THE IMPACT OF CARBONATE MINERALS CONTENT ON SOIL PORE SIZE DISTRIBUTION

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1 I.J.S.N., VOL.9 (2) 2018: ISSN THE IMPACT OF CARBONATE MINERALS CONTENT ON SOIL PORE SIZE DISTRIBUTION 1 Namee T. Mahdi & 2 Hasan S. Naji 1 Dept. of Desetification Combat, College of Agicultue-Univesity of Baghdad, Iaq 1 Dept. of Soil Science and Wate Resouces, College of Agicultue-Univesity of Baghdad, Iaq Coesponding autho Namee.Taha@yahoo.com ABSTRACT The poosity and poe space of soil as well as poe size distibution is an impotant facto fo soil hydaulic conductivity and wate etention. This study includes an expeimental investigation of the effect of cabonate mineals on poe size distibution. Soil mateial with loam textue was used to pepae nine soil mateials containing wide ange of cabonate mineals ( gm kg -1 ). The soil-wate etention cuve (θ(ψ)) was estimated. Compute pogam (RETC code) was used to detemine the best-fit fo expeimental data of wate potential vesus volumetic wate content which have nonlinea elationship to detemine the paamete of van Genuchten equation [α, n and m with m=1-(1/n)]. The capillay ise equation ( young-laplace equation) was used to estimate the effective poe diamete (D). The es ults show that poe space was affected by cabonate mineals contents. Ai poes (> 30μm) inceased 1.4 fold with inceasing cabonate mineals at the same time capillay poes filled with wate (< 30μm) deceased by 1.3 folds. The elative of wate volume to total soil volume anged between 0.27 and 0.21 cm 3 cm -3 fo cabonate mineals content 3.2 and 352 g kg -1 espectively. At 10 Kps the amount of wate lost inceased with inceasing cabonate mineals content, whee soil sample with 352 g.kg 1 cabonate mineals lost wate moe than soil sample with 3.2 gm.kg -1 cabonate mineals by 42%. The pecentage of poes (<30 μm) anged fom 67% to 79% and the poes (>30 μm) anged fom 33% to 21%. In conclusion, the high cabonate mineals content in the soil led to change in poe size distibution, whee ai-filled poes inceased and capillay poes filled with wate (wate holding capacity) deceased at diffeent degee fom sample to anothe. KEYWORD: Wate etention cuves, Young-Laplace equation, effective poe diamete, void atio. INTRODUCTION Soil contain vaying amount of cabonate mineals and if these amounts inceased it will affect in some of soil popeties and make envionmental changes in which eflected on the gowth and the poduction of plant (Kishchuk, 2000). Iaqi soil content a high pecentage of cabonate mineals which anges between 15 35%, and it could be found less then 4% o moe than 60% depending on pevalent envionmental cicumstances and soil foming conditions. Calcite mineal constitutes the geate potion of cabonate mineals existing in the Iaqi soil which eaches the amount of 90% while the othe amount consists of Dolomite and Calcite holding magnesium (Al- Kaysi, 1983). Cabonate mineals in soil could be pimay inheited fom the mothe mateial o seconday accumulated by the opeations of soil foming (Al - Samaaie, 1975). So cabonate mineals found as a cove shape which cove the paticles and the accumulations of soil o accumulate in cacks, like flakes o accumulated gains in knots o veins (Gile, 196 1).The pesence of cabonate mineals in vaious potions affect in soil wate popeties such as the ability to hold wate, total poosity and poes size distibution (Singh et al., 2008). The esults of some eseaches (Al -Kubaisi, 1986; Khattab and Aljoboui, 2012; Muhmed and Wanatowski, 2013) have shown a diffeent effect of cabonate mineals in the ability of soil to hold wate sometimes inceases and sometimes deceases which means that the poous system of soil have been affected by cabonate mineals content and that leads to a combination of easons one of them is that the sedimentation of cabonate mineals in the intenal voids and capillay poes endings causing clogging so wate movement is obstucted and aise the pobability of keeping it o it is lining the capillay and non-capillay tubes causing decease in coss section aea and volume leading to decease the moistue content, o it coves the suface aea of clay paticles which decease the suface aea that holds wate cabonate mineals wok to fom soil maco aggegate which have a wide poe space that have low ability of keeping wate when exposed to wate tension. Poe space efes to the volume of soil voids that can be filled by wate and, o ai. It is effect and affected by the soil physical, chemical and biological popeties. All opeations and eactions occu though poe space such as the movement of wate and ai, dilution and sedimentation. In addition, poe space well known as a esidential place fo plant oots and soil oganisms (Abdollahi et al., 2014; Malik et al., 2015). The soil poe space chaacteized in to two featues poosity and poe size distibution. The poe size distibution consideed the most impotant featue fo it s complicated and stong elation with othe soil chaacteize especially with soil stuctue, stability of aggegates and paticle size distibution (Nimmo, 2004). Eynad et al. (2004) have found the impotance of soil poe size distibution fo it s affection on contolling fluid movement and stoage in soil which povides a space within the void occupied by ai 248

2 Impact of cabonate mineals content on soil poe size that is impotant fo the biological and physiological activity in hizosphee zone. Poe space is affected by many factos and the most impotant of them ae the way of packing, layeing and soil paticle distibution. Howeve poe space is always continuous change because of the affect of outside and inside stesses of the soil (McNabb et al., 2001). The poe space can be divided in to two volumetic goups in ode to study the poes size distibution. Macopoes defined as the ai poes and the micopoes which known as capillay poes. The activities ae affected by poes size distibution in which the capillay foces dominate such as cohesion, adhesion and the capability of wate etention in micopoes to become a souce poviding wate and dissolved mateials, while macopoes was impotant to ventilate the soil (Eynad et al., 2004; Nimmo, 2004). Goncalvesa et al. (2010) have mentioned thee volumetic categoies of poe space depending on active poosity concept: (i) cyptopoes which ae emaining poes less than 0.2 μm in diamete. (ii) micopoes which have volume anges between μm, and the capillay foces dominate in it. (iii) macopoes which was volume lage than 50 μm, and wate moves easily though it. Malik and Sheng-Gao (2015) have put five volumetic anges of poe space to classify soil poes size distibution. The elation between soil moistue content (θ) and wate tension (ψ) is non linea elati onship which is known as wate etention cuve and it is impotant to undestand the soil wate popeties (Hillel, 2004). Wate etention cuve is stongly elated with soil poes size distibution which was consideed a taditional way to evaluation and measuing poes size distibution (Stingaciu et al., 2010). Nimmo (2004) had eviewed modalities of measuing the sizes of soil poes and showed that the most used method was wate etention cuves which explains the behavio and liquid content of unsatuated poous media by adopting the idea of effective capillay size which gain o lose a cetain volume of liquid fom poes by the dying cuve o wetting cuve that showed by a diagam between θ and ψ whee the volumetic moistue content is a function of wate tension [θ (ψ)]. The objective of this eseach was to evaluate the soil poes system which had diffeent content of cabonate mineals by the function of poes size distibution. MATERIALS & METHODS An amount of loamy textue of soil mateial have taken fom a egion located in southen pat of Baghdad (longitude ' 34 " E, latitude ' 78 " N, altitude 33 m above sea level), Iaq. The soil mateial has died by ai in the laboatoy, cushed and sieved though a 2 mm sceen. Some of physical and chemical popeties have been estimated fo the soil mateial befoe the expeiment pocedue and table 1 shown the analysis esults. A soil mateial with 334 gm kg -1 content of cabonate mineals have been used to pepae new seven soil mateial with content of 305, 251, 203, 152, 103, 51, and 3.2 gm of cabonate mineals kg -1 soil, by emoving the cabonates using Sodium acetate (ph=5) accoding to the method that suggested by Holfod and Mattingly (1975). Anothe sample of soil has pepaed with a content of cabonate mineals geate than the highest level of cabonate in soil mateial and the method that suggested by Al-Ani and Dudas (1988) was used to pepae this sample. The cabonate content in this was about 352 gm cabonate mineals kg -1 soil. TABLE 1. Soil physical, chemical and hydaulic popeties Paamete Sand (gm kg -1 ) Silt (gm kg -1 ) Clay (gm kg -1 ) Textue Loam Bulk Density (Mg m -3 ) 1.52 Satuated hydaulic conductivity (cm h -1 ) 2.56 Volumetic wate content at 33 Kps (cm 3 cm -3 ) 0.23 Volumetic wate content at 1500 Kps (cm 3 cm -3 ) 0.08 Available wate (cm 3 cm -3 ) 0.15 Electical Conductivity (dsm -1 ) 1.33 Ph 7.58 CEC (Cmol c kg -1 soil) cabonate mineals (gm kg -1 ) * Popeties wee estimated accoding to methods descibed in [Klute, 1986; Page et al., 1982]. The elation estimated between volumetic wate content θ and wate tension ψ fo the pepaed soil samples. A Tempe cells have been used with a specification soil moistue equipment goup (Tempe cell No. 1400B0.5M2-3) to measue the moistue content at tensions fom zeo to -100 Kps, and a pessue plate appaatus fo tension of to Kps. The soil wate functions wee descibed using the van Genuchten equations (van Genuchten, 1980). Equation 1 was used to descibe the elation between θ and ψ. ( )[1 ( ) n ] m s (1) Whee θ is volumetic wate content at any value of ψ (cm 3 cm -3 ), θ is esidual wate content (cm 3 cm -3 ), θ s is satuated volumetic wate content (cm 3 cm -3 ), ψ wate tension Kps, and α, n, and m paamete elated with tension and the slope of moistue etention cuve which depends on poes size distibution. To evaluate the active poes sizes the equation of capillay ise used Young- Laplace equation eq. 2 (Stingaciu et al., 2010). 4 cos D= g Whee D is effective poe diamete (cm) and it s a function of poe volume, σ is a suface tension of wate (72.7 gm sec -2 at 20 C), β is contact angle between soil poe wall and wate, l w wate density (1 gm cm -3 ), and g is gavitational acceleation (980 cm sec -2 ). When substituting the values above in eq. 2, eq. 3 poduced to evaluate effective poe diamete D (3) (2) 249

3 I.J.S.N., VOL.9 (2) 2018: ISSN The void atio (e) calculated by: Vv e (dim ensionless) (4) Vs Whee V v is void volume (cm 3 ), V s is solid pat volume of soil (cm 3 ). Wate volume atio ν w also calculated in each soil sample when exposed to diffeent wate tensions fom zeo to Kps by applying eq. 5 that mentioned in Hillel (2004): Vw v w Vs Whee V w is wate volume (cm 3 ). RESULTS & DISCUSSION The moistue etention cuves of soil samples that have seveal contents of cabonate mineals as shown in (fig. 1). Thee wee diffeences between the cuves of the moistue etention fo diffeent soil teatments. The ability of soil samples to keep wate decease by the inceasing of cabonate mineals at evey wate tension level (fom -0.1 to Kps). Impotant changes happened to etained wate volume at diffeent tensions especially at deceased wate tensions in which the amount of etained wate deceased with the inceasing of cabonate mineals. And the volumetic moistue content θ was cm 3 cm -3 at wate tension 0.1 Kps of soil sample 3.2 gm kg -1 cabonate mineals content. The moistue content deceased continually and eached cm 3 cm -3 of soil sample 352 gm kg -1 cabonate mineals content with deceasing pecentage 21%. The volumetic moistue content has changed at 10 Kps with the change of cabonate mineals which eached 65, , , , , , 84, , and cm 3 cm -3 fo soil samples contents cabonate mineals 3.2, 51, 103, 152, 203, 251, 305, 334, and 325 gm kg -1 espectively. It s clea fom Fig.1 that the moistue content at 1500 Kps got the same behavio which the esidual wate content θ deceased with the inceasing of cabonate mineals fom to cm 3 cm -3 of soil sample content fom 3.2 to 352 gm kg -1 cabonate mineals with deceasing pecentage of wate content by 55%. The occued changes in volume of etained wate at diffeent wate tensions due to the change in total poosity of soil sample and the change in the poes size distibution due to the change of cabonate mineals. The effective diamete (eq.3) at wate tension 10 Kps shows that poe size lage than 30 μm, which losing wate content and the diffeence wate content between 0.1 and 10 Kps epesents noncapillay poes and it s also known as ai-filled poosity (ai poosity). While the diffeence of wate content between 10 and 1500 Kps epesents the wate holding capacity which equal the amount of wate and it s capillay poes filled with wate and it s volume less than 30 μm (Abdollahi et al., 2014; Eynad et al., 2004; Statsev and McNabb, 2001). (5) 250 wate content (θ) cm 3 cm -3 wate content (θ) cm3 cm-3 wate content (θ) cm 3 cm gm/kg gm/kg gm/kg wate tension (ψ) Kps FIGURE 1. Wate etention cuves of soil samples with vaious cabonate mineals content. Fig. 2 shows the volume of ai poes and the volume poes filled with wate at 10 Kps fo soil samples. The noncapillay poes filled with ai inceased with inceasing of cabonate mineals content, fo example the soil sample content 352 gm kg -1 cabonate mineals has the highest amount of poes filled with ai while the sample content 3.2 gm kg -1 cabonate mineals has the lowest amount of poes filled with ai. The atio of ai poes volume to the total volume of soil is 0.074, 0.080, 0.081, 0.084, 0.097, 0,097, 4, 4 and 5 cm 3 cm -3 fo samples content 3.2, 51, 103, 152, 203, 251, 305, 334, and 352 gm kg -1 cabonate mineals espectively. The capillay poes filled with wate (< 30 μm) was highest fo soil sample content 3.2 gm kg -1 cabonate mineals which eached cm 3 cm -3 and deceased to cm 3 cm -3 in the

4 Impact of cabonate mineals content on soil poe size sample content 352 gm kg -1 cabonate mineals, which means that the ability of soil to lose wate inceased with inceasing cabonate mineals. poes volume / total soil volume ai wate cabonate mineals content gm kg -1 FIGURE 2. Ai and wate distibution in soil sample content vaious cabonate mineals, Ai-filled poe volume (poes >30 μm diam.) and wate-filled poe volume (poes < 30 μm diam.). Fig. 3 shows the elationship between effective poes diamete (D) which calculated using eq. 3 and wate content (θ) fo soil samples with a vaious content of cabonate mineals. The inceasing effective poes diamete accompanied with incease wate content with decease cabonate mineals in soil sample. Fig. 3 epesents soil poes size distibution and it looks that the poe volume incease when the poe diamete decease, the poe volume can be estimated by the amount of wate content that kept in soil when exposed to cetain wate tension, and that epesents the diamete of soil poes which ae less than 30 μm confonting 10 Kps (fig.2), the atio wate content ( ), whee 0 < Θ <1 at 10 s Kps 10 each to the 0.786, 0.769, 0.764, 0.752, 0.716, 0.717, 0.696, 0.689, and fo soil samples content 3.2, 51, 103, 152, 203, 251, 305, 334, and 352 gm kg -1 cabonate mineals espectively. While the effective poes diamete that geate than 30 μm ae 0.213, 0.230, 0.236, 0.248, 0.284, 0.283, 4, 0.310, and which equals ( 1 ) fo soil samples espectively. It s clea s that the ai filled poes system type is mesopoes which is pemeable poes (Statsev and McNabb, 2001) which lost wate when soil sample exposed to tension of 10 Kps. the poes popotions in the poe space of soil samples anged between 21.4 and 33.0 %, while wate stoing poes which ae the poes that keep wate when exposed to tension of 10 Kps thei popotions anged between 67.0 and 78.6 %. This soil poes size distibution is consideed impotant to detemine the wate envionment of soil in which the soil sample have got a good popotion of pemeable poes and it s impotant to make wate move in soil fo that eason the soil samples that have modeate o high content of cabonate mineals (203, 251, 305, 334, and 352 gm kg -1 ) have good wate conductivity and diffusivity because of the incease in poes that convey wate which nealy eached as a atio quate poes system volume of soil sample. One of the soil poes size distibution evidence is void atio (eq.4) and it shows the change occued in each poes volume and solid soil mateial volume with in soil bulk volume. The void atio have been effected by cabonate mineals content with a value of 0.93 of 3.2 gm kg -1 cabonate mineals then the void atio of othe soil samples deceased and eached the value of 0.61 in the soil sample 352 gm kg -1 cabonate mineals with a deceasing pecentage of 34% (fig. 4). The change that occued in poes size distibution (fig. 2 and fig. 3) and void atio (fig. 4) caused a change in the amount of wate in soil sample when the content of cabonate mineals changes. wate content (θ) cm 3 cm -3 FIGURE 3. Relationship between effective poes diamete D and wate content θ fo soil sample content vaious cabonate mineals. Fig. 5 shows the elation between effective poes diamete and wate volume atio. It seems that amount of wate volume atio was little with in the micopoes, the wate volume atio inceases by the inceasing of effective poe size fo all soil samples that have a diffeent content of cabonate mineals. In the same time the amount of wate volume atio deceased by the inceasing of cabonate mineals content fo all effective soil poe diametes. void atio (e) g/kg 51 g/kg 103 g/kg 152 g/kg 203 g/kg 251 g/kg 305 g/kg 334 g/kg 352 g/kg Effective poes diamete (D) μm cabonate mineals content (gm kg-1) FIGURE 4. Void atio e (dimensionless) fo soil sample with vaious cabonate mineals content. 251

5 I.J.S.N., VOL.9 (2) 2018: ISSN wate volume atio (vw) g/kg 51 g/kg 103 g/kg 152 g/kg 203 g/kg 251 g/kg 305 g/kg 334 g/kg 80 FIGURE 5. Relationship between effective poes diamete D and wate volume atio ν w fo soil sample content vaious cabonate mineals. CONCLUSION It s concluded that the poes system of soil samples have effected by cabonate mineals content so that an incease occued in ai poes (geate than 30 μm ) with the inceasing of cabonate mineals content while the wate filled poes (less than 30 μm) deceased. When soil samples exposed to tension about 10 Kps. they lost moe amount of wate by the incease of cabonate mineals, in the sample of 352 gm kg -1 cabonate mineals lost moe wate with popotion of 22% compaed with the sample of 3.2 gm kg -1 cabonate mineals. ACKNOWLEDGEMENTS The fist autho wishes to expess his appeciation to D. Mahmoud K. Ahmed fo his comments and to M. Zaid N.T. fo tacing the figues and his help with this pape. REFERENCES Abdollahi, L., Munkholm, L.J. and Gabout, A. (2014) Tillage system and cove cop effects on soil quality: II. Poe chaacteistics. Soil Sci. Soc. Am. J. 78: Al-Ani, A.N. and Dudas, M. (1988) Influence of calcium cabonate on mean weight diamete of soils. Soil and Tillage Res. 11: Al-Kaysi, S.C.(1983) Physical and Chemical Chaacteization of Cabonate Mineals in Iaqi Soils. Ph.D. Dissetation, Dept. of Soil Sci. Newcastle upon Tyne, U.N. Al-Kubaisi, N.H. (1986) Effect of Calcium Cabonate on Some Physical and Minealogical Popeties of Soil. M. Sc. Thesis, Dept. of Soil Sci. College of Agicultue. Univesity of Baghdad. Iaq. p91. Al-Samaaie, M.Y. Gh. (1975) Micopedolo- gical Study of Highly Calcaeous Soil with Paticula Refeence to Iaq. Ph. D. Dissetation. Unive. of Reading, England. Bady, N.C. and Weil, B.R. (2014) The Natue and Popeties of Soils, 3 d Edition Soil Wate: Chaacteistics and Behavio. Peason Education Limited. pp Effective poes diamete (D) m 0 Chan, T.P. (2005) Modeling of Coase Textued Soils and Thei Hydaulic Popeties. Ph. D. Dissetation. Pudue Unevesity. p.177. Eynad, A., Schumache, T. E., Lindstom M. J. and Malo, D.D. (2004) Poosity and poe-size distibution in cultivated Ustolls and Ustets. Soil Sci. Soc. Am. J. 68: Gile, L.H. (1961) A classification of Ca -hoizon of deset egion, New Mexico. Soil Sci. Soc. Am. Poc. 30: Goncalvesa, R.A.B., Gloaguen, T.V., Folegatti, M.V., Libadi, P.L., Lucas, Y. and Montes, C.R. (2010) Poe size distibution in soils iigated with sodic wate and wastewate. R. Bas. Ci. Solo. 34: Hillel, D. (2004) Intoduction to Envionmental Soil Physics. Elsevie Academic Pess, Amstedam. 494 pp. Holfod, I.C.R. and Mattingly, G.E.G. (1975) Suface aeas of calcium cabonate in soils. Geodema. 13: Hong, S. Y., Minasny, B., Hwa Han, K., Kim, Y. and Lee. K. (2013) Pedicting and Mapping Soil Available Wate Capacity in Koea. National Academy of Agicultual Science, Rual Development Administation (RDA), Suwon, Gyeonggi-do, Republic of Koea. Khattab, S.I. and Aljoboui, M.M. (2012) Effect of combined stabilization by lime and cement on hydaulic popeties of clayey soil selected fom Mosul aea. Al-Rafadain Engineeing J. 20(6): Kishchuk, B.E. (2000) Calcaeous soils, thei popeties and potential limitations to conife gowth in southeasten Bitish Columbia and westen Albeta: a liteatue eview NOR-X-370. Klinkenbeg, L.J. (2009) Poe size distibu -tion of poous media and displacement expeiments with miscible liquids. J. Petoleum Tech. 9(4): Klute., A. (eds.) (1986) Methods of Soil Analysis: Pat 1 - Physical and Minealogical Methods. ASA and SSSA. SSSA Book Seies No. 5. Madison, WI: Soil Sci. Soc. Am. p Malik, Z. and Sheng-Gao, Lu. (2015) Poe size distibution of clayey soils and its coelation with soil oganic matte. Pedosphee. 25(2): McNabb, D.H., Statsev, A.D. and Nguyen, H. (2001) Soil wetness and taffic level effect on bulk density and ai-filled poosity of compacted boeal foest soils. Soil Sci. Soc. Am. J. 65: Muhmed, A. and Wanatowski, D. (2013) Effect of lime on the stength and micostuctue of clay. J. Mech. and Civil Eng. 6(3): Nimmo, J.R. (2004) Poosity and poe size distibution. In Hillel, D. (ed.) Encyclopedia of Soils in the Envionment: London, Elsevie. 3: Page, A. L., Mille, R. H. and Kenney, D. R. (1982) Methods of Soil Analysis.Pat 2. Chemical and 252

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