Effect of SOC in the form of amendments on hydraulic...

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INTERNATIONAL JOURNAL OF CIVIL AND STRUCTURAL ENGINEERING Volume 4, No 3, 2014 © Copyright by the authors - Licensee IPA- Under Creative Commons license 3.0 Research article ISSN 0976 – 4399 Received on March, 2014 Published on May 2014 450 Effect of SOC in the form of amendments on hydraulic properties of arid soils Guruprasad M. Hugar 1 Veena .S. Soraganvi 2 1 Dept. of Civil Engineering, Government Engineering College, Raichur-584134, Karnataka, India. 2 Dept. of Civil Engineering, Basaveshwar Engineering College, Bagalkot-587102, Karnataka, India. [email protected] doi: 10.6088/ijcser.201304010043 ABSTRACT Raichur district is located in the northern region of Karnataka; it is drought prone and falls in the arid tract of India. The climate here is dry for the major part of the year. The low and highly variable rainfall renders the district liable to drought. Increasing the soil waterholding capacity (WHC) has been a major concern in this area. Increasing soil organic carbon (SOC) is vital in terms of improving the soil properties related to conditions for crop development and tillage traffic in arid and semiarid regions. This study is conducted to characterize the threshold limit of SOC with respect to WHC and hydraulic conductivity (K) in four of the arid soils namely black cotton, red, marshy and mountainous soils. Wastes like humus, pressmud, bagasseash and flyash were used as a source of SOC to amend with the soils. SOC inputs were made volumetrically up to 70% in the increments of 10% of the soil columns; there was also a control column without any external addition of SOC. The relation between SOC, WHC and K was analyzed by series of experiments carried in triplicate in three different phases based on the mode of application of SOC. The highest WHC’s achieved were 92.8%, 78.9%, 88.3 and 76.3% similarly highest K were 6.5E-06 cm/s, 2.5E-05cm/s, 1.8E-05 cm/s and 2.6E-05cm/s for black cotton, red, marshy and mountainous soils respectively. Phase III performed better for all the soils with respect to WHC and K. The positive relation between threshold limits of SOC, WHC and K was obtained. Keywords: WHC, K, SOC, Threshold limit and mode of application. 1. Introduction The amount of SOC existing in a soil is the balance between organic carbon input and output. It is influenced by soil type, climate, management and the interactions between each of these. Any changes made to the natural status of the soil systems (conversion to agriculture, deforestation, plantation) will result in variation of SOC. Therefore, disturbed systems may still be in the process of attaining a new equilibrium C content and any measurements of SOC have to take into account that the soil is in the process of re-establishing equilibrium, which is more than 50 years (Baldock and Skjemstad, 1999). It is now widely recognized that SOC plays an important role in soil biological (provision of substrate and nutrients for microbes), chemical (buffering and pH) changes and physical (stabilization of soil structure) properties. The term “soil quality” has been refined and expanded by scientists and policy makers to include its importance as an environmental buffer, in protecting watersheds and groundwater from agricultural chemicals and municipal wastes and sequestering carbon that would otherwise contribute to a rise in greenhouse gases and global climate change, Reeves (1997). However, the general perception of a healthy or high-quality soil is one that adequately performs functions, which are important to humans, such as providing a medium for plant

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INTERNATIONAL JOURNAL OF CIVIL AND STRUCTURAL ENGINEERING Volume 4, No 3, 2014

© Copyright by the authors - Licensee IPA- Under Creative Commons license 3.0

Research article ISSN 0976 – 4399

Received on March, 2014 Published on May 2014 450

Effect of SOC in the form of amendments on hydraulic properties of arid soils

Guruprasad M. Hugar1 Veena .S. Soraganvi 2 1Dept. of Civil Engineering, Government Engineering College, Raichur-584134, Karnataka,

India. 2Dept. of Civil Engineering, Basaveshwar Engineering College, Bagalkot-587102, Karnataka,

India. [email protected]

doi: 10.6088/ijcser.201304010043 ABSTRACT Raichur district is located in the northern region of Karnataka; it is drought prone and falls in the arid tract of India. The climate here is dry for the major part of the year. The low and highly variable rainfall renders the district liable to drought. Increasing the soil water-­‐holding capacity (WHC) has been a major concern in this area. Increasing soil organic carbon (SOC) is vital in terms of improving the soil properties related to conditions for crop development and tillage traffic in arid and semiarid regions. This study is conducted to characterize the threshold limit of SOC with respect to WHC and hydraulic conductivity (K) in four of the arid soils namely black cotton, red, marshy and mountainous soils. Wastes like humus, pressmud, bagasseash and flyash were used as a source of SOC to amend with the soils. SOC inputs were made volumetrically up to 70% in the increments of 10% of the soil columns; there was also a control column without any external addition of SOC. The relation between SOC, WHC and K was analyzed by series of experiments carried in triplicate in three different phases based on the mode of application of SOC. The highest WHC’s achieved were 92.8%, 78.9%, 88.3 and 76.3% similarly highest K were 6.5E-06 cm/s, 2.5E-05cm/s, 1.8E-05 cm/s and 2.6E-05cm/s for black cotton, red, marshy and mountainous soils respectively. Phase III performed better for all the soils with respect to WHC and K. The positive relation between threshold limits of SOC, WHC and K was obtained.

Keywords: WHC, K, SOC, Threshold limit and mode of application.

1. Introduction

The amount of SOC existing in a soil is the balance between organic carbon input and output. It is influenced by soil type, climate, management and the interactions between each of these. Any changes made to the natural status of the soil systems (conversion to agriculture, deforestation, plantation) will result in variation of SOC. Therefore, disturbed systems may still be in the process of attaining a new equilibrium C content and any measurements of SOC have to take into account that the soil is in the process of re-establishing equilibrium, which is more than 50 years (Baldock and Skjemstad, 1999). It is now widely recognized that SOC plays an important role in soil biological (provision of substrate and nutrients for microbes), chemical (buffering and pH) changes and physical (stabilization of soil structure) properties. The term “soil quality” has been refined and expanded by scientists and policy makers to include its importance as an environmental buffer, in protecting watersheds and groundwater from agricultural chemicals and municipal wastes and sequestering carbon that would otherwise contribute to a rise in greenhouse gases and global climate change, Reeves (1997). However, the general perception of a healthy or high-quality soil is one that adequately performs functions, which are important to humans, such as providing a medium for plant

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Effect of SOC in the form of amendments on hydraulic properties of arid soils Guruprasad M. Hugar

International Journal of Civil and Structural Engineering

Volume 4 Issue 3 2014

451

growth and biological activity, regulating and partitioning water flow and storage in the environment and serving as an environmental buffer in the formation and destruction of environmentally hazardous compounds. Considering this wide variety of performance indicators Karlen et al. (2003) and Norfleet et al. (2003) pointed out that soil quality needs to be assessed with regard to what the soil is used for, as a particular, soil may be of high quality for one function and may perform poorly for another. Suitability of soil for sustaining plant growth and biological activity is a function of physical (porosity, water holding capacity, structure and tilth) and chemical properties (nutrient supply capability, pH, salt content), many of which are a function of soil organic carbon (SOC) content Doran and Safley (1997). Similarly Elliott (1997) indicated that SOC was a key indicator of soil health. In general, increases in SOM are seen as desirable by many farmers as higher levels are viewed as being directly related to better plant nutrition, ease of cultivation. Carter and Stewart (1996), Lal (1979) and Reeves (1997) noted that “SOC is the most often reported attribute from long-term agricultural studies and is chosen as the most important indicator of soil quality and agronomic sustainability because of its impact on other physical, chemical and biological indicators of soil quality”. However Jazen (1992) pointed out relationship between soil quality indicators (SOC) and soil functions does not always comply to a simple linear relationship and therefore “bigger is not necessarily better”. The amount of SOC accumulated in the soil per gm of organic material applied can vary greatly depending on the carbon content of the amendment and its degradability (Haynes and Naidu, 1998). The addition of organic amendments has been documented to increase soil water holding capacity (Konomi et al., 2005; Curtis and Claassen, 2005; FAO, 2001). Liquid retention in the porous soil matrix is highly dependent on the shape and angularity of individual pores. Natural pore spaces do not resemble cylindrical capillaries, as often assumed for an idealized representation. Since natural porous media are formed by aggregation of primary particles and mineral surfaces, the resulting pore space is more realistically described by angular or slit-shaped pore cross sections than by cylindrical capillaries (Li et al., 1986; Mason and. Morrow, 1991). In addition to a more realistic representation of natural pore spaces, angular pores offer other advantages over cylindrical tubes in terms of liquid behavior. When angular pores are drained, a fraction of the wetting phase remains in the pore corners. This aspect of “dual occupancy” of the invaded portion of the tube (Morrow and Xie, 1998), is not possible in cylindrical tubes, more realistically represents liquid configurations and mechanisms for maintaining hydraulic continuity in porous media (Dullien et al., 1986). Liquid-filled corners and crevices play an important role in displacement rates of oil (Singh et al., 2003) and in other transport processes in partially saturated porous media. The positive relationship exists between SOC, WHC and K which if quantified can be of immense importance for vegetation growth, infiltration, ground water recharge and other physical and hydraulic properties of soil. Further such studies have not been performed on Indian soil; therefore this study is carried on arid soils to explore the nexus of SOC with WHC and K. Raichur district is drought prone and falls in the arid tract of the country. The climate of the district is characterized by dryness for the major part of the year and a very hot summer with the average temperature of 400C. The low and highly variable rainfall renders the district liable to drought. The normal annual rainfall of the district is 621mm (GOI, booklet). The annual numbers of the rainy days are about 49. Industrial and agriculture sector are mutually dependent. Irrigation alone cannot cover the whole part of this zone hence it is the need of hour to effectively utilize the available rain water for cultivation as well to recharge the groundwater table.

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Effect of SOC in the form of amendments on hydraulic properties of arid soils Guruprasad M. Hugar

International Journal of Civil and Structural Engineering

Volume 4 Issue 3 2014

452

2. Materials and methods Study was conducted in Raichur a district head quarter located in the northern region of Karnataka state (16022’32.38”N 77021’38.50”E), which is drought prone and falls in the arid tract of the India. The climate of the district is characterized by dryness for the major part of the year and a very hot summer. 2.1 Soils used A preliminary survey was carried out in different locations in and around Raichur, to select the soil samples for the study. Four soils namely black cotton, marshy, red and mountainous soil were taken from different locations by removing the top 5cm soil with ten samples from each location. Such of the collected samples were analyzed for particle size, field density and SOC as depicted in Walkely and Black (1934) 2.2 Soil amendments

2.2.1 Flyash Ash produced during combustion of coal, combustion has certain amount of loss on ignition (LOI) value that speaks of the unburnt matter this will still retain its organic carbon content (Ram et al., 1999; Indrek et al., 2004).Class “F” category procured from Raichur thermal Power plant of Karnataka, called Raichur Fly ash (RFA) was used in the study as a source of SOC and an amendment. Composition of Fly ash is given in Table 1 2.3 Bagasseash Sugar cane Bagasse is an industrial solid waste obtained after having extracted the juice by crushing the sugar cane, it is used worldwide as fuel in the same sugar industry. The combustion yields ashes containing high amounts of unburnt matter, silicon and aluminum oxides as main components. Bagasse ash was obtained from the Core Green Sugar & fuels Pvt. Ltd. An Industry located in Yadgir, Karnataka, and composition of Bagasse ash is given in Table 1. 2.4 Humus It is the plant/animal residue that does not completely mineralize. A certain part of this residue is more or less resistant to microbial decomposition and remains for a period of time as an un-decomposed or in a somewhat modified state, and may even accumulate under certain conditions. Typical composition of humus is given in the Table 1 (Selman, 1986) 2.5 Pressmud Pressmud is a waste by-product from sugar factories. It is a soft, spongy, amorphous and dark brown to brownish material which contains sugar, fiber, coagulated colloids, including cane wax, albuminoids, inorganic salts and soil particles. By virtue of the composition and high content of organic carbon, the usefulness of pressmud as a valuable organic manure has been reported by several workers (Nehra and Hooda, 2002; Ramaswamy, 1999). Pressmud is a potential source of major minerals as well as trace elements that can substitute chemical

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Effect of SOC in the form of amendments on hydraulic properties of arid soils Guruprasad M. Hugar

International Journal of Civil and Structural Engineering

Volume 4 Issue 3 2014

453

fertilizers. Press mud was obtained from the above said sugar industry. Composition of Press mud is given in Table 1.

Table 1: Composition of amendments

Constituents Flyash Bagasse

ash Constituents Humus

Constituents Pressmud

% % % % (Except pH)

SiO2 61.10 78.34 Water soluble fraction 7 pH 4.95

Al2O3 28.00 08.55 Hemicelluloses 18.52 Total Solids 27.87

TiO2 1.30 1.07 Cellulose 11.44 Volatile Solids 84.00

Fe2O3 4.20 3.61 Lignin 47.64 C.O.D 117.60 MgO 0.80 - Protein 10.06 B.O.D 22.20

CaO 1.7 2.15 Ether-soluble fraction 5.34 OM 84.12

K2O 0.18 3.46 pH 5.6 N 1.75 Na2O 0.18 0.12 SOM 0.83 P 0.65 LOI 2.40 7.42 SOC 0.28 K 0.28

SOM 0.89 0.85 Na 0.18 SOC 0.3 0.29 Ca 2.7

SOM 0.71 SOC 0.24

3. Particle size analysis of soils and amendments Sieve analysis was performed for all the collected soil samples as per IS: 460-1962 and grouped accordingly in soil class. BC soil was clayey sand with high plasticity, having 38% sand and 62% silt & clay. Red soil was clayey sand with intermediate plasticity, having 41% sand and 59% silt & clay. Mountainous soil was silty sand with low plasticity, having 42% sand and 58% silt & clay and marshy soil was non Plastic, with 77% sand and 23% silt & clay. Similarly Bagasseash particles were uniform non-granular and average particle sizes ranged between 7 µm to 12 µm, Fly ash had 1% clay, 12% of silt and 87% of sand content. Pressmud was coarser than rest of the amendments with its particle size ranging from 0.1µ to 1mm (20%), 1mm to 10mm (80%). Humus had 38% of fine sand fraction, 35% silt sized fraction and 27% clay sized fraction. 3.1 Test procedure Soil columns with dimensions 10 cm diameter and 30 cm length were fabricated by acrylic tubes and were then packed with the collected soil samples to their respective densities. The study was carried out in three phases based on the mode of application of SOC to soil as explained below. 3.2 Phase I Soil-amendment combinations were individually assessed for their threshold SOC limits based on obtained highest WHC by replacing 0 to 40% volumes of soil with waste (SOC) and

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Effect of SOC in the form of amendments on hydraulic properties of arid soils Guruprasad M. Hugar

International Journal of Civil and Structural Engineering

Volume 4 Issue 3 2014

454

blending it with the top 15cm soil of the column, which resulted in 0.09 -0.55gm/gm with humus, 0.1-0.62 gm/gm with bagasseash, 0.2-1.19 gm/gm with pressmud and 0.08-0.5 gm/gm with flyash for BC soil. For red soil it was 0.07 -0.39gm/gm with humus, 0.07-0.45 gm/gm with bagasseash, 0.14-0.86 gm/gm with pressmud and 0.06-0.36 gm/gm with flyash. For marshy soil it was 0.07 -0.41gm/gm with humus, 0.08-0.47 gm/gm with bagasseash, 0.15-0.9 gm/gm with pressmud and 0.06-0.38 gm/gm with flyash. For mountainous soil it was 0.08 gm/gm -0.47gm/gm with humus, 0.09-0.53 gm/gm with bagasseash, 0.17-1.02 gm/gm with pressmud and 0.07-0.42 gm/gm with flyash. 3.3 Phase II Soil-amendment combinations were individually assessed for their threshold SOC limits by replacing 0 to 70% volumes of soil with waste (SOC) and blending it with the complete soil of the column, which resulted in 0.09 -1.92gm/gm with humus, 0.1-2.18 gm/gm with bagasseash, 0.2- 4.18 gm/gm with pressmud and 0.08-1.74 gm/gm with flyash for BC soil. For red soil it was 0.07 -1.37gm/gm with humus, 0.07-1.56 gm/gm with bagasseash, 0.14-2.99 gm/gm with pressmud and 0.06-1.25 gm/gm with flyash. For marshy soil it was 0.07 -1.45gm/gm with humus, 0.08-1.65 gm/gm with bagasseash, 0.15-3.16 gm/gm with pressmud and 0.06-1.32gm/gm with flyash. For mountainous soil it was 0.08 gm/gm -1.63gm/gm with humus, 0.09-1.86 gm/gm with bagasseash, 0.17-3.57 gm/gm with pressmud and 0.07-1.49 gm/gm with flyash. 3.4 Phase III This phase was similar to phase II with the only difference that amendments were just stacked at top without blending with soil. 4. Water holding capacity determination The soil columns were amended as briefed in the above phases. Three sets of soil columns for each soil-amendment combination were prepared , saturated and kept overnight. To such of the columns water was pounded and was then allowed to drain, the drained volumes were recorded. The process was repeated till the steady drained volumes were obtained. The soil columns were subjected for 24 hours of drain and then water holding capacity (WHC) was determined by the triplicate columns by oven drying the sample from the column as per IS: 2720 (Part II)-1969. The SOC input for a soil that held the highest water was recorded as its threshold SOC limit. 4.1 Hydraulic conductivity Hydraulic Conductivity of the control and amended soil combinations were tested by Falling head permeability as per IS: 2720 (Part XVII). Each soil amendment combinations were placed in moulds by compacting them to their field density, with triplicates. Samples were saturated and kept overnight before starting the conductivity test. 4.2 Results and discussion BC soil was clayey, mountainous soil was sandy silt, marshy and red soil were sandy clay. Except marshy soil rest of the soil particles in their micro structure are angular both at surface and at edges. While marshy soil resembled the sphere or a cylinder in its microstructure.

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Effect of SOC in the form of amendments on hydraulic properties of arid soils Guruprasad M. Hugar

International Journal of Civil and Structural Engineering

Volume 4 Issue 3 2014

455

Similarly all the amendments except flyash in their microstructure are angular or nearly angular in their shape, while flyash is perfectly spherical in its shape. Pressmud had its surface spherical in microstructure. Experiments were conducted with disturbed soil samples to study the response of SOC on WHC & K of arid soils. All the amendments improved WHC when compared with the control. Studies like (Bauer, 1981; Rawls et al., 2003) found that the effect of organic carbon on water retention in disturbed samples was substantial in sandy soil and marginal in medium- and fine textured soils. In the present study SOC improved both WHC & K of all the soils irrespective of the soil type.

Figure 1a : SOC Vs WHC on BC soil @ phase I

Figure 1b: SOC Vs K on BC soil @ phase I

Figure 1c: SOC Vs WHC on BC soil @ phase II

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Effect of SOC in the form of amendments on hydraulic properties of arid soils Guruprasad M. Hugar

International Journal of Civil and Structural Engineering

Volume 4 Issue 3 2014

456

Figure 1d: SOC Vs K on BC soil @ phase II

Figure 1e:SOC Vs WHC on BC soil@ phase III

Figure 1f: SOC Vs K on BC soil@ phase III

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Effect of SOC in the form of amendments on hydraulic properties of arid soils Guruprasad M. Hugar

International Journal of Civil and Structural Engineering

Volume 4 Issue 3 2014

457

Figure 2a: SOC Vs WHC on Red soil @ phase I

Figure 2b: SOC Vs K on Red soil @ phase I

Figure 2c: SOC Vs WHC on Red soil @ phase II

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Effect of SOC in the form of amendments on hydraulic properties of arid soils Guruprasad M. Hugar

International Journal of Civil and Structural Engineering

Volume 4 Issue 3 2014

458

 

Figure 2d: SOC Vs K on Red soil @ phase II

Figure2e: SOC Vs WHC on Red soil @phase III

Figure 2f: SOC Vs K on Red soil @ phase III

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Effect of SOC in the form of amendments on hydraulic properties of arid soils Guruprasad M. Hugar

International Journal of Civil and Structural Engineering

Volume 4 Issue 3 2014

459

Figure 3a: SOC Vs WHC on Marshy soil @ phase I

 

Figure 3b: SOC Vs K on Marshy soil @ phase I

Figure 3c: SOC Vs WHC on Marshy soil @ phase II

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Effect of SOC in the form of amendments on hydraulic properties of arid soils Guruprasad M. Hugar

International Journal of Civil and Structural Engineering

Volume 4 Issue 3 2014

460

Figure 3d: SOC Vs K on Marshy soil @ phase II

Figure 3e: SOC Vs WHC on Marshy soil@ phase III

Figure 3f: SOC Vs K on Marshy soil @ phase III

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Effect of SOC in the form of amendments on hydraulic properties of arid soils Guruprasad M. Hugar

International Journal of Civil and Structural Engineering

Volume 4 Issue 3 2014

461

Figure 4a: SOC Vs WHC on Mountainous soil @ phase I  

Figure 4b: SOC Vs K on Mountainous soil @ phase I

Figure 4c: SOC Vs WHC on Mountainous soil @ phase II

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Effect of SOC in the form of amendments on hydraulic properties of arid soils Guruprasad M. Hugar

International Journal of Civil and Structural Engineering

Volume 4 Issue 3 2014

462

Figure 4d: SOC Vs K on Mountainous soil @ phase II

Figure 4e: SOC Vs WHC on Mountainous soil@ phase III

Figure 4f: SOC Vs K on Mountainous soil@ phase III

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Effect of SOC in the form of amendments on hydraulic properties of arid soils Guruprasad M. Hugar

International Journal of Civil and Structural Engineering

Volume 4 Issue 3 2014

463

4.3 Water holding capacity (WHC) SOC helped in fine particle aggregations which lead to the increment in porosity of soils. Such of the pores hosted water where in soil water is held by adhesive and cohesive forces within the soil leading to an increased water holding capacity. 4.4 BC soil In phase I humus enhanced WHC for all the inputs, it had the varying relation and however enhancement was from 1.38 times the least to 1.58 times the highest with respect to the control. Bagasseash had the varying trend with WHC it enhanced by 1.3 times the control only at threshold SOC, beyond and below threshold, WHC was reduced in comparison with control. Pressmud enhanced WHC for all its input range. WHC increased with the SOC, the highest increment was by 1.34 times the control and the least increment was 1.14 times. Flyash though improved, had the varying trend with WHC, it enhanced by 1.2 times the control only at threshold as seen in Figure 1a. In phase II humus had the varying trend with WHC it enhanced by 1.3 times the control only at threshold SOC. Bagasseash performed much better than the phase I, it increased WHC by 2.2 times the control. Increment in SOC reduced WHC as seen in Figure 1c. When BC soil column was watered there was hardly any drainage seen even after 48 hours all the water was pounded on the surface when amended with pressmud and flyash. This was because BC soil is clayey in nature that has fine pores if blended with the fine amendments it is bound to reduce the porosity and the soil amendment matrix totally clogs the soil pores thus making it totally non porous. Hence amending BC soil with pressmud and flyash is not a wise assortment. In phase III humus increased WHC with SOC only up to threshold later it reduced. Of all the phases and amendments humus in phase III improved WHC by 4.4 times. Bagasseash increased WHC with SOC only up to threshold later it reduced; it increased WHC by 1.9 times the control. Pressmud had the varying trend with WHC it enhanced 1.8 times the control. Flyash was not a good choice for phase III since WHC drastically reduced in comparison with the control, as seen in Figure 1e. Except flyash the soil and rest of amendments were non spherical in their shape resulting in non cylindrical pores which thus benefited the WHC as per the findings of Li et al. (1986); Mason and Morrow (1991). 4.5 Red soil In phase I except fly ash all the amendments improved WHC by 2 to 3 times than that of control, as seen in Figure 2a. In phase II only flyash improved WHC by 3 times, while the rest had the similar increments in the range of 1.4 to 1.9 times the control as seen in Figure 2c. In phase III performance of humus was similar as seen for BC soil in phase III; it increased WHC by 4.6 times the control. Next to it were bagasseash and flyash which increased WHC by 2.4 and 2.1 times respectively. Performance of pressmud was meager in comparison with the rest as seen in Figure 2e. Flyash was spherical and red soil was angular in its microstructure which resulted in non cylindrical pores which thus benefited the WHC this was prominently observed in phase III.

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Effect of SOC in the form of amendments on hydraulic properties of arid soils Guruprasad M. Hugar

International Journal of Civil and Structural Engineering

Volume 4 Issue 3 2014

464

4.6 Marshy soil In phase I except flyash all the amendments increased WHC in the range of 1.2 to 2.5 times. Increment in flyash decreased WHC, only threshold dosage was good in enhancing WHC for flyash as seen in Figure 3a. In phase II only flyash played a meager role in increasing WHC, while the rest had the similar increments in the range of 2.4 to 2.6 times the control as seen in Figure 3c. In phase III humus, bagasseash and pressmud respectively increased WHC to 4.2, 2.7 and 2.9 times the control. Flyash though increased WHC to 1.5 times, the increments in SOC decreased WHC, as seen in Figure 3e. Since the microstructure of marshy soil and flyash were spherical or nearly spherical WHC was little benefited. Amending marshy soil with less dense material increased the specific surface which enhanced porosity and lead to the increment of WHC. 4.7 Mountainous soil For all the three phases performance of flyash was scanty as compared with the rest. Except flyash rest increased WHC by 2 times in phase I as seen in Figure 4(a, c & e). In phase II pressmud and flyash increased WHC by 3.8 and 3 times the control. Humus and bagasseash increased by 2 times. Phase III: except flyash rest increased WHC by 4 times the control. Amongst all the amendments humus performed better than the rest in enhancing WHC as it acts as a sponge in the soil, retaining soil moisture. Next to humus it was bagasseash and pressmud that amplified WHC their angular shape was an added boon in holding water. The results showed encouraging relation between the SOC input and WHC in all the three phases up to the threshold limit of SOC dosage. This proves that increased SOC will not always be helpful in betterment of WHC. Flyash as an amendment though amplified the WHC in all the soils the amplification was scarce when compared with the rest, this is because of the increased number of fines within, which when blended or stacked did not allow the infiltration by clogging the available pores in the soil. Also the perfect spherical microstructure by its very nature makes it to loose the same completely due to percolation, thus loosing the additional benefit of angularity to retain the moisture at the edges even after drain. 4.8 Hydraulic conductivity (K) An increase in Carbon decreases soil bulk density through increased aggregation of soil particles (Hemmata et al., 2010; Elsharawy et al., 2003). The reduction in bulk density (BD) is due to the integration of soil with low density organic material. This integration leads to better aggregation thus increases the micro pore volume. The result here do not abide by the findings of Joseph et al, (2000) which states low correlations between organic carbon and soil physical properties. Humus endorse total soil porosity by microbial decomposition exudates which bind soil particles increasing porosity and hydraulic conductivity. 4.9 BC soil In Phase I pressmud increased K by 6 times while the rest increased by 3 times as seen in Figure 1 b. Pressmud by its coarse nature improved the overall porosity leading to improved hydraulic conductivity. In Phase II increment in K was by only 1.5 times the control as seen in Figure 1 d, this is probably due to blending the amendment with soil in the column for the entire depth which reduce the pore volume and decreased K. For Phase III K was Enhanced

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Effect of SOC in the form of amendments on hydraulic properties of arid soils Guruprasad M. Hugar

International Journal of Civil and Structural Engineering

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by 21 times for bagasseash ash and 17.5 times for humus, while appreciable increments were not seen for pressmud. For flyash K was negatively linked with SOC, as seen in Figure 1 f. Since the amendments were not blended, the natural pores in the amendments and the soils were not disturbed which the reason for hike in the conductivity. 4.10 Red soil In phase I bagasseash increased K by 3.5 times the control, while the rest meagerly increased K as seen in Figure 2 b, which is because of the coarse nature of bagasseash. In phase II pressmud increased K by 4 times the control, while the rest meagerly increased as seen in Figure 2 d, pressmud by its sticky nature might have bound the fines leading to the increment of pore volume. In phase III performance of humus was the supreme amongst the amendments where the increment in K was 95 times the control. Bagasse ash and pressmud increased K by 4 and 6 times respectively, while flyash enhanced only 1.5 times, as seen in Figure 2 f. 4.11 Marshy soil In phase I bagasseash and pressmud increased K by 4 times, while humus increased by only 1.5 times and flyash totally retarded, as seen in Figure 3 b. In phase II bagasseash increased by 6 times the control, while humus and pressmud increased by 2.5 times. Flyash though increased by 1.5 times; the increment in SOC was inversely related with K, as seen in Figure 3 d. In phase III humus, bagasseash and pressmud increased K respectively by 59, 21 and 11 times the control, while flyash though increased K by 13 times the increment in SOC was decreasing K, as seen in Figure 3 f. 4.12 Mountainous soil In phase I humus and pressmud by their coarse nature enhanced K by 21 and 23 times the control. Bagasseash increased K by 4 times while the increment in K with flyash though increased 1.3 times the relation of K was negative with K as seen in Figure 4 b. In phase II humus, bagasseash and pressmud respectively increased K by 17, 76 and 10 times the control, while flyash did not perform with respect to K, as seen in Figure 4 d. In phase III humus, bagasseash and pressmud respectively increased K by 200, 49 and 25 times the control, while flyash did not perform well with respect to K, as seen in Figure 4 f. Amending soils with SOC improves the soil structure by improving soil permeability, allows water infiltration, reduced runoff and erosion. Along with threshold SOC mode of blend is significant in hydraulic conductivity. Except BC soil all the soils improved ‘K’ for phase III while it was phase I for BC soil. It was humus that performed better than the rest of amendments. Application of fly ash to the soils improved hydraulic conductivity of sandy soils. Bagasseash is coarse powder with the fines within, when amended improves the hydraulic conductivity by changing the soil structure leading to increased flocculation. Beyond threshold SOC limit no satisfactory amplifications in hydraulic conductivity were observed. The only likely reason for this is the change in the soil matrix due to the high bagasse ash content displacing the clay and fines in the soil. Flyash as observed in WHC performed meager in hydraulic conductivity than the rest of amendments due to decreased micro pores, even when lowest amount of fly ash was added in the soil. 5. Conclusion

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Effect of SOC in the form of amendments on hydraulic properties of arid soils Guruprasad M. Hugar

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A series of experiments were conducted to find the effect of organic carbon on WHC and K of arid soils using various wastes as source of SOC. Soil columns in triplicate were used for the analyses for each soil amendment combination. There exists a definite threshold limit of SOC for the soil amendment combination below and beyond which no significant gains in WHC and K can be seen. Mode of application significantly affected WHC and K of soils. To improve WHC Phase III proved the best solution. This statement held true for all the soils except red soil wherein WHC was amplified by Phase I. Since the natural pores of soil were undisturbed it was again phase III mode of waste application that enhanced hydraulic conductivity for most of the soils except black cotton soil which had the better performance in phase I. SOC improved both WHC and K of all the soils irrespective of the soil type. Along with SOC it was also the microstructure of soil and amendment that has its role. Irrespective of phase and soil type, humus proved beneficial for all soils , except for red soil where flyash alone was dominant. Flyash was not a good choice for mountains soil in enhancing K. Thus SOC content alone may not be the only reason for immediate beneficial changes in soil physical and hydraulic properties. 6. References

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Effect of SOC in the form of amendments on hydraulic properties of arid soils Guruprasad M. Hugar

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