Soil Water Retention Curve and Specific Water Capacity for Three Different-Textured Soils

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1 IOSR Jounal of Agicultue and Veteinay Science (IOSR-JAVS) e-issn: , p-issn: Volume 11, Issue 9 Ve. II (Septembe 2018), PP Soil Wate Retention Cuve and Specific Wate Capacity fo Thee Diffeent-Textued Soils Namee T. Mahdi 1 1 (Dept. of Desetification Combat, College of Agicultue-Univesity of Baghdad, Iaq) Coesponding Autho: Namee T. Mahdi Abstact: A laboatoy expeiment was caied out to study some hydaulic popeties such as soil wate etention cuve (SWRC), poe size distibution (PSD), and specific wate capacity (SWC), fo thee diffeenttextued soils (sandy loam (SL), (SiL), and (SiCL)). The SWRC was estimated, and the equation of van Genuchten was used to detemine the best-fit paamete α, n, and m fo expeimental data of wate content- pessue head [θ(h)] which have nonlinea elationship. This study includes an expeimental investigation of the effect of soil paticles on PSD. The change in wate content θ of soil pe unit change in pessue head h was used to estimate SWC. The capillay ise equation (Juin equation) was used to estimate the effective poe diamete (D). The esults show that poe space was affected by expeimental soil samples. Ai poes (>30 μm) inceased with inceasing sand content at the same time capillay poes filled with wate (<30 μm) inceased with inceasing clay content. The elative of wate volume to total soil volume anged between 0.41 and 0.79 cm 3 cm -3 fo soil samples. At pessue head 100 cm the amount of wate lost inceased with sand content, whee soil sample SL lost wate moe than SiCL by 54%. The pecentage of poes (<30 μm) anged fom 41% to 79% and the poes (>30 μm) anged fom 59% to 21%. The paametes of van Genuchten equation consideed vey impotant to calculating the SWC fom the diffeential elation, and the amount of etained o lost wate has been estimated at vaious wate potential. Key wods: capillay ise equation, poe size distibution, diffeential wate capacity, poe diamete, van Genuchten equation Date of Submission: Date of acceptance: I. Intoduction Soil textue effects on hydo physical popeties of soil, and make envionmental changes in which eflected on the gowth and the poduction of plant [1]. The pesence of clay affect in soil wate popeties such as the ability to hold wate, total poosity and poes size distibution [2]. The effect of soil stuctue and textue is consideed by changing hydaulic conductivity, wate etention, oot gowth and tansfomation of the chemicals [3]. Howeve the poous system of soil have been effect by paticle size distibution, the shape of paticles, cementing, and packing density [4]. Poe space was the soil voids that can be filled by wate and, o ai, it is effect by the soil textue. All opeations and eactions occu though poe space such as the movement of wate and ai, dilution and sedimentation [5, 6]. 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 textue [7, 8]. The poe size distibution contolling fluid movement and stoage in soil and povides a space within the void occupied by ai that is impotant fo activity in hizosphee zone[9]. The Poe size distibution 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 effect of outside and inside stesses of the soil [10]. The poe space can be divided in to two volumetic goups. 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 [4, 9]. Ame, [11] used capillay ise equation to detemined poe size, the equivalent pessue anges of 0-10, 10-33, , , and > 1500 Kps, ae oughly coesponding to apidly daining poes, slowly daining poes, coase capillay poes, wate holding poes, and fine capillay poes diametes. Classes can be combined into total daining poes (0-33 Kps), and total wate stoage poes (>33 Kps),as well as into macopoes (<10 Kps) and soil matix poes (>10 Kps). Goncalvesa et al. [12] mentioned thee volumetic categoies of poe space depending on active poosity concept: cyptopoes (<0.2 μm in diamete), micopoes ( μm capillay foces dominate in it), and macopoes (>50 μm wate moves easily though it). DOI: / Page

2 Soil Wate Retention Cuve and Specific Wate Capacity fo Thee Diffeent-Textued Soils The wate content in an unsatuated soil is a function of the suction pesent in the soil, the elation between soil wate content (θ)-pessue head (h), [θ(h)] is nonlinea elationship which is known soil wate etention cuve (SWRC) and it is impotant to undestand the soil wate popeties [13]. Fom the SWRC a few paametes can be defined: the satuated volumetic wate content, the esidual volumetic wate content, the aienty value o bubbling pessue, and the esidual ai content [14]. A numbe of equations have been suggested fo the SWRC and almost all the equations wee suggested based on the shape of the SWRC, the geneal shape of the SWRC is nonlinea (sigmoid cuve), which have empiical paamete. The equation that povide a sigmoid cuve ae the equations of van Genuchten [15], and Fedlund and Xing [16], [17]. The SWRC was used fo detemining the soil hydaulic popeties such as unsatuated hydaulic conductivity, soil wate diffusivity, poosity and poe size distibution, and specific (o diffeential) wate capacity, both SWRC and unsatuated hydaulic conductivity ae often necessay fo solving unsatuated flow poblems [18, 19]. The SWRC is stongly elated with soil poes size distibution which was consideed a taditional way to evaluation and measuing poes size distibution [20]. Nimmo [4] 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 h whee the volumetic moistue content is a function of pessue head [θ(h)]. The objective of this eseach was to evaluate the soil poes system fo soil samples which had diffeent textue by the function of poes size distibution. II. Mateials And Methods Thee diffeent-textue soil samples, sandy loam (SL), silty loam (SiL), and (SiCL) wee used in this expeiment. All sample of distubed soil wee taken fom the A p hoizon (0-30 cm) of epesentative sites of the fields a egion located in west 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. Table 1. Physical, chemical and hydaulic popeties of the soil Paamete Soil sample Sandy loam Silt clay loam Sand (g kg -1 ) Silt (g kg -1 ) Clay (g kg -1 ) Bulk Density (Mg m -3 ) Volumetic wate content at 33 Kps (cm 3 cm -3 ) Volumetic wate content at 1500 Kps (cm 3 cm -3 ) Available wate (cm 3 cm -3 ) Satuated hydaulic conductivity (cm day -1 ) Electical Conductivity (dsm -1 ) ph CEC (Cmol c kg -1 soil) * Popeties wee estimated accoding to methods descibed in [21, 22]. The elation estimated between volumetic wate content θ and pessue head h fo the 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 wate potentials between -1 to-100 Kps, and a pessue plate appaatus in the ange -250 to Kps. The soil wate functions wee descibed using the van Genuchten equations [15]. Equation 1 was used to descibe the elation between θ and h. ( )[1 ( h) n ] m s (1) Whee θ is volumetic wate content (cm 3 cm -3 ) at any value of h, θ s and θ ae the satuated and esidual volumetic wate content of soil, espectively (cm 3 cm -3 ), h pessue head (cm), and α (elated to the invese of the ai-enty value) and n (elated to the slope of moistue etention cuve which depends on poes size distibution), and m, ae the fitting paametes of van Genuchten s model. d The diffeential of eq.1 was used to find the slope of SWRC ( ), it is called diffeential wate capacity dh o specific wate capacity (SWC). The diffeential fomula of SWC is: n 1 d nm( )( ) s h (2) dh n m 1 [1 ( h ) ] DOI: / Page

3 volumetic wate content (cm 3 cm -3 ) Soil Wate Retention Cuve and Specific Wate Capacity fo Thee Diffeent-Textued Soils To evaluate the diamete (D) of poes sizes, can be calculated by the equation of Juin equation eq. 2 [20]. 4 cos D (3) w g Whee D is effective poe diamete (cm) and it s a function of poe volume, σ is a wate suface tension (at 20 C= 72.7 g s -2 ), cosβ= 1, (β is contact angle between soil poe wall and wate its 0 fo a wetted suface), ρ w wate density (at 20 C= g cm -3 ), and g is the acceleation due to gavity (980 cm s -2 ). When substituting the values above in eq. 2, eq. 3 poduced to evaluate effective poe diamete D (4) III. Results and discussion Fig. 1 shows the soil moistue etention cuves (SWRC) of soil samples that have diffeent textue sandy loam (SL), (SiL), and (SiCL), (Table 1). Thee wee diffeences between the cuves of the moistue etention fo diffeent soil sample. The ability of soil samples to etained wate incease by the inceasing of clay contents at diffeent pessue head level (fom zeo to cm). The amount of etained wate at lowe pessue head (10 cm) deceased with the inceasing sand, the volumetic wate content (θ) was 0.589, 0.496, and cm 3 cm -3 fo SiCL, SiL, and SL espectively. Wate content has changed at pessue head 100 cm fo soil samples which deceased to 0.468, 0.306, and cm 3 cm -3 fo soil samples espectively. The moistue content at pessue head cm got the same behavio which the esidual wate content θ deceased with the inceasing of sand fom to 0.138, and cm 3 cm -3 fo soil samples espectively. The solid line in the fig. 1 efe to the best fitting of data of pessue head (h) against θ accoding to van Genuchten equation (eq.1). Eq. 1 shows good fitting between the obseved data and fitted data, the detemination coefficient (R 2 ) value was moe than fo soil samples, and declines the esidual man squae of θ (RMSθ), it was less than (cm 3 cm -3 ) 2, table 2 shows eq. 1 paametes which ae θ s, θ, α, n, and m sandy loam pessue head (cm) Fig. 1. Soil wate etention cuves fo,, and sandy loam Table 2. the values of van Genuchten equation paametes (θ s, θ, α, n, and m) fo soil wate etention cuves of soil samples (SiCL, SiL, and SL), and the values of best fitting paametes (R 2, RMSθ) Soil samples θ s θ α cm 3 cm -3 cm 3 cm -3 cm -1 n m R 2 RMSθ (cm 3 cm -3 ) 2 Silt clay loam ** Silt loam ** Sandy loam ** ** significance at 0.01 The diffeence of wate content between pessue head zeo and 100 cm epesents soil ai-filled poosity which is poes having size moe than 30 μm as effective poes diamete (eq. 3), while the wate content diffeence between pessue head 100 and cm which is wate-filled poosity and thei size less than 30 μm and it is defined as wate holding capacity o available wate o field capacity [9, 14]. Fig 2 shows atio of poes volume which is filled by ai, wate and esidual wate content to bulk soil volume of diffeent textue soils. It is seemed that the volume atio of ai-filled poosity declines with incease clay content and the soil sample SiCL had lowest ai-filled poes atio (0.121 cm 3 cm -3 ), while the SL soil had the highest ai-filled poes atio (0.223 cm 3 cm -3 ), this means that the SL soil has an incease by 1.8 times of the ai-filled poes volume. The wate-filled poes atio was low in SL soil sample (0.059 cm 3 cm -3 ) and it inceased in the SiCL soil sample to be the highest wate-filled poes atio (0.272 cm 3 cm -3 ), and this means that soil ability to lose wate inceases with incease of sand content and this may attibuted to ability of these samples to elease moe wate quantity DOI: / Page

4 specific wate capacity (cm -1 ) poe volume / bulk soil volume Soil Wate Retention Cuve and Specific Wate Capacity fo Thee Diffeent-Textued Soils than the samples that have less sand content at the same wate potentials. This can be intepeted by using the slope of wate etention cuves (SWC). The esidual volumetic wate content (θ ) of soil samples inceased with inceasing of clay content, in this case the volume of etained wate depending on the specific suface aea of soil paticle and the clay had highest specific suface aea (table 2) Ai Wate Residual wate Sandy loam Fig. 2. Ai and wate distibution in thee soil sample, Ai-filled poe volume (poes >30 μm diam.) and wate-filled poe volume (poes < 30 μm diam., wate + esidual wate). d The elationship between absolute value of SWRC slope (, SWC) and pessue head fo thee dh expeimental soils ae shown in fig. 3. It can be noticed that the SWC inceases with pessue head incease till eaching the highest slope peak, and this was taken place at cm pessue head of soil samples. The maximum values of SWC was , , and fo SL, SiL, and SiCL espectively. The SiCL soil sample showed slight change in SWC values stating fom zeo to 50 cm pessue head, afte that the values of SWC deceased with inceasing pessue head and each the minimum values at pessue head cm. This decline included all soil samples. The change taken place in the absolute value of SWRC slope and the obtained change in peak of SWC was a esult of effect of soil textue on poes volume distibution and this shows pogessive cuvatue in cuve peaks with sand content incease. Fo this eason, the soil sample content high sand was moe ability to lose wate when it was subjected to applied pessue head. Fig. 4 shows the elationship between effective poe diamete (D) and SWC values, this elationship called poe size fequency distibution function. Fom the figue the poe size anged fom 0.2 to the μm accoding to the eq. 4 fo all soil samples. The peak of the elationship efe to the poe size at 100 μm, this poes size and moe lose wate at pessue head anged between cm, and the soil sample had the maximum values of SWC quickly lose wate fom poes size > 100 μm, so the expeimental soil samples lose wate accoding to the ode in follows SL > SiL > SiCL. 4.0E E E E-03 Sandy loam 2.0E E E E E pessue head (cm) Fig. 3. The elationship of SWC (cm -1 ) with pessue head (cm) fo,, and sandy loam DOI: / Page

5 α (cm -1 ) specific wate capacity (cm -1 ) Soil Wate Retention Cuve and Specific Wate Capacity fo Thee Diffeent-Textued Soils 4.0E E E E E E E E E+00 Sandy loam Effective poes diamete (μm) Fig. 4. The elationship of SWC (cm -1 ) with effective poes diamete (μm) fo,, and sandy loam One of the soil poes size distibution evidence is the elationship between α (cm -1 ), and the maximum absolute value of SWC (cm -1 ). Kind of this is shown in fig. 5 which indicated pesence linea positive elation between α and maximum value of SWC, the ageement was good as indicated the coelation coefficient (= 0.788). The incease of maximum value of SWC and value of α inceased in all of expeimental soil samples. As it is lastly known that incease of maximum value of SWC of wate etention cuves was coelated with incease of sand content, and α values also wee coelated with incease of thei values with sand content (Table 2). So the linea positive elation was obtained between α and maximum value of SWC, and this emphasized that the soil poous system and the poes size distibution wee affected by the pimay soil paticles content and, this was eflected on available wate and the amount of wate holding when soil was subjected to applied wate potential and the quantity of the hold wate is consideed as function of effective poes diamete at the applied wate potential maximum specific wate capacity (cm -1 ) Fig. 5. The elationship of maximum SWC (cm -1 ) with α (cm -1 ) fo,, and sandy loam The elation of effective poes diamete that estimated fom eq. 4 with the volumetic wate content fo expeimental soil samples was shown in fig. 6. It was noticed that incease of the effective poes diamete caused incease of soil wate content. When the effective poes diamete is less than 30 μm, the soil wate content inceases with decease of the sand content, and it may be due to that the wate content in these cicumstances is connected with the poe size distibution and with the specific suface aea. With incease of the effective poes diamete (fom 50 to 150 μm), the wate content inceased with clay content incease, the eason of that was due to soil poosity incease (Table 1). The epesents cuve of poe size distibution noticed that poe volume incease stongly with decease of poe diamete and it may be concluded on poe volume in soil samples fom soil wate quantity which is maintained by soil when specific wate potential is applied and this epesents soil poes having less than 30 μm in diamete. The atio of the poe volume that keeping wate when soil samples wee subjected to pessue head 100 cm was 0.41, 0.62, and 0.79 as the atio wate content ( ), whee 0 < Θ <1 fo soil samples contained clay 105, 204 and 367 g kg -1 espectively. The poe s volume atio that had active diamete moe than 30 μm anged between 0.59 to 0.21, and this was equals ( 1 ) fo soil samples espectively. The ai-filled poes system was as mesopoes kind which ae s wate tanspoting poes [14] and wate may be dained when soil exposed to pessue head 100 cm. while the DOI: / Page

6 volumetic wate content (cm 3 cm -3 ) Soil Wate Retention Cuve and Specific Wate Capacity fo Thee Diffeent-Textued Soils wate stoed poes which ae keeping wate when they ae exposed to pessue head 100 cm it is micopoes kind. This poes size distibution of soil poes is impotant to detemine the biological and aqueous soil envionment as soil samples had good atio of the tanspoting wate poes and it is impotant fo wate movement and diffusion in soil, so the samples with high sand content chaacteized by good wate diffusion and conductivity due to incease of the tanspoting wate poes which wee moe than half of the poous system volume of SL soil sample. The expeimental soil samples SiCL and SiL had little maco poes and it can be known fom the slope of SWRC till 100 cm pessue head was small slope due to flat state of the cuve at low wate potential, especially at satuated conditions Sandy loam Effective poes diamete (μm) Fig. 6. Relationship between effective poes diamete D and wate content θ fo,, and sandy loam IV. Conclusion The behavio of SWC mostly depends on paticle size distibution, total poosity, poe size distibution, and wate content. The maximum values of SWC incease with inceasing sand content. The poes system of the expeimental soil samples have effected by pimay soil paticles content so that the ability of soil samples to etained wate incease by the inceasing of clay contents at diffeent pessue head. The incease occued in ai poes (geate than 30 μm) with the inceasing of sand content while the wate filled poes (less than 30 μm) incease with clay inceased. When soil samples exposed to pessue head about 100 cm, the soil sample SL lost wate moe than SiCL by 50%. Refeences [1]. D. Hillel, Intoduction to Envionmental Soil Physics (Elsevie Academic Pess, Amstedam., 2004). [2]. N. J. Javis, A eview of non-equilibium wate flow and solute tanspot in soil macopoes: pinciples, contolling factos and consequences fo wate quality, Eu. J. Soil Sci., , [3]. J. Lipiec, J. Avidsson, and E. Mue, Review of modeling cop gowth, movement of wate and chemicals in elation to topsoil and subsoil compaction, Soil Till. Res.,73, 2003, [4]. J. R. Nimmo, Poosity and poe size distibution, in D. Hillel (Ed.) Encyclopedia of Soils in the Envionment, 3 (London, Elsevie, 2004) [5]. L. Abdollahi, L. J. Munkholm, and A. Gabout, Tillage system and cove cop effects on soil quality: II. Poe chaacteistics, Soil Sci. Soc. Am. J., 78, 2014, [6]. Z. Malik, and Lu. Sheng-Gao, Poe size distibution of clayey soils and its coelation with soil oganic matte, Pedosphee. 25(2), 2015, [7]. S. Assouline, Modeling the elationship between soil bulk density and the wate etention cuve, Vadose Zone J., 5, 2006a, [8]. S. Assouline, Modeling the elationship between soil bulk density and the hydaulic conductivity function, Vadose Zone J., 5, 2006b, [9]. A. Eynad, T. E. Schumache, M. J. Lindstom, and D. D. Malo, Poosity and poe-size distibution in cultivated Ustolls and Ustets, Soil Sci. Soc. Am. J. 68, 2004, [10]. D. H. McNabb, A. D. Statsev, and H. Nguyen, Soil wetness and taffic level effect on bulk density and ai-filled poosity of compacted boeal foest soils, Soil Sci. Soc. Am. J. 65, 2001, [11]. A. M. Ame, Wate flow and conductivity into capillay and non-capillay poes of soil, J. Soil Sci. Plant Nut., 12(1), 2012, [12]. R. A. B. Goncalvesa, T. V. Gloaguen, M. V. Folegatti, P. L. Libadi, Y. Lucas, and C. R. Montes, Poe size distibution in soils iigated with sodic wate and wastewate, R. Bas. Ci. Solo, 34, 2010, [13]. X. Wang, and C. H. Benson, Leak-fee pessue plate extacto fo measuing the soil wate chaacteistic cuve, Geo. Tes. J., 27(2), 2004, [14]. A. D. Statsev, and D. H. McNabb, Skidde taffic effects on wate etention, poe-size distibution, and van Genuchten paametes of boeal foest soils, Soil Sci. Soc. Am. J. 65, 2001, [15]. M.Th. van Genuchten, A closed-fom equation fo pedicting the hydaulic conductivity of unsatuated soils, Soil Sci. Soc. Am. J., 44, 1980, [16]. D. G. Fedlund, and A. Xing, Equations fo the soil-wate chaacteistic cuve, Can. Geotech. J., 31, 1994, [17]. E. C. Leong, and H. Rahanljo, Review of soil-wate chaacteistic cuve equations, Jounal of Geotechnical and Geoenvionmental Engineeing, 1997, [18]. T. P. Chan, Modeling of Coase Textued Soils and Thei Hydaulic Popeties, doctoal diss., Pudue Univesity, DOI: / Page

7 Soil Wate Retention Cuve and Specific Wate Capacity fo Thee Diffeent-Textued Soils [19]. J. Zhuang, K. Nakayama, G. R. Yu, T. Miyazaki, Pedicting unsatuated hydaulic conductivity of soil based on some basic soil popeties, Soil Tillage Reseach, 59, 2001, [20]. L. R. Stingaciu, L. Weihemulle, S. Habe- Pohlmeie, S. Stapf, H. Veeecken, and A. Pohlmeie, Detemination of poe size distibution and hydaulic popeties using nuclea magnetic esonance elaxomety: A compaative study of laboatoy methods. Wate Resou. Res., 46(11), 2010, 1-6. [21]. A. Klute, (eds.), Methods of soil analysis: pat 1-physical and minealogical methods (ASA and SSSA. SSSA Book Seies No. 5. Madison, WI: Soil Sci. Soc Am, 1986). [22]. A. L. Page, R. H. Mille, and D. R. Kenney, Methods of Soil Analysis. Pat 2. Chemical and biological popeties (USA. Ame. Soc. Agon. Inc. Publishe, Madison, Wisconsin, 1982). Namee T. Mahdi. " Soil Wate Retention Cuve and Specific Wate Capacity fo Thee Diffeent- Textued Soils." IOSR Jounal of Agicultue and Veteinay Science (IOSR-JAVS) 11.9 (2018): DOI: / Page