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1 Impact of long term application of rice husk ash on soil-water relations in Palakkad Eastern plains (AEU 23) Rincy Rose T. John 1 and Dr. Jayasree Sankar S. 2 1 Research Scholar, Department of Soil Science and Agricultural Chemistry, Kerala Agricultural University, Thrissur 2 Professor and Head, Department of Soil Science and Agricultural Chemistry, Kerala Agricultural University, Thrissur Abstract The soils in the Vadavannur region (Inceptisols of Udic Haplustepts) of Palakkad Eastern plains (AEU 23) of Kerala are amended with the rice husk ash (RHA) continuously for the past 30 years undertaken one of the farmers practice wherever the material is available in plenty. The present study was to attribute a rationale to the practice and to assess and relate its influence on physical and hydrological properties of soil. The soil samples were collected from both RHA amended and nonamended locations such as Vadavannur, Muthalamada and Thathamangalam. Results showed that the characters viz; bulk density, porosity, water holding capacity and organic matter were significantly improved in RHA amended locations as compared to non-amended locations over a long run. Similarly, the water infiltration rate also recorded significantly higher values in amended regions. Keywords: Rice husk ash; infiltration rate; bulk density; porosity; amendment I. INTRODUCTION Rice husk is used as a source of fuel for producing energy in the rice milling industries for processing paddy. The rice husk ash which comes out as a waste material usually gets dumped without any usage. Farmers of the experimental areas resorted to applying RHA to avoid it being a menace to the localites and to avoid environmental pollution on it gaining entry to the water bodies. This practice continued for more than three decades and a positive effect could be observed in the general status of the palm and its yield. The present study was hence taken up with the objective to unravel the influence of RHA on soil physical and hydrological properties. A bulk of soil the medium for plant growth is not all solid but has a void or empty space that is occupied by air and water. Bulk density expresses the ratio of mass of dried particles to the total volume of soil. Porosity is an index of relative pore volume in the soil. The volume percentage of the total bulk of a soil not occupied by solid particle is known as porosity. These physical properties are particularly related to the soil water and air movement. Infiltration is the process of entry of water due to sorption that happens in the soil air interface followed by vertical flow of water through soil profile. It is expressed as infiltration rate and helps in assessment of textural and structural conditions of soil surface, the ability of subsurface layers for transmitting the water and also for deciding the supply rate of irrigation water. It is one of the important dynamic flow processes in the hydrological cycle. Information dealing with the water retention, water entry from surface downward and redistribution following infiltration in the soils is of immense use for water management and conservation studies. The rating for infiltration in soil according to Bouwer [1], is presented in Table All rights Reserved Page 126

2 Table 1. Rating chart of infiltration in soil Infiltration rate (cm h -1 ) Rating > 254 Very rapid Rapid Moderately rapid Moderate 5-20 Moderately slow 1-5 Slow < 1 Very slow Among different factors, the aggregate stability had the greatest influence on infiltration rate, which in turn was closely related to organic matter content [2]. Whenever microporosity and aggregate stability get reduced the infiltration rate also becomes less. Significant differences in infiltration rates among RHA-mixed, RHA- mulched and the unamended/ mulched in loamy sand soils was reported by Essien and Saadou [3]. The RHA mixing method was also found beneficial for loamy sands to increase infiltration rate The present work was planned to study the effect of continuous application of rice husk ash on physical and hydrological properties of soil. II. MATERIALS AND METHODS The Palakkad Eastern plain (AEU 23) is the 23 rd Agro-ecological unit of Kerala, India. It represents the drier parts of Palakkad plain in the gap region of Western Ghats, having low rainfall, long dry period and fertile soils. Vadavannur and Muthalamada the two panchayats in Palakkad Eastern plain comes under Vadavannur soil series (fine- loamy, mixed isohyperthermic famiy Udic Haplustepts). A preliminary survey was conducted in the Palakkad Eastern plains to identify the areas where RHA amendment was in vogue. Following which three locations viz; Muthalamada (L1), Vadavannur (L2) and Thathamangalam (L3) could be identified where RHA application was practiced by farmers for 30 years. For getting a comparison on the advantages of an RHA addition, three locations in the near vicinity of the location were also identified, with no application of RHA. A. Soil sample collection Soil samples were collected during the period January March 2015 from two categories of fields at the rate of 10 samples and replicated thrice from each location from a depth of 15 cm. The bulk density, porosity and maximum water holding capacity were determined using Keen- Raczkowski brass cup method [4]. Bulk density = (B-A)/ V Porosity = (D-E)/ V x 100 Maximum water holding capacity = (C-B)/(B-A) x100 Where, A - Weight of Keen- Raczkowski box + filter paper B - Weight of Keen- Raczkowski box + dry soil C - Weight of Keen- Raczkowski box + saturated soil D - Weight of Keen- Raczkowski box + soil after removing expanding portion E - Weight of Keen- Raczkowski box + soil after drying in oven V Volume of the Keen- Raczkowski All rights Reserved Page 127

3 B. Measurement of infiltration rate of water in soil Infiltration rates were measured in situ at each location using double ring infiltrometer. Double ring infiltrometer consists of inner and outer cylinders having 30 cm and 60 cm diameters respectively. After removing the plants and crop residues from the surface of soil, it was slightly levelled to reduce soil disturbance to the minimum and to install the cylinders. The cylinders were concentrically installed in soil at about cm depth using a hammer. Then water was filled up to the mark initially in inner cylinder, followed by the outer one. The recession of water in the inner cylinder was recorded at a time interval of five minutes until the amount of water entering into the soil per unit time became a constant. The average infiltration rates were calculated using the data following the methodology suggested by Dakshinamurti and Gupta [5] and Michael [6]. Infiltration rate = Amount of water infiltrated Time taken The soil texture was determined by international pipette method [7]. Wet oxidation method was used for estimation of organic carbon in soil [8]. Organic matter = organic carbon x III. RESULTS AND DISCUSSION A. Soil texture As per the triangular diagram, the textural analysis of three locations in Palakkad eastern plain is given in Table 2. The textural classes were observed as sandy loam and sandy clay loam in the three locations experimented depending upon the sand, silt and clay percentage. Among the locations, no difference was observed in texture consequent to RHA addition. This is quite expected as textural classes of soil are not subjected to easy modification in the field. The textural class influences the total pore space and distribution of macro and micro pores in soil and which in turn the soils hydrological properties. The textural difference observed in different locations in this investigation may be due to the heterogeneous nature of soil system, tropical climate coupled with high rainfall and temperature [9]. Table 2. Mechanical composition of amended and non-amended soils Sand Silt Clay Category Textural class % Muthalamada (L1) Vadavannur (L2) Thathamangalam(L3) NA- RHA non- amended fields A- RHA amended fields NA sandy loam A sandy loam NA sandy clay loam A sandy clay loam NA sandy clay loam A sandy clay loam B. Characterization of soil Bulk density of Muthalamada was found to be higher (1.48 Mg m -3 ) due to the higher coarse fraction of the soils. Bulk density of Vadavannur and Thathamangalam soils were found to be lower All rights Reserved Page 128

4 it is shown in the Table 3. The high total pore volume found in the soil due to micro-aggregation of soil particle may cause lower bulk density of the soil. The RHA amended locations were recorded significantly higher values for bulk density, porosity, water holding capacity and organic matter. According to Mbagwu [10], organic waste amendment reduced soil bulk density, increased soil total porosity, which controls the water movement and gas exchange in soil. This situation also favoured the soil micro-organisms by providing the required water and oxygen. The conversion of rice husk into RHA at high temperature or the carbonization process improved the water holding capacity of the resultant material [11]. The high water holding capacity is because of the higher efficiency of RHA to absorb large amount of water. Organic matter improvement in amended area also imparts high water holding capacity of soil. Table 3. Physical characters and organic matter status of soil collected from amended and non-amended locations Bulk density Porosity Maximum water holding capacity Mg m -3 % Organic matter NA A NA A NA A NA A Muthalamada (L1) Vadavannur (L2) Thathamangalam (L3) Mean Standard deviation t value 1.37* 4.91** 2.93** 5.043** C. Infiltration rate of water Infiltration rate is recorded as a function of time. According to the infiltration rating outlined by Bouwer [1] and adopted in this study, the amended soils showed slow rate of infiltration in sandy clay loam and moderately slow rate in sandy loam soils. The amendment had a positive effect on infiltration rate (Table 4). Table 4. Infiltration rate of water in amended and non-amended soils Infiltration rate (cm h -1 ) NA A Muthalamada (L1) Vadavannur (L2) Thathamangalam (L3) Mean t value All rights Reserved Page 129

5 The increase in infiltration rate as a result of organic waste addition is dependent on factors like organic matter status [12], improved granulation [13] and pore space [14]. The higher porosity leads to improve the infiltration rate of water. When all the pores are filled with water it is said to be in saturated condition. Here the movement of water takes place in macropores, this is the reason for the water movement in sandy soil is faster than clayey soil. IV. ACKNOWLEDGEMENTS The financial assistance given by Kerala Agricultural University in the form of Junior Research Fellowship to the first author is gratefully acknowledged. BIBILIOGRAPHY [1] Bouwer, H Intake rate: cylinder infiltrometer. In: Klute, A.(ed.), Methods of soil analysis part I. Agronomy No. 9, American Society of Agronomy, Madison, USA. pp [2] Wood, M. K. and Blackburn, W. H Sediment production as influenced by livestock grazing in the Texas Colling plains. J. Range Manag. 34: [3] Essien, O. E. and Saadou, A Infiltration and sorptivity response to application rice-husk-ash amendment of loamy sand soil in Ikpa Basin, Nigeria. Res. J. Appl. Sci. Eng. Technol. 4: [4] Piper, C. S Soil and Plant Analysis (Asian Reprint, 1966). Hans Publishers, Mumbai, India, 450 p. [5] Dakshinamurthi, C. and Gupta, R. P Practicals in Soil Physics, IARI, New Delhi, pp [6] Michael, A. M Irrigation Theory and Practices (2 nd Reprint). Vikas Publishing House. New Delhi, 802p. [7] Robinson, G. W A new method for the mechanical analysis of soils and other dispersions. J. Agric. Sci. 12: [8] Walkley, A. J. and Black, I. A Estimation of soil organic carbon by chromic acid titration method. Soil Sci. 31: [9] Antony, P. C Studies on the physical properties of the major soil groups of Kerala with special with salinization and desalinization. Ph.D.(Ag) thesis, Kerala Agricultural University, Thrissur, 195p. [10] Mbagwu, J. S. C Effect of organic amendment on some physical properties of a tropical ultisol. Biol. Wastes. 27: [11] Oshio, H., Nii, F., and Namioka, H Characteristics of Kuntan (rice hull charcoal) as medium of soilless culture. J. Japan. Soc. Hortic. Sci. 50: [12] Foth, H. D Fundamentals of Soil Science (6 th Ed.). Wiley, New York. [13] Anjaiah, N., Venekaiah, K., Rao, M. S., and Venkateswarlu, M. S Effects of amendments on physical properties of soil under rainfed cultivation. Int. Agrophys. 3: [14] Prove, B. G., Loch, R. J., Foley, J. L., Anderson, V. J., and Younger, D. R Improvements in aggregation and infiltration characteristics of a Krasnozem under maize with direct drill and stubble retention. Aust. J. Soil Resour. 28: All rights Reserved Page 130