaggregates and weighted fractal dimensions obtained from the wetsieving method had a significant and positive correlation witherodibility, splash erosion and rill erosion. They concluded that soilerosion could be predicted by calculating the fractal dimension ofaggregates. Soil fractal dimension can also be used as an indicator ofthe degree of disturbance of the soil because it shows the mechanicaldisruption of the soil pores. Su et al. (2004) suggested that the fractaldimension of soil aggregates is associated with the desertificationof cultivated lands, and concluded that the large sand contentsand small fractal dimension of soil aggregates will increase thepropensity for soil desertification.

Given that the soil in arid and semi arid areas has small amountsof organic matter and weak structural stability, it is more susceptibleto erosion, degradation and desertification. In this study, the effects

of novel mulches, PistachioPAM and PistachioPVAc, on changesin soil organic carbon and aggregate formation were investigatedto explore their potential uses for stabilizing the sand dunes in theDavaran plain (southeastern Iran). Furthermore, the effects of thesemulches on indicators of aggregate stability and fractal dimensionof the distribution of aggregate size were evaluated.

Materials and methods

Mulch design and production

The PistachioPAM and PistachioPVAc mulches were producedfrom the fresh residues of pistachio harvests. For this purpose,the coarser materials such as leaves were first separated from theresidues and were excluded. The remaining materials, which mainlyincluded pistachio peels, were then chopped into small pieces(< 2 mm). The chopped residues were added to the polymer–watersolutions with a ratio of 300 g residues per litre. Some physical andchemical properties of the mulches, including electrical conductiv-ity (EC) (Klute, 1986), pH (Richards, 1954), total nitrogen (Brem-ner, 1965), total phosphorus (Gupta & Mukerj, 2002), potassium(Helmek & Sparks, 1996), iron, zinc, copper and manganese (usingatomic absorption Awanta, model 932 GBC Scientific EquipmentLtd, Dandenong, Australia; Lindsay & Norvell, 1978), and watercontent were then measured (Table 1). The organic matter contentsof mulches were measured under dry (after drying at 65∘C) and wetconditions (Nelson & Sommers, 1986).

Soil sampling location and properties

To evaluate the effects of PistachioPAM and PistachioPVAcmulches on aggregate formation and soil surface stabilization,soil samples were taken from sand dunes in the Davaran plain(30∘45′ to 30∘50′ and 55∘45′ to 56∘24′) located around the cityof Rafsanjan, southeastern Iran (Figure 1). The samples were thenpassed through a 2-mm sieve, and their physical and chemicalproperties were determined on the fine fraction (< 2 mm) (Table 2).

Organic carbon content and microbial respiration ratemeasurements

For the soil organic carbon (SOC) content and microbial respirationrate (MRR) analyses, the soil samples were placed into plasticcontainers (20 cm× 15 cm× 5 cm) and the mulches were sprayed onto the surface of the samples at a rate of 1.5 l m−2 (this optimum ratiowas determined after various laboratory and field experiments). Atotal of 54 samples were prepared that included mulch treatmentsat three levels (i.e. PistachioPAM, PistachioPVAc and control), timein six levels (i.e. 2, 4, 8, 11, 15 and 19 weeks), and three replicates.To investigate the effects of environmental factors such as sunlight,temperature, rainfall and length of time required for treatment undernatural conditions, a control site outside the laboratory was setup. During the experiment, SOC contents of the treated sampleswere measured by the Walkley–Black method (Nelson & Sommers,1986). For the MRR measurement, 20 g of soil from the treated

© 2017 British Society of Soil Science, European Journal of Soil Science, 68, 783–791

Aggregation in stabilized sand dunes 785

Table 1 Physical and chemical characteristics of the mulches investigated

EC Moisture Wet OM Dry OM N P K Fe Zn Cu Mn

Mulch pH / dS m−1 / % / mg kg−1

PistachioPAM 5.43 7.23 93.00 1.50 22.30 3.80 0.140 3.24 652 0.45 10.0 34.0PistachioPVAc 5.06 11.30 86.00 3.66 25.60 2.70 0.150 3.45 751 0.50 8.80 41.70

Mn, manganese; Cu, copper; Zn, zinc; Fe, iron; K, potassium; N, nitrogen; EC, electrical conductivity; OM, organic materials.

Figure 1 Study area (Davaran plain in Kerman province, southeastern Iran)and an example of its sand dunes.

Table 2 Some physical and chemical properties of the soil used

ECHygroscopichumidity SOC Sand Clay Silt CaCO3Soil

texture pH / dS m−1 / %

Sandy 7.76 0.91 1.42 0.02 92 1 7 8

SOC, soil organic carbon; EC, electrical conductivity.

samples of each replicate were placed in a glass container, andthen the containers were incubated at 30± 1∘C. The soil moisturecontent was maintained at a constant amount. The CO2 producedby microbial respiration was collected in NaOH (0.1 mol l−1) for3 days. Subsequently, the MRR was determined with the Anderson

(1982) method by titration with HCl (0.1 mol l−1), and finally theCO2 (μg) released was calculated.

Measurement of aggregate stability

To evaluate the effects of PistachioPAM and PistachioPVAcmulches on soil aggregation, dry aggregate stability was mea-sured on three replicates at six different times: 2, 4, 8, 11, 15 and19 weeks from the beginning of the experiment. For this purpose,the samples were passed through a 4-mm sieve at the end of eachtime period. Following this, aggregate stability was measuredwith a rotating sieve device that comprised a series of sieves withdiameters of 0.1, 0.25, 0.5, 1.0 and 2.0 mm (according to theASTM standard). Shaking time for each sample was 3 minuteswith a horizontal rotational speed of 733 cHz. Finally, the meanweight diameter (MWD) of aggregates was calculated as theaggregate stability index with the following equation (Kemper &Rosenau, 1986):

MWD =n∑

i=1

wiXi, (1)

where Xi is the arithmetic mean diameter of each size fraction(mm) and wi is the proportion of total water-stable aggregates in thecorresponding size fraction. The wi is calculated after deducting thesand particles by dispersing and passing through the same sieve asindicated above.

Soil micromorphology analysis

To explore the possibility of aggregate formation after the addi-tion of PistachioPAM and PistachioPVAc mulches to the soil,micromorphological analyses were carried out. For this procedure,aggregate samples from the different treatments were selected andair-dried. Subsequently, the samples were saturated with Vespatulresin (Isofetalic). When the samples had hardened, they were cutout, the surface was smoothed with a soft powder of corundum,and the samples were fixed on glass slides. The surface of the sam-ples was then pulverized with coarse corundum powder and finallypolished with soft powders to obtain a thickness of 30 μm. Severalphotographs were taken from these prepared slides with a polar-izing microscope (HP–PL20T–PL20RT model, BW Optics Co.,Nanjing, China). The photographs were interpreted following theinstructions provided by Stoops (2003).



Measurement of fractal dimension

In this study, we used the model of Yang et al. (1993) to measure thefractal dimension of the aggregates that formed with the addition ofthe mulches investigated:

Mr<Ri

MT

=(

Ri

Rmax

)3−D

, (2)

where Mr<Ri is cumulative mass of soil particles from the smallestclass to the class i, MT is total mass of soil particles, Ri is particlediameter (mm) in class i, Rmax is the largest particle diameter inthe largest class and D is fractal dimension of the particle. Takingthe common logarithm of both sides of the equation, the followinglinear relation is obtained:

log10

(Mr<Ri

MT

)= 3 − D log10

(Ri

Rmax

). (3)

The fractal dimension is extracted from the slope of the line.

Statistical analysis

For each trial, a total of 54 samples were analysed with a completelyrandomized two-way anova, with three levels of mulch (i.e.PistachioPAM, PistachioPVAc and control) and six levels of time(i.e. 2, 4, 8, 11, 15 and 19 weeks). The analyses were carried outusing three replicates for each treatment combination of mulch andtime. When there was a significant effect, the means were comparedwith the least significant difference (LSD) test (𝛼 = 0.01). Thepartial correlation (PC) analysis was used to assess the independenteffect of each soil property (SOC, MRR and MWD) on aggregatefractal dimension. The PC is a measure of the strength anddirection of a linear relation between two continuous variableswhile controlling for the effect of one or more other continuousvariables. If necessary, prior to anova and PC analysis, the datawere transformed to meet the criteria of normality and homogeneityof the residuals. All analyses were performed with the Minitab Inc.,State College, PA, USA.

Figure 2 Mean comparison of mulch effects on the soil organic carboncontent. The standard error and least significant difference (LSD) from theanalysis of variance are given in the upper right-hand corner.

Results and discussion

Effects of mulch on soil organic carbon content and rateof microbial respiration

The results from the analysis of our data for the measured SOC andMRR are given in Table 3. The effects of treatments on SOC andMRR were statistically significant (P< 0.01). The largest organiccarbon content was in the samples stabilized by PistachioPVAc;the mean organic carbon content increased from 0.03% in thecontrol samples to 0.85% in the treated samples (Figure 2). Thisincrease in the SOM content with the addition of the PistachioPVAcmight be attributed to the larger amounts of organic material in thestructure of PistachioPVAc mulch than in that of PistachioPAMmulch. Overall, the large amount of the organic material in thestructure of both mulches has beneficial effects on soil physicaland chemical properties. This is true, especially in arid and semiarid regions where soil organic matter content is very small. Similarresults have also been reported by Sanchez-Martin et al. (2007) andBastida et al. (2008) on the effect of organic components on the soilorganic carbon content in soil.

The effect of PistachioPAM and PistachioPVAc mulches on theMRR is shown in Figure 3. The largest MRR was obtained in

Table 3 Analysis of variance results displaying the effects of PistachioPAM and PistachioPVAc mulches on the soil organic carbon content, microbialrespiration rate, mean weight diameter of aggregates and the fractal dimension of aggregates formed

Soil organiccarbon content / %

Microbial respirationrate / μg Co2 day−1 g−1 soil)

Mean weightdiameter / mm Fractal dimension

Source ofvariation DF SS MS F P SS MS F P SS MS F P SS MS F P

Mulch 2 7.2 3.51 125 <0.001 2344 1172 19.5 0.001 15.82 1172 561 0.001 1.04 0.517 506 <0.001Time 5 0.03 0.006 0.2 0.96 1531 306 5.10 0.001 0.95 306 13.4 <0.001 0.04 0.007 6.78 <0.001Mulch × time 10 0.21 0.02 0.77 0.66 790 79.1 1.32 0.26 0.75 79.1 5.35 <0.001 0.04 0.004 3.62 0.002Error 34 0.95 0.03 – – 2043 60.1 – – 0.48 60.1 – – 0.04 0.001 – –Total 53 8.41 – – – 6768 – – – 18.01 – – – 1.14 – – –CV – – 0.31 – – – 0.44 – – – 0.16 – – – 0.01 – –

DF, degrees of freedom; SS, sum of squares; MS, mean sum of squares; F, F statistic; P, probability; CV, coefficient of variation.



30

LSD1%= 6.99LSD1%=9.88

LSD1%=0.127

LSD1%=0.040

LSD1%= 0.090

LSD1%= 0.029

25

20

Mic

robi

al r

espi

rati

on /

μg

CO

2 5g

–1 s

oil h

–1

15

10

5

0

35

30

25

20

Mic

robi

al r

espi

rati

on /

μg

CO

2 5g

–1 s

oil h

–1

15

10

5

02 4 8 11 15 19

2.0

1.5

1.0

0.5

0.0

3.0

2.8

2.6

2.4

PistachiopVAc PistachioPAM

Treatment Time / week

2 4 8 11 15 19

Time / week

2 4 8 11 15 19

Time / week

MW

D /

mm

1.5

1.0

0.5

0.0

MW

D /

mm

Fra

ctal

dim

ensi

on

3.1

3.0

2.9

2.8

2.7

2.6

2.5

Fra

ctal

dim

ensi

on

control


Treatment

control


Treatment

control

(a) (d)

(b)

(c)

(e)

(f)

Figure 3 Mean comparison of the effects of mulches and time on different properties investigated. Effects of mulches on (a) rate of microbial respiration,(b) aggregate stability index (mean weight diameter, MWD) and (c) fractal dimension of the aggregates, and effects of time on (d) rate of microbial respiration,(e) aggregate stability index and (f) fractal dimension of the aggregates. The standard errors and least significant difference (LSD) values from the analysis ofvariance are given in the upper right-hand corners.

the soil treated with the mulches, whereas the smallest value wasobserved in the control. Therefore, it appears that spraying bothmulches has improved microbial respiration. For example, MRRincreased by 181% in the presence of PistachioPVAc comparedwith the control, whereas an increase of 137% in MRR wasobtained in the soil treated with the PistachioPAM. Differences inMRR among the treatments might result from the organic carboncontents of the mulches. By increasing SOC, the substrate requiredfor heterotrophic microbial populations increased and inevitably

enhanced the microbial population. Anderson (2003) stated thatthe rate of soil microbial respiration has a direct relation with theamount and quality of organic carbon added to soil, and showedthat MRR would reduce in the areas where fresh organic materialsare added in small quantities. Piotrowska et al. (2012) showed thatthe addition of biocomponents to soil increased the CO2 emissioncompared with that of the control soil within 24 hours.

Furthermore, the rate of CO2 production in the soil treated withthe two mulches was large at the beginning of the experiment



Figure 4 Images (scale, 100 μm) of the thin sections obtained from the aggregate samples formed with the addition of the mulches investigated (right column,PistachioPVAc; left column, PistachioPAM) at different times during the experiment (2, 8 and 19 weeks).

(see Figure 3). This rate decreased over time and then increased atweek 19. The largest rate of CO2 produced was about 23 μg-CO2

day−1 g−1 soil, which was related to the treated samples of weeks2, 5 and 19. The large rates of CO2 emission of these samples werethe result of rain and higher humidity than in weeks 8, 11 and 16when there was no rain.

Effects of mulch on the aggregate stability index

The addition of PistachioPVAc and PistachioPAM mulches tothe soil increased the MWD more than that of the control treat-ment (without mulch). The statistical analysis showed that theeffects of mulches, times and their interactions (i.e. mulch× time)are significant (P< 0.01) (Table 3). A comparison of the means

showed that the smallest and the largest MWD values wererelated to the control (MWD= 0.06 mm) and PistachioPVAc(MWD= 1.38 mm) treatments, respectively (Figure 3). Sprayingthe mulches on to the soil appears to have resulted in physicaland mechanical connections among components of the mulchesand the soil particles. This resulted in an interconnection ofindividual particles and the formation of large aggregates, andthus a wind-resistant layer on the soil surface. The images of thethin sections prepared of the treated samples in the soil micro-morphology analysis show how individual particles in the soilare bound together (see Figure 4). Within 2 weeks of sprayingthe mulch, organic compounds in the mulches were observedsporadically in some parts of the slides connecting the soil par-ticles like a bridge. The photographs taken at this time (i.e. at



2 weeks) confirm the initiation and progression of aggregation(see Figure 4). After 8 weeks of the experiment, individual soilparticles were coated with a layer of organic compounds, whichcreated more surfaces for the connection of individual particles. Thepresence of quite stable aggregates indicated the effectiveness of thetreatments (i.e. PistachioPVAc and PistachioPAM) (see Figure 4).

After 19 weeks, the pores were filled with organic compounds,which caused a reduction in the size of pores and thus an increasein the connectivity of the coarse particles. These observations alsosuggested that the formation of aggregates occurred together withthe creation of pores during the aggregation processes in the pres-ence of the mulches studied (see Figure 4). Aggregate formationimproved much more in the soil treated with PistachioPVAc thanin that treated with PistachioPAM. Moreover, the indirect effectsof other soil and mulch properties (such as pH, EC and calciumcarbonates) on aggregate stability should be considered becausethey might affect multivalent cations. These can also act as bridgesbetween organic colloids and soil particles, and thus improve soilaggregation and stability. The direct effects of organic components,however, on soil aggregation are more important and noticeable.Razafimbelo et al. (2006) stated that the differences in aggregationprocesses might be related to the larger amount of organic carbon.Karimi et al. (2012) reported that with the increase in the amount oforganic residuals, geometric and mean weighted diameter of aggre-gates (i.e. GMD and MWD) increased.

Comparison of the mean weight diameter of aggregates at thedifferent times in the experiment indicated an increase in aggregatestability over the time (Figure 3). The MWD value reached 0.93 mmin week 19 from 0.54 mm in the second week (increased by 1.7times). Therefore, the effects of mulches on the stability andadherence of aggregates were quite substantial at all times. Inother words, because of the lack of adhesion between particlesand absence of aggregates under natural conditions, addition of thePistachioPAM and PistachioPVAc mulches to the soil caused thebonding between fine particles to form larger aggregates. Therefore,the key role of these mulches was first to protect aggregates againstthe external forces (like a physical barrier) and second to act asnuclei for the formation of mineral–organic bonds.

The interaction between mulch and time (mulch× time) showedthat the mean diameter of aggregates formed that resulted fromthe addition of PistachioPVAc increased from 0.91 to 1.58 mm andfrom 0.65 to 1.15 mm in the presence of PistachioPAM (Figure 3).The greater MWD of the aggregates formed in the presence ofPistachioPVAc indicates the creation of more stable aggregates. Alarge percentage of the aggregate stability can be attributed to largeamounts of organic material and thus greater soil microbial activity,which helps the formation of stable aggregates. In addition, theeffect of PistachioPAM on the aggregation and formation of bondsbetween soil particles was different from that of PistachioPVAc.PistachioPAM was effective in increasing aggregate stability and inpreventing further destruction of the aggregates. In similar studies,Rachid et al. (2001) and Castro et al. (2002) also suggested thatcomponents of soil organic matter have a major effect on aggregatestability.

(a)

(b)

Figure 5 Comparison of the average effects of PistachioPVAc and Pista-chioPAM on the (a) aggregate stability index (mean weight diameter, MWD)and (b) fractal dimension at different times during the experiment. The stan-dard errors and least significant difference (LSD) values from the analysisof variance are given in the upper right-hand corners.

Effects of mulch on the soil fractal dimension index

The effects of mulch type, time and their interactions(i.e. mulch× time) on the fractal dimension of aggregates formedwere statistically significant (P< 0.01) (Table 3). The fractaldimension varied from 2.64 for the PistachioPVAc to 2.97 for thecontrol, but never passed the value of the upper limit of 3 (Figure 5).As was expected from fractal theory, the use of PistachioPAM andPistachioPVAc mulches had effects on the fractal dimension, andaggregates that formed in the presence of PistachioPVAc hadthe smallest fractal dimension. Moreover, images obtained fromthe thin sections revealed that the addition of PistachioPAM andPistachioPVAc mulches bonded soil particles together with bridgesbetween them (see Figure 4). This creates coarse aggregates andreduces their fractal dimension. The larger fractal dimension fromthe results of dry sieving showed that a large number of unstableaggregates were crushed into finer aggregates after sieving andthe number of fine aggregates increased. Sepaskhah et al. (2000)compared the number–size and mass–size fractal dimensions as ameasure of aggregate stability; they observed decreases in fractaldimension in soil treated with mulch.

Figure 3 shows that the fractal dimension decreased with timeduring the experimental period. The micromorphology analy-sis shows that the addition of PistachioPVAc and PistachioPAMmulches led to an increase in aggregate diameter and relative



Table 4 The partial correlation coefficients between the measured proper-ties and the fractal dimension of aggregates

Property

Soilorganiccarbon/ %

Microbialrespirationrate / μg CO2

day−1 g−1 soil

Mean weightdiameter ofaggregates/ mm

Microbial respiration rate(MRR) / μg CO2 day−1

g−1 soil

0.58 – –

Mean weight diameter ofaggregates (MWD) / mm

0.82 0.46 –

Fractal dimension (FD) −0.08 −0.47 −0.99

abundance of stable soil particles. This, in turn, reduced theaggregate fractal dimension after 5 months from the beginning ofthe trials (Figure 3). This is because of the presence of cementingagents that resulted from breakdown of the organic compounds bymicroorganisms. The organic materials formed bonding bridgesbetween larger particles and filled the large pores among the sandparticles. This resulted in a considerable reduction in aggregatefractal dimension over the time of the trial. These results suggestthat the fractal dimension can be used to explain the spatial andtemporal variation in soil structure as well as aggregate stability.

To analyse the independent effects of properties investigated(i.e. SOC, MRR and MWD) on aggregate fractal dimension, thepartial correlations were determined (Table 4). The results indicatethat there is a significant (r= 0.58, significant at P< 0.01) posi-tive correlation between the MRR and SOC. Jia et al. (2005) alsofound a significant positive correlation between microbial respira-tion and SOC during various measurements over time, and statedthat MRR and consequently the decomposition of soil organic mat-ter increased with the increase in SOC. In addition, there was astrong correlation (r = 0.82, significant at P< 0.01) between theSOC and MWD. This suggests that organic carbon is a criticalfeature that affects aggregate stability and could be a fundamentalfactor in the process of soil aggregation. The reason is that organiccarbon components (e.g. carbohydrates) are one of the main bond-ing agents of soil particles that promote aggregate formation andimprove aggregate stability. These organic compounds decreasethe sensitivity of soil structure to destructive forces by creating ahydrophobic coating around aggregates. These results are consistentwith those of many other researchers (Green et al., 2007; Khazaeiet al., 2008; Onweremadu et al., 2010). Moreover, all the character-istics studied had a significant correlation (P< 0.01) with the fractaldimension of aggregates (see Table 4). The strongest negative cor-relations between the properties studied and fractal dimension wererelated to organic carbon and MWD. The fractal dimension wassensitive to soil processes and it decreased with aggregate break-down. In other words, soil structural stability and MWD decreasedwith an increase in the fractal dimension. The results of this studywere in accord with those reported by Su et al. (2004) and Filgueiraet al. (2006).

Conclusions

This study has shown that differences in the organic matter contentof the PistachioPAM and PistachioPVAc mulches added to thesoil were not significant during the 5-month experimental period.Furthermore, the rate of microbial respiration in the presenceof mulches decreased during the experiment. This represents areduction in microbial activity after the addition of mulches tothe soil surface and thus a decrease in the rate of decompositionof organic matter by soil microorganisms. Therefore, becauseof the lack of significant changes in soil organic matter anda significant reduction in microbial respiration throughout theexperiment (indicating no degradation over time), we conclude thatthe PistachioPVAc and PistachioPAM mulches could potentially bevery stable in the environment, which is important in terms of theireffects on the protection of soil against wind erosion.

The positive effect of the mulches investigated on aggregateformation and stability might lead to a reduction in wind erosionbecause stable aggregates at the soil surface can prevent the removalof soil particles by wind. Therefore, the use of these syntheticmulches might improve the physical quality of certain types of soiland help protect against wind erosion in arid and semiarid regions.However, more research on the effects of synthetic mulches on soilphysical and mechanical properties is suggested under different soiland climate conditions.

Finally, the study showed that the fractal dimension of aggregatesis more sensitive to temporal changes than the mean weight diam-eter of aggregates. Therefore, the fractal dimension index could beused to evaluate the effects of mulches on aggregate stability. Thefractal dimension of the aggregates could also facilitate the anal-ysis and quantification of the conditions of aggregate stability atdifferent spatial or temporal scales or both.

References

Ahmadi, A., Neyshabouri, M.R., Rouhipour, H. & Asadi, H. 2011. Fractaldimension of soil aggregates as an index of soil erodibility. Journal of

Hydrology, 400, 305–311.Amiraslani, F. & Dragovich, D. 2011. Combating desertification in Iran

over the last 50 years: an overview of changing approaches. Journal of

Environmental Management, 92, 1–13.Anderson, J.P.E. 1982. Soil respiration. In: Methods of Soil Analysis. Part 2,

Chemical and Microbiological Properties (ed. R.H. Miller), pp. 831–871.American Society of Agronomy, Madison, WI.

Anderson, T.H. 2003. Microbial eco-physiological indicators to assess soilquality. Agriculture, Ecosystems & Environment, 98, 285–293.

Bastida, F., Kandeler, E., Moreno, J.L., Ros, M., Garsia, C. & Hernandez,T. 2008. Application of fresh and composted organic wastes modifiesstructure, size and activity of soil microbial community under semiaridclimate. Applied Soil Ecology, 40, 318–329.

Bremner, J.M. 1965. Total nitrogen. In: Methods of Soil Aanalysis. Part 2,

Chemical and Microbial Properties (ed. C.A. Black), pp. 1049–1178.American Society of Agronomy, Madison, WI.

Castro, C., Lourenco, A., Guimaraes, M.D.F. & Fonseca, I.C.B. 2002.Aggregate stability under different soil management systems in a redlatosol in the state of Parana, Brazil. Soil & Tillage Research, 65, 45–51.



Filgueira, R.R., Fournier, L.L., Cerisola, C.I., Gelati, P. & Garcia, M.G.2006. Particle-size distribution in soils: a critical study of the fractal modelvalidation. Geoderma, 134, 327–334.

Goudie, A.S. & Middleton, N.J. 2006. Dust storm control. In: Desert Dustin the Global System (eds A. Goudie & N.J. Middleton), pp. 193–199.Springer Science & Business Media Academic Journals, Berlin.

Green, V.S., Stott, D.E., Cruz, J.C. & Curi, N. 2007. Tillage impacts on soilbiological activity and aggregation in a Brazilian cerrado oxisols. Soil &

Tillage Research, 92, 114–121.Gregory, A.S., Bird, N.R.A., Watts, C.W. & Whitmore, A.P. 2012. An

assessment of a new model of dynamic fragmentation of soil with testdata. Soil & Tillage Research, 120, 61–68.

Gupta, R. & Mukerj, K.G. 2002. Root exudates-biology. In: Techniquesin Mycorrhizal Studies (eds K.G. Mukerji, K. Manoharachary & B.P.Chamola), pp. 103–131. Kluwer Academic Publishers, Dordrecht.

Hagen, L.J. 2010. Erosion by wind: modeling. Encyclopedia of Soil Science,2, 1–4.

He, S., Qiu, L., Jiang, D., Lamusa, A., Liu, Z. & Luo, Y. 2008. Sand-fixingeffects of Caragana microphylla shrub in Horqin Sandy. Frontiers ofForestry in China, 3, 31–35.

Helmek, P.A. & Sparks, D.L. 1996. Lithium, sodium potassium, rubidiumand caesium. In: Methods of Soil Analysis. Part 3, Chemical Methods (edsR.W. Weaver, J.S. Angle & P.S. Bottomley), pp. 551–575. Soil ScienceSociety of America, Madison, WI.

Jahanjo, B. 2000. The Chemical Effect of Polyacrylamide on the Diffusion

and Soil Erosion Control in the Irrigation. MSc thesis, Faculty ofAgricultural, Tehran University, Tehran, Iran.

Jia, B.R., Zhou, G.S., Wang, Y.H., Yang, W.P. & Zhou, L. 2005. Partitioningroot and microbial contributions to soil respiration in Leymus Chinensis

population. Soil Biology & Biochemistry, 37, 653–660.Karimi, R., Homaee, M., Afzalina, S., Ruhipour, H. & Basirat, S. 2012.

Organic resource management: impacts on soil aggregate stability andother physic-chemical properties. Agriculture, Ecosystems & Environ-ment, 148, 22–28.

Kemper, W.D. & Rosenau, R.C. 1986. Aggregate stability and size distri-bution. In: Methods of Soil Analysis. Part 1, Physical and MineralogicalMethods (ed. A. Klute), pp. 425–442. American Society of Agronomy,Madison, WI.

Khazaei, A., Mossadeghi, M.R. & Mahboubi, A.A. 2008. The effectof experimental conditions, the amount of organic matter, clay andcalcium carbonate on soil aggregate mean weight diameter and ten-sile strength of some soils of Hamadan province. Isfahan. Journal ofScience and Technology of Agriculture and Natural Resources, 11,123–134.

Kim, D., Chin, M., Remer, L.A., Diehl, T., Bian, H., Yu, H. et al. 2017.Role of surface wind and vegetation cover in multi-decadal variations ofdust emission in the Sahara and Sahel. Atmospheric Environment, 148,282–296.

Klute, A. 1986. Methods of soil analysis. In: Physical and Mineralogical

Methods. Part 1, 2nd edn (ed. A. Klute), p. 1188. American Society ofAgronomy, Madison, WI.

Lindsay, W.L. & Norvell, W.L. 1978. Development of a DTPA soil testfor zinc, iron, manganese, and copper. Soil Science Society of AmericaJournal, 42, 421–428.

Lopez, M.V., Dios Herrero, J.M., Hevia, G.G., Gracia, R. & Buschiazzo,D.E. 2007. Determination of the wind-erodible fraction of soils usingdifferent methodologies. Geoderma, 139, 1–18.

Luna, L., Miralles, I., Miralles, M.C., Gispert, M., Pellegrini, S., Vignozzi,N. et al. 2016. Restoration techniques affect soil organic carbon, glomalinand aggregate stability in degraded soils of a semiarid Mediterraneanregion. Catena, 143, 256–264.

Mohammadi Moghaddam, T. 2008. Physico-chemical and sensory proper-

ties of pistachio green hulls marmalade. MSc thesis, Food Science andTechnology Department, Ferdowsi University of Mashhad Iran (abstractin English).

Movahedan, M., Abbasi, N. & Keramati, M. 2012. Wind erosion controlof soils using polymeric materials. Eurasian Journal of Soil Science, 2,81–86.

Nelson, D.W. & Sommers, L.P. 1986. Total carbon, organic carbon andorganic matter. In: Methods of Soil Analysis. Part 2, Agronomy Handbook(ed. A.L. Page), pp. 539–579. American Society of Agronomy, Madison,WI.

Onweremadu, E., Izuogu, O. & Akamigbo, F. 2010. Aggregation andpedogenesis of seasonally inundated soils of a tropical watershed. Chiang

Mai Journal of Science, 37, 74–84.Piotrowska, A., Dlugosz, J., Zamorski, R. & Bogdanowicz, P. 2012. Changes

in some biological and chemical properties of an arable soil treatedwith the microbial biofertilizer UGmaxPolish. Journal of EnvironmentalStudies, 21, 455–463.

Rachid, M., Saber, N., El-Brahli, A., Lahlou, S. & Bessam, F. 2001. Total,particulate organic matter and structural stability of a Calcixeroll soilunder different wheat rotations and tillage systems in a semiarid area ofMorocco. Soil & Tillage Research, 57, 225–235.

Razafimbelo, T., Barthes, B., Larre-Larrouy, M.C., Deluca, E.F., Laurent,J.Y., Cerri, C.C. et al. 2006. Effect of sugarcane residue managementon organic matter in a clayey Oxisol from southern Brazil. Agriculture,

Ecosystems & Environment, 115, 285–289.Richards, L.A. (ed.) 1954. Diagnosis and Improvement of Saline and

Alkali Soils, Agriculture Handbook No. 60. Soil and Water Conserva-tion Research Branch Agricultural Research Service, U.S. GovernmentPrinting Office, Washington, DC.

Sanchez-Martin, M.J., Garcia-Delgado, M., Lorenzo, L.F., Rodriguez-Cruz,M.S. & Arienzo, M. 2007. Heavy metals in sewage sludge amended soilsdetermined by sequential extractions as a function of incubation time ofsoils. Geoderma, 142, 262–273.

Sepaskhah, A., Moosavi, S. & Boersma, L. 2000. Evaluation of fractaldimensions for analysis of aggregate stability. Iran Agricultural Research,19, 99–114.

Stoops, G. 2003. Guidelines for Analysis and Description of Soil andRegolith Thin Sections. Soil Science Society of America, Madison, WI.

Su, Y.Z., Zhao, H.L., Zhao, W.Z. & Zhang, T.H. 2004. Fractal features of soilparticle size distribution and the implication for indicating desertification.Geoderma, 122, 43–49.

Yang, P.L., Luo, Y.P. & Shi, Y.C. 1993. Fractal feature of soil on expressionby mass distribution of particle size. Chinese Science Bulletin, 38,1896–1899.

Zezin, A.B., Mikheikin, S.V., Rogacheva, V.B., Zansokhova, M.F.,Sybachin, A.V. & Yaroslavov, A.A. 2015. Polymeric stabilizers forprotection of soil and ground against wind and water erosion. Journal of

Advances in Colloid and Interface Science, 4, 1–13.Zhang, J.Q., Zhang, C.L., Chang, C.P., Wang, R.D. & Liu, G. 2017.

Comparison of wind erosion based on measurements and SWEEPsimulation: a case study in Kangbao County, Hebei Province China. Soil& Tillage Research, 165, 169–180.


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