EffectofBiocharApplicationonPhysicochemicalandHydraulic ...downloads.hindawi.com/journals/ace/2020/4592092.pdfInthispaper,theeffectsofdifferentamountsofbiochar anddifferentparticlesizesonthephysicochemicaland

Research ArticleEffect of Biochar Application on Physicochemical and HydraulicProperties of Loess

Xiujuan Yang Henghui Fan Yuhang Du and Lu Zhang

College of Water Resources and Architectural Engineering Northwest AampF University Yangling Xianyang 712100 China

Correspondence should be addressed to Henghui Fan yt07nwsuafeducn

Received 1 November 2019 Revised 21 April 2020 Accepted 17 June 2020 Published 18 August 2020

Academic Editor Annan Zhou

Copyright copy 2020 Xiujuan Yang et alis is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Biochar is important for optimizing soil physical structure and improving soil water retention e saturated water capacitytest water repellency test and permeability coefficient test were used to study the effects of biochar additive amount (0 2 510 15 and 20 gkg) and particle size (gt2mm 2mmndash0075mm and lt0075mm) on the basic physicochemical and hydraulicproperties of loess e results showed that with the increase of biochar additive content the relative particle densitydecreased linearly (R2 0984) the plastic limit liquid limit and plasticity index increased (R2 0947 0991 and 0984respectively) the maximum dry density decreased (R2 0900) and the optimal water content and saturated water contentincreased gradually At the same time the soilrsquos pH increased (R2 0957) the soil water repellency decreased and the waterinfiltration became easier but the soilrsquos permeability coefficient (saturated water conductivity) decreased When the thebiochar particles size is smaller the soilrsquos water repellency and permeability coefficient reduced Studies had shown that theapplication of biochar makes the loess infiltrate easily seepage slowly and contain more water which improve the waterinfiltration characteristics and water retention capacity of loess

1 Introduction

Biochar refers to a kind of solid insoluble matter producedby the carbonization of agricultural and forestry wastes [1] Itshows strong adsorption has high activity and is a potentialsoil improver [2] Previous studies had shown that biocharhas the effect of improving soil quality changing soil bulkdensity and porosity increasing soil aggregate structure andimproving soil hydrodynamic effects [3ndash5] and has a sig-nificant impact on rainfall erosion [6] Biochar is alkalineand has a significant effect in acid soil improvement [7]Yanli et al [8] have proved that acidified biochar can ef-fectively reduce the pH value of soda saline soil Biochar alsoeffectively inhibits the accumulation of salt in the soil surface[9]

Most of the soil in the loess region of northwest China isloose and the water retention capacity of the soil is weakwhich makes more serious soil erosion in this area roughthe soil column experiment Tan et al [10] found that as thenanocarbon content increases the saturated mass water

content of the disturbed loess soil increases and the saturatedhydraulic conductivity decreases Xin-xiang et al [11] foundthat biochar can absorb and retain moisture Rui-peng et al[12] found that biochar can increase the infiltration capacityof anthrosol and reduce the infiltration capacity of aeoliansandy soil Liu et al [13] found that high intraporosity andan irregular shape of biochar can effectively improve thewater retention of sandy soils After the addition of biocharthe runoff yielding time can be delayed and the amount oferosion can be reduced but the role of biochar is relativelyweak [6] Ni found that by adding 10 (vv) of biochar theoptimum water content of soil increased from 12 to 17while the maximum dry density decreased from 1890 to1740 kgm3 [14] Garg proposed biochar as an alternative soilamendment in landfill cover and found that the presence ofbiochar increased soil water content and the increasedamount was almost the same over a wide range of suctionvalues [15] In summary it can be found that differentbiochar addition amounts and different particle sizes havesignificant effects on soil water characteristics

HindawiAdvances in Civil EngineeringVolume 2020 Article ID 4592092 7 pageshttpsdoiorg10115520204592092

In this paper the effects of different amounts of biocharand different particle sizes on the physicochemical andhydraulic properties of typical loess in semiarid areas werestudied by the saturated water content test water repellencytest and permeability coefficient experiment It is proposedto provide scientific basis for soil erosion and other aspects

2 Materials and Methods

21 Materials e loess used in this experiment was Q4loess taken from the loess terrace-like plain area of Yan-gling Shaanxi e soil depth is 05ndash15m and the soil isbrownish yellow with a uniform texture After collection thegrass roots and other debris were removed naturally airdried and crushed and then passed through a 2mm sievee relative density of the particles was 271 and the un-disturbed soilrsquos moisture content is 131 In addition thedry density of the natural Loess is 136 gcm3 and the voidratio is 098 e basic physical and chemical indicators ofsoil samples are shown in Table 1

e biochar was selected from the rice husk charcoalwhich was provided by Jinan Yihe Century Landscaping CoLtd e biochar had a relative density of 045 and a pH of1009 and was alkaline In the biochar pulverization samplethe particle group of gt2mm accounted for 1268 the graingroup of 2mmndash0075mm accounted for 8529 and theparticle group of lt075mm accounted for 203

22 Methods

221 Test Plan Soils were uniformly mixed with biochars atcontents of 0 gkg 2 gkg 5 gkg 10 gkg 15 gkg and 20 gkg for the purpose of studying the effect of different contentsof biochar on soil properties Soils were uniformly mixedwith gt2mm 2ndash0075mm and lt0075mm biochars for thepurpose of studying the effect of biochar particle size on soilproperties e prepared sample had a water content of190 (optimal moisture content of Yangling loess) and adry density of 138 gcm3 (close to the natural loessrsquos drydensity) 148 gcm3 and 158 gcm3 (the maximum ofYangling loess dry densitytimes 090 compaction)

222 Routine Tests e experiments include the particlerelative density test boundary moisture test compactiontest pH test and permeability coefficient test ese testswere carried out in accordance with the test methodsspecified in the Geotechnical Test Specification (SL237-1999) Among them the boundary water content test usedthe liquid-plastic limit combined measuring instrument thecompacting test used the light compacting instrument thepH test used the electric measuring method and the per-meability coefficient test used the variable water headmethod

223 Soil Water Repellency Test Soil water repellency re-fers to the fact that certain soils cannot be wetted by waterWhen water drops on the surface of the soil with waterrepellency the water droplets will stay on the surface of the

soil for a while ese water droplets are not infiltrated for along time and their resistance to wetting varies from hoursto weeks

In this paper the water repellency of soil was tested bythe drip penetration time method [16] According to the testscheme the homogeneous mixed soil samples with the sameinitial moisture content and different dry densities werepressed into cutting rings e distilled water droplets weresucked up on the surface of the soil sample by using a pipetteand the infiltration time from the contact of the waterdroplets with the surface of the soil to the complete pene-tration was recorded In order to reduce the influence ofkinetic energy of water droplets the distance between themouth of the drip tube and the surface of the soil sampleshould be controlled to about 1 cm Each soil sample wasrepeatedly measured 4 times at different positions and theaverage value of the complete infiltration time was taken asthe drip infiltration time of the soil sample

224 SoilWater Capacity Test Saturated water content alsoknown as saturated water capacity and water holding ca-pacity is the ratio of the mass of water to the mass of solidparticles when the soil pores are completely filled with waterexpressed as a percentage [17] e uniformly mixed soilsamples were pressed into three-axis molds according todifferent dry densities and placed them in a soil samplesaturators e soil sample was vacuum-saturated and thenflooded in water for 48 he soil sample was carefully takenout weighed and then dried and weighed for the purpose ofcalculating the saturated moisture content of the soil sampleree parallel samples were prepared for each soil sampleand the average value was taken as the saturated watercontent of the soil sample

3 Results and Analysis

31 Effect of Biochar Content on Physical Properties of SoilSamples Table 2 shows the relative particle density valuesranged from 271 to 220 for the 20 gkg biochar amendedsoil

e regression equation for relative particle density as afunction of the biochar amendment rate was determined asshown in the following equation

relative particle density minus0105 times(gkg biochar)

+ 2806 R2

09841113872 1113873(1)

It is clear that the relative particle density value rangesfrom 271 to 220 decreasing with increasing biochar contentfrom 0 gkg to 20 gkg is is due to differences in physicalproperties of biochar and soile relative density of biocharis 045 and when it is incorporated into the soil it occupies apart of the space of the particles As the proportion ofbiochar in the soil increases the amount of soil particlesdecreases relatively and the relative particle density ofbiochar mixed with soil decreases

e boundary water content of soil is an importantindicator for the division of soil state and the liquid plastic

2 Advances in Civil Engineering

limit of soil is often used as an indicator to assess soil erosionvulnerability and shallow surface movement [18] Unlike therelative particle density plastic limit increased with theapplication of biochar amendment e lowest plastic limitwas 2068 for the nonamended soil increasing to 20912096 2133 2173 and 2217 respectively eplastic limit is related to the rate of biochar amendment bythe following equation

plastic limit 0294 times(gkgbiochar) + 20269 R2

09471113872 1113873

(2)

Just like plastic limit the liquid limit and the plasticityindex are also related to the rate of biochar amendment bythe following equation

liquid limit 0827 times(gkgbiochar) + 35430 R2

09911113872 1113873

(3)

plasticity index 0533 times(gkgbiochar) + 15161 R2

09841113872 1113873

(4)

e regression equation in plastic limit reveals a sig-nificant increase as the rate of biochar amendment in-creased Equations (3) and (4) also demonstrate that theliquid limit and plasticity index have the same tendencyWith the increasing of biochar additive the fine particles inthe soil gradually increased e specific surface area of thebiochar is larger than the soil resulting in a larger range ofsoil water content in the plastic state And then the waterholding capacity is increased

e results of the compaction experiment (Figure 1)show that as the biochar content increases the compac-tion curve of the soil shifts to the right and the peakgradually decreases e maximum dry density of the soildecreased from 174 gcm3 to 166 gcm3 e optimummoisture content gradually increased from 190 to218 e linear decrease in maximum dry density as afunction of biochar application rate is represented by thefollowing

themaximumdry density minus0015 times(gkg biochar)

+ 1741 R2

09001113872 1113873(5)

And the linear increase in optimum moisture content asa function of biochar application rate is showed by thefollowing equation

the optimummoisture content 0630 times(gkg biochar)

+ 17749 R2

09421113872 1113873

(6)

Due to the incorporation of biochar the structure of thenonamended soil is looser than amended soil and it is noteasy to compact In this case the water holding capacity ofthe soil is enhanced

32 Effect of Biochar Content on pH Values Since biochar isrich in calcium and alkaline the application of biochar caneffectively regulate acid and is a very effective soil acidneutralizer [19] At the same time the long-term use ofbiochar can replace sodium ions to reduce the alkalizationhazard and has certain effects on the improvement of salinesoil and alkaline soil [20] In this test the time effect was notconsiderede pH value of the mixed soil sample was tested(Table 2)With the increase of the amount of biochar the pHvalue of the soil sample increases the equation is as follows

pH value 0016 times(gkgbiochar) + 8600 R2

09571113872 1113873

(7)

e regression equation reveals a significant increase inpH value as the rate of biochar amendment increases Whilethe overall range of the pH value is between 863 and 871the study in [8] found that acidified biochar can effectivelyreduce the pH value of soda saline-alkaline soil and alkalinebiochar also has the effect of lowering the pH value of salinesoil [21] In this test the pH of the biochar was 1009 and theloessrsquos pHwas 863 In short-term action the biochar did notwork on the soil so the results just represented the mixturersquospH not included the physicochemical action of the biochar

Table 2 Effect of biochar content on physical and chemical properties of soil

Biochar application (gkg) Relative particle density Plastic limit () Liquid limit () Plastic index pH value0 271 2068 3630 1562 8632 262 2091 3714 1623 8635 245 2096 3790 1694 86410 237 2133 3864 1731 86715 229 2173 3936 1763 86820 220 2217 4061 1844 871

Table 1 e parameters of the loess

Liquidlimit()

Plasticlimit()

Plasticityindex

Maximumdry density(gcm3)

Optimummoisturecontent()

Particle size ()

pHOrganicmatter(gkg)

Solublesalt (gkg)

Insolublesalt (gkg)2ndash0075mm 0075ndash0005mm lt0005mm

363 207 156 174 1903 081 7418 2501 863 506 016 8498

Advances in Civil Engineering 3

on the soil For long-term reactions follow-up experimentsare also required

33Effect ofBiocharContent onSaturatedMoistureContent ofSoil Samples Water holding capacity is one of the physicalproperties of the soil And the saturated water content is animportant index of the maximum water holding capacity ofsoil e relationship between the measured saturated watercontent of the soil and the biochar content the dry density ofthe soil is plotted in Figure 2 It can be seen that as the drydensity of the soil increases the saturated water contentdecreases e internal porosity reduces because of highdensity and thus the amount of stored water decreaseswhen saturated At the same time the curves of the saturatedwater content of soil with increasing dry density under theaction of different biochars are basically parallel It meansthat biochar application has a significant improvement inthe water retention capacity of the soil

34 Effect of Biochar Content and Particle Size on Soil WaterRepellency Soil water repellency is related to soil organicmatter water content pH temperature chemical compo-sition soil structure compactness and other factors [22 23]In this study the initial soil moisture content of the controlsoil was described and the relationship between water in-filtration time and biochar content was obtained using threedifferent dry density samples (Figure 3) Under the sameconditions the dry density has a greater impact on theinfiltration time Taking pure loess as an example the in-filtration time of water droplets increases linearly from 549 s(138 gcm3) to 688 s (158 gcm3) which is about 11 timesHowever this effect of dry density gradually decreases as theamount of biochar blending increases

With the increase of biochar addition the infiltrationtime of water droplets of all soil samples gradually decreasese greater the dry density of the soil sample the greater the

rate of decline It is generally believed that the soil with dripinfiltration time exceeds 5 s and the soil has water repellencyIf the drip infiltration time is 5ndash60 s the soil has slight waterrepellency if the drip infiltration time is 60ndash600 s the soilhas strong water repellency and if the drip infiltration timeis more than 3600 s the soil is considered to have extremewater repellency [24] It can be seen that when the soilsample is dense the water is difficult to infiltrate and the soilsample has strong water repellency After the biochar isadded the water repellency is gradually reduced When thesoil sample density is small the soil sample is changed fromslightly water repellent to nonwater repellent

For the aspect of biochar particle size when incorporatingcoarse-grained biochar the infiltration time of water dropletsis greater than the infiltration time of water droplets when

Original loessBiochar content = 2gkgBiochar content = 5 gkg

Biochar content = 10 gkgBiochar content = 15 gkgBiochar content = 20 gkg

Satu

rate

d m

oistu

re co

nten

t (

)

21

22

23

24

25

26

27

28

29

30

31

32

33

150 155 160 165 170 175145

Dry density (gcm3)

Figure 2 e variation of soil saturated moisture content

Dry

den

sity

(gc

m3 )

Original loessBiochar content = 2gkgBiochar content = 5gkg

Biochar content = 10gkgBiochar content = 15gkgBiochar content = 20gkg

150152154156158160162164166168170172174176

16 18 20 22 24 26 2814Moisture content ()

Figure 1 e variation of soil ρdmax and wop


mixed with fine-grained biochar It is indicated that the effectof coarse-grained biochar on soil water repellency should beimproved Compared with coarse-grained biochar fine-grained biochar is more likely to interact with soil particlesand form soil aggregates [25] which promotes an increase insoil porosity and reduces the water repellency of the soil

35 Effect of Biochar Content and Particle Size on SoilPermeability e permeability coefficient (saturated waterconductivity) of soil is directly related to the number ofpores in the soil the structure of the soil and the textureepermeability change of soil after adding biochar of differentcontents and particle sizes is shown in Figure 4 Under the

same conditions the dry density has a great influence on theinfiltration time With the increase of biochar addition thepermeability coefficient of soil gradually decreases indi-cating that biochar treatment significantly inhibited theinfiltration capacity of loess which is consistent with theresearch in [26] At the same time from the perspective ofbiochar particle size the coarse-grained biochar has a lowerpermeability to soil than the fine-grained biochar which isnot consistent with the studies in [27 28] is is due to thedifferent study objects used in the test e loess used in thetest is mainly composed of fine particles including very littlecalcareous sand e difference in particle size between thethree soils is significant so the conclusions are notconsistent

Infil

trat

ion

time (

s)

051015202530354045505560

138 gcm3 gt2mm138 gcm3 2mm ndash 0075mm138 gcm3 lt0075mm

5 10 15 200Biochar content (gkg)

(a)

Infil

trat

ion

time (

s)

2468

101214161820222426



(b)

Infil

trat

ion

time (

s)


10

20

30

40

50

60

70

80


(c)

Figure 3e variation of soil infiltration time with the amount of biochar (a) for ρ 138 gcm3 (b) for ρ 148 gcm3 and (c) for ρ 158 gcm3


4 Conclusions

Experimental results from this study show that biochar ad-dition has a positive impact on the physicochemical and hy-draulic properties of loess e relative density and maximumdry density of soil particles were significantly reduced bythe application of biochar However the soilrsquos alkali value theboundary moisture content the optimal water content and thesaturated water content of the soil were significantly improvedby biochar at all and also the water capacity of soil e soilrsquoshydrophobicity was reduced by the biochar and in this way itbecame easier for water penetration But the soilrsquos permeabilitycoefficient (saturated hydraulic conductivity) decreased In thiscase the water migrated slowly through the soil and the soilmaintained its enhanced water absorption capacity e hy-draulic properties of loess were affected by the added biochar

size When the size is larger the soilrsquos water repellency in-creased and it has a greater decrease in permeability coefficient

Data Availability

e data used to support the findings of this study areavailable from the first author upon request

Conflicts of Interest

e authors declare that there are no conflicts of interest

Acknowledgments

is research was financially supported by the YanglingScience and Technology Project (Grant no 2018NY-28) and

Perm

eabi

lity

coef

ficie

nt (lowast

10ndash6

cms

)



40

45

50

55

60

65

70

75

80

(a)

Perm

eabi

lity

coef

ficie

nt (lowast

10ndash6

cms

)



20

25

30

35

40

45

50

55

60

(b)

Perm

eabi

lity

coef

ficie

nt (lowast

10ndash6

cms

)



00

05

10

15

20

25

30

(c)

Figure 4 e variation of soil permeability coefficient (a) for ρ 138 gcm3 (b) for ρ 148 gcm3 and (c) for ρ 158 gcm3


the Natural Science Basic Research Plan in Shaanxi Provinceof China (Grant no 2020JQ-278)e authors also thank theShaanxi Postdoctoral Research Funding Project (Grant no2018BSHEDZZ23) And sincere thanks are due to LIUKaiming and JIANG Kai who devoted themselves in thisreport

References

[1] M J Antal andM Groslashnli ldquoe art science and technology ofcharcoal productiondaggerrdquo Industrial amp Engineering ChemistryResearch vol 42 no 8 pp 1619ndash1640 2003

[2] W I Woods N P S Falcatildeo W G Teixeira et al ldquoBiochartrials aim to enrich soil for smallholdersrdquo Nature vol 443no 7108 p 144 2006

[3] K Jindo M A Sanchez-Monedero T Hernandez et alldquoBiochar influences the microbial community structureduring manure composting with agricultural wastesrdquo Scienceof the Total Environment vol 416 pp 476ndash481 2012

[4] X H Liu F P Han and X C Zhang ldquoEffect of biochar on soilaggregates in the loess plateau results from incubation ex-perimentsrdquo International Journal of Agriculture and Biologyvol 14 no 6 pp 975ndash979 2012

[5] G S Pardo A K Sarmah and R P Orense ldquoMechanism ofimprovement of biochar on shear strength and liquefactionresistance of sandrdquo Geotechnique vol 69 no 6 pp 471ndash4802019

[6] W Yuan-yuan Y Ming-yi F-B Zhang et al ldquoEffect ofbiochar application on erodibility of plow layer on loessslopesrdquo Acta Pedologica Sinica vol 53 no 1 pp 81ndash92 2016

[7] M F Qayyum I Ashraf M Abid and D Steffens ldquoEffect ofbiochar lime and compost application on phosphorus ad-sorption in a Ferralsolrdquo Journal of Plant Nutrition and SoilScience vol 178 no 4 pp 576ndash581 2015

[8] Y Yan-li L Xiu-jun C Guo-shuang et al ldquoEffects of biocharon saline-sodic soil physical and chemical propertiesrdquo Soiland Crop vol 4 no 3 pp 113ndash119 2015

[9] S Yun-peng Y Jin-song R-J YAO et al ldquoBiochar andchemical fertilizer application on soil properties in farmlandreclaimed from salinity tidal flatrdquo Chinese Journal of SoilScience vol 48 no 2 pp 454ndash459 2017

[10] S TAN Z Bei-bei and Q-J WANG ldquoEffects on nano-carbonon water infiltration process in disturbed loessal soilrdquo ActaPedologica Sinica vol 51 no 2 pp 263ndash268 2014

[11] C Xin-xiang H Xu-sheng W ZHANG et al ldquoEffects ofquantity of biochar on nitrogen leaching in simulated soilcolumns and soil moisture parameters in fieldrdquo AgriculturalResearch in the Arid Areas vol 32 no 1 pp 110ndash114 2014

[12] Q I Rui-peng L ZHANG Y-H YAN et al ldquoEffects ofbiochar addition into soils in semiaris land on water infil-tration under the condition of the same bulk densityrdquo ChineseJournal of Applied Ecology vol 25 no 8 pp 2281ndash2288 2014

[13] Z L Liu B Dugan C A Masiello et al ldquoBiochar particle sizeshape and porosity act together to influence soil waterpropertiesrdquo PLoS One vol 12 no 6 Article ID e01790792017

[14] J J Ni X W Chen C W Ng and H W Guo ldquoEffects ofbiochar on water retention and matric suction of vegetatedsoilrdquo Geotechnique Letters vol 8 no 2 pp 124ndash129 2018

[15] A Garg S Bordoloi J Ni et al ldquoInfluence of biochar additionon gas permeability in unsaturated soilrdquo Geotechnique Lettersvol 9 no 1 pp 66ndash71 2019

[16] W Vanrsquot and D Bessel ldquoParticle coatings affecting thewettability of soilsrdquo Journal of Geophysical Research vol 64no 2 pp 263ndash267 1959

[17] L Jia-cheng Soil Agrochemical Analysis Handbook p 12China Agriculture Press Beijing China 1988

[18] S Stanchi M Freppaz and E Zanini ldquoe influence of Alpinesoil properties on shallow movement hazards investigatedthrough factor analysisrdquo Natural Hazards and Earth SystemSciences vol 12 no 6 pp 1845ndash1854 2012

[19] T Wang C E Stewart C Sun Y Wang and J ZhengldquoEffects of biochar addition on evaporation in the five typicalLoess Plateau soilsrdquo Catena vol 162 pp 29ndash39 2018

[20] J-H Yuan R-K Xu and H Zhang ldquoe forms of alkalis inthe biochar produced from crop residues at different tem-peraturesrdquo Bioresource Technology vol 102 no 3pp 3488ndash3497 2011

[21] W Zhang G Zeng-chao C Xin-xiang et al ldquoEffects ofbiochar on saline soil improvementrdquo Agricultural Research inthe Arid Areas vol 31 no 2 pp 73ndash77+105 2013

[22] Y Song J-HWU H-Y DONG et al ldquoSoil water repellency ofsands and clay as affected by particle sizerdquo Acta PedologicaSinica vol 53 no 2 pp 421ndash426 2016

[23] D Diehl ldquoSoil water repellency dynamics of heterogeneoussurfacesrdquo Colloids and Surfaces A Physicochemical and En-gineering Aspects vol 432 no 2 pp 8ndash18 2013

[24] J Letey M Carrillo and X Pang ldquoApproaches to characterizethe degree of water repellencyrdquo Journal of Hydrology vol 231-232 pp 61ndash65 2000

[25] H Herath M Camps-Arbestain and M Hedley ldquoEffect ofbiochar on soil physical properties in two contrasting soils anAlfisol and an Andisolrdquo Geoderma vol 209-210 pp 188ndash1972013

[26] X Qian W Li-mei Q Rui-peng et al ldquoEffects of biochar onwater infiltration and water holding capacity of loessial soilrdquoJournal of Earth Environment vol 7 no 1 pp 65ndash76+862016

[27] L Esmaeelnejad M Shorafa M Gorji and S m HosseinildquoImpacts of woody biochar particle size on porosity andhydraulic conductivity of biochar-soil mixtures an incubationstudyrdquo Communications in Soil Science and Plant Analysisvol 48 no 14 pp 1710ndash1718 2017

[28] A Ibrahim A R Usman M I Al-Wabel et al ldquoEffects ofconocarpus biochar on hydraulic properties of calcareoussandy soil influence of particle size and application depthrdquoArchives of Agronomy and Soil Science vol 63 2017


In this paper the effects of different amounts of biocharand different particle sizes on the physicochemical andhydraulic properties of typical loess in semiarid areas werestudied by the saturated water content test water repellencytest and permeability coefficient experiment It is proposedto provide scientific basis for soil erosion and other aspects

2 Materials and Methods

21 Materials e loess used in this experiment was Q4loess taken from the loess terrace-like plain area of Yan-gling Shaanxi e soil depth is 05ndash15m and the soil isbrownish yellow with a uniform texture After collection thegrass roots and other debris were removed naturally airdried and crushed and then passed through a 2mm sievee relative density of the particles was 271 and the un-disturbed soilrsquos moisture content is 131 In addition thedry density of the natural Loess is 136 gcm3 and the voidratio is 098 e basic physical and chemical indicators ofsoil samples are shown in Table 1

e biochar was selected from the rice husk charcoalwhich was provided by Jinan Yihe Century Landscaping CoLtd e biochar had a relative density of 045 and a pH of1009 and was alkaline In the biochar pulverization samplethe particle group of gt2mm accounted for 1268 the graingroup of 2mmndash0075mm accounted for 8529 and theparticle group of lt075mm accounted for 203

22 Methods

221 Test Plan Soils were uniformly mixed with biochars atcontents of 0 gkg 2 gkg 5 gkg 10 gkg 15 gkg and 20 gkg for the purpose of studying the effect of different contentsof biochar on soil properties Soils were uniformly mixedwith gt2mm 2ndash0075mm and lt0075mm biochars for thepurpose of studying the effect of biochar particle size on soilproperties e prepared sample had a water content of190 (optimal moisture content of Yangling loess) and adry density of 138 gcm3 (close to the natural loessrsquos drydensity) 148 gcm3 and 158 gcm3 (the maximum ofYangling loess dry densitytimes 090 compaction)

222 Routine Tests e experiments include the particlerelative density test boundary moisture test compactiontest pH test and permeability coefficient test ese testswere carried out in accordance with the test methodsspecified in the Geotechnical Test Specification (SL237-1999) Among them the boundary water content test usedthe liquid-plastic limit combined measuring instrument thecompacting test used the light compacting instrument thepH test used the electric measuring method and the per-meability coefficient test used the variable water headmethod

223 Soil Water Repellency Test Soil water repellency re-fers to the fact that certain soils cannot be wetted by waterWhen water drops on the surface of the soil with waterrepellency the water droplets will stay on the surface of the

soil for a while ese water droplets are not infiltrated for along time and their resistance to wetting varies from hoursto weeks

In this paper the water repellency of soil was tested bythe drip penetration time method [16] According to the testscheme the homogeneous mixed soil samples with the sameinitial moisture content and different dry densities werepressed into cutting rings e distilled water droplets weresucked up on the surface of the soil sample by using a pipetteand the infiltration time from the contact of the waterdroplets with the surface of the soil to the complete pene-tration was recorded In order to reduce the influence ofkinetic energy of water droplets the distance between themouth of the drip tube and the surface of the soil sampleshould be controlled to about 1 cm Each soil sample wasrepeatedly measured 4 times at different positions and theaverage value of the complete infiltration time was taken asthe drip infiltration time of the soil sample

224 SoilWater Capacity Test Saturated water content alsoknown as saturated water capacity and water holding ca-pacity is the ratio of the mass of water to the mass of solidparticles when the soil pores are completely filled with waterexpressed as a percentage [17] e uniformly mixed soilsamples were pressed into three-axis molds according todifferent dry densities and placed them in a soil samplesaturators e soil sample was vacuum-saturated and thenflooded in water for 48 he soil sample was carefully takenout weighed and then dried and weighed for the purpose ofcalculating the saturated moisture content of the soil sampleree parallel samples were prepared for each soil sampleand the average value was taken as the saturated watercontent of the soil sample

3 Results and Analysis

31 Effect of Biochar Content on Physical Properties of SoilSamples Table 2 shows the relative particle density valuesranged from 271 to 220 for the 20 gkg biochar amendedsoil

e regression equation for relative particle density as afunction of the biochar amendment rate was determined asshown in the following equation

relative particle density minus0105 times(gkg biochar)

+ 2806 R2

09841113872 1113873(1)

It is clear that the relative particle density value rangesfrom 271 to 220 decreasing with increasing biochar contentfrom 0 gkg to 20 gkg is is due to differences in physicalproperties of biochar and soile relative density of biocharis 045 and when it is incorporated into the soil it occupies apart of the space of the particles As the proportion ofbiochar in the soil increases the amount of soil particlesdecreases relatively and the relative particle density ofbiochar mixed with soil decreases

e boundary water content of soil is an importantindicator for the division of soil state and the liquid plastic




09471113872 1113873

(2)



09911113872 1113873

(3)


09841113872 1113873

(4)




+ 1741 R2

09001113872 1113873(5)



+ 17749 R2

09421113872 1113873

(6)




09571113872 1113873

(7)





Liquidlimit()

Plasticlimit()

Plasticityindex



Particle size ()


Solublesalt (gkg)


363 207 156 174 1903 081 7418 2501 863 506 016 8498










Satu

rate

d m

oistu

re co

nten

t (

)

21

22

23

24

25

26

27

28

29

30

31

32

33

150 155 160 165 170 175145

Dry density (gcm3)


Dry

den

sity

(gc

m3 )



150152154156158160162164166168170172174176







Infil

trat

ion

time (

s)

051015202530354045505560



(a)

Infil

trat

ion

time (

s)

2468

101214161820222426



(b)

Infil

trat

ion

time (

s)


10

20

30

40

50

60

70

80


(c)



4 Conclusions



Data Availability




Acknowledgments


Perm

eabi

lity

coef

ficie

nt (lowast

10ndash6

cms

)



40

45

50

55

60

65

70

75

80

(a)

Perm

eabi

lity

coef

ficie

nt (lowast

10ndash6

cms

)



20

25

30

35

40

45

50

55

60

(b)

Perm

eabi

lity

coef

ficie

nt (lowast

10ndash6

cms

)



00

05

10

15

20

25

30

(c)




References
































09471113872 1113873

(2)



09911113872 1113873

(3)


09841113872 1113873

(4)




+ 1741 R2

09001113872 1113873(5)



+ 17749 R2

09421113872 1113873

(6)




09571113872 1113873

(7)





Liquidlimit()

Plasticlimit()

Plasticityindex



Particle size ()


Solublesalt (gkg)


363 207 156 174 1903 081 7418 2501 863 506 016 8498










Satu

rate

d m

oistu

re co

nten

t (

)

21

22

23

24

25

26

27

28

29

30

31

32

33

150 155 160 165 170 175145

Dry density (gcm3)


Dry

den

sity

(gc

m3 )



150152154156158160162164166168170172174176







Infil

trat

ion

time (

s)

051015202530354045505560



(a)

Infil

trat

ion

time (

s)

2468

101214161820222426



(b)

Infil

trat

ion

time (

s)


10

20

30

40

50

60

70

80


(c)



4 Conclusions



Data Availability




Acknowledgments


Perm

eabi

lity

coef

ficie

nt (lowast

10ndash6

cms

)



40

45

50

55

60

65

70

75

80

(a)

Perm

eabi

lity

coef

ficie

nt (lowast

10ndash6

cms

)



20

25

30

35

40

45

50

55

60

(b)

Perm

eabi

lity

coef

ficie

nt (lowast

10ndash6

cms

)



00

05

10

15

20

25

30

(c)




References






































Satu

rate

d m

oistu

re co

nten

t (

)

21

22

23

24

25

26

27

28

29

30

31

32

33

150 155 160 165 170 175145

Dry density (gcm3)


Dry

den

sity

(gc

m3 )



150152154156158160162164166168170172174176







Infil

trat

ion

time (

s)

051015202530354045505560



(a)

Infil

trat

ion

time (

s)

2468

101214161820222426



(b)

Infil

trat

ion

time (

s)


10

20

30

40

50

60

70

80


(c)



4 Conclusions



Data Availability




Acknowledgments


Perm

eabi

lity

coef

ficie

nt (lowast

10ndash6

cms

)



40

45

50

55

60

65

70

75

80

(a)

Perm

eabi

lity

coef

ficie

nt (lowast

10ndash6

cms

)



20

25

30

35

40

45

50

55

60

(b)

Perm

eabi

lity

coef

ficie

nt (lowast

10ndash6

cms

)



00

05

10

15

20

25

30

(c)




References

































Infil

trat

ion

time (

s)

051015202530354045505560



(a)

Infil

trat

ion

time (

s)

2468

101214161820222426



(b)

Infil

trat

ion

time (

s)


10

20

30

40

50

60

70

80


(c)



4 Conclusions



Data Availability




Acknowledgments


Perm

eabi

lity

coef

ficie

nt (lowast

10ndash6

cms

)



40

45

50

55

60

65

70

75

80

(a)

Perm

eabi

lity

coef

ficie

nt (lowast

10ndash6

cms

)



20

25

30

35

40

45

50

55

60

(b)

Perm

eabi

lity

coef

ficie

nt (lowast

10ndash6

cms

)



00

05

10

15

20

25

30

(c)




References






























4 Conclusions



Data Availability




Acknowledgments


Perm

eabi

lity

coef

ficie

nt (lowast

10ndash6

cms

)



40

45

50

55

60

65

70

75

80

(a)

Perm

eabi

lity

coef

ficie

nt (lowast

10ndash6

cms

)



20

25

30

35

40

45

50

55

60

(b)

Perm

eabi

lity

coef

ficie

nt (lowast

10ndash6

cms

)



00

05

10

15

20

25

30

(c)




References































References






























Documents

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