Different fractions of iron in paddy growing soils in selected villages of Gangavati taluka in North Karnataka, India

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1 Agric. Sci. Digest., 35 (3) 2015: Print ISSN: X / Online ISSN: AGRICULTURAL RESEARCH COMMUNICATION CENTRE Different fractions of iron in paddy growing soils in selected villages of Gangavati taluka in North Karnataka, India S. Selvaraj* and B. Basavaraj Department of Soil Science and Agricultural Chemistry, College of Agriculture (UAS), Dharwad , India. Recieved: Accepted: DOI: / ABSTRACT Sixty surface (0-20 cm) soil samples each from the farmers paddy field collected from different villages of Gangavati taluka in North Karnataka in the year The two years soil samples were pooled and handled for laboratory analysis. Fractionation of iron in soil samples carried out with standard procedure. Distributions of different forms of iron in twelve village paddy growing soils were studied. The results showed that more than 31.48% in Karatagi sample and 71.91% in Maralanahalli sample of total iron occurred as free and amorphous bound iron, where as water soluble iron occurred only in 0.03% in Karatagi sample and 1.17% in Rampura soil samples. Soil contained water soluble iron from 0.11 to 4.62 ppm, exchangeable iron from 0.22 to 3.93 ppm, amorphous iron oxide bound iron from to ppm, crystalline iron oxide bound iron from to ppm and residual iron to ppm. In this fractions water soluble and exchangeable iron was low in all the soils when compared to other fractions, still it is very important from the plant availability point of view. Amorphous iron oxide bound form of iron dominated when compared to water soluble iron, exchangeable iron, crystalline iron oxide bound iron and residual iron fractions. Key words: Amorphous iron oxide bound iron, Crystalline iron oxide bound iron, Exchangeable iron, Iron fractions, Paddy soil, Residual Total iron, Water soluble iron. INTRODUCTION Rice is India s most prominent crop and the staple food of the people of the eastern and southern parts of the country. The term rice is life is most appropriate for India as this crop plays vital role in country s food security and provides livelihood for millions of rural households. Rice fields in India cover an area of Mha. Rice production in India had reached 151 MT and India stands second in production in the world only after China (Anonymous, 2010). Rice is one of the major staple food crops of Karnataka and grown at different agro-climatic zones, occupying an area of 14.5 lakh ha. Though rice stands second in area, it ranks first in production (36.58%) among the cereal crops in Karnataka. The use of fertilizer particularly micronutrients are the part of modern rice cultivation and their use greatly enhanced in rice production. Increased micronutrient demands for intensive cropping practices and adoption of high yielding cultivars may be one of the reasons for deficiency of Fe in the paddy soil (Fageria et al. 2002). With the awareness among farmers about the menace of micronutrients deficiency particularly Fe, the use of iron sulphate has increased in the country and the extent of the deficiency is changing over the years (Nayyar et al. 2001). Therefore, an attempt made to study the distribution of different iron fractions in paddy growing soils of Gangavati taluka in North Karnataka. MATERIALS AND METHODS Location of the experimental site: Sixty surface (0-20 cm) soil samples each from the farmers paddy field collected from different villages of Gangavati taluka in North Karnataka in the year From one village five farmer fields were selected and soil samples were collected from each field. Soil samples collected from Vadratti, Basapatna, Karatagi, Mallapura, Marali, Siddhapura, Maralanahalli, Herura, Sangapura, Anegunti, Sanapura and Rampura villages in Gangavati taluka of Karnataka state. The soil samples collected villages are given in location map of study area in Fig. 1. Collection and analysis of soil samples: The surface (0-20 cm) soil samples from each village were taken using a 5 cm diameter auger, after harvest of paddy crop these soil samples mixed thoroughly, air dried in shade and crushed to *Corresponding author s selvaraj147@gmail.com. Present address: Don Bosco College of Agriculture, Sagayathottam,Vellore , Tamil Nadu.

2 168 AGRICULTURAL SCIENCE DIGEST Location of villages 1 Vadtratti 7 Maralanahalli 2 Basapatna 8 Herura 3 Karatagi 9 Sangapura 4 Mallapura 10 Anegundi 5 Marali 11 Sanapura 6 Siddhapura 12 Rampura FIG. 1: Location map of selected villages in Gangavati taluka pass through 2 mm sieve and stored in sealed polythene covers for analysis. The pooled soil samples were used for iron and their fractions study in paddy ecosystem. The soils were analyzed for ph, EC and Organic carbon, CaCO 3 with standard methods. Fractionation of soil iron was carried out with standard procedure. For determining DTPA-extractable Zn content, soil samples were taken at harvesting of paddy was determined from 1:2 soil-extractant ratio using DTPA- TEA buffer (0.005 M DTPA M CaCl M TEA, ph 7.3) and concentration of Fe was measured on an atomic absorption spectrophotometer Varian AA 240FS by Lindsay and Norvell, (1978). Sequential extraction of soil samples for different fractions: The processed soil samples were used to fractionate Fe into following chemical fractions as per sequential procedure described below. Water soluble iron: One g soil was extracted with 40 ml double distilled water (maintaining soil to water ratio of 1:40) and equilibrating for 16 hours by shaking in a mechanical

3 Volume 35 Issue 3 (2015) 169 TABLE 1. Basic characterization of soils in Paddy ecosystem from farmer fields in Gangavati taluka Village ph(1:2.5) EC(dSm -1 ) Organic carbon(g kg -1 ) CaCO 3 (<2 mm)(%) Vadratti Basapatna Karatagi Mallapura Marali Siddhapura Maralanahalli Herura Sangapura Anegunti Sanapura Rampura Mean shaker. Iron in the extract was determined by Atomic Absorption Spectrophotometer (Miller et al. 1986). Exchangeable iron: Soils were extracted with NH 4 OAc solution and shaken mechanically for 1 hour and centrifuged. Clear solution was collected and NH 4 -saturated soil was washed with three times with 20 ml 95 per cent ethanol, by shaking and centrifugation. Hundred ml volume of the solution was used for exchangeable iron estimation by Atomic Absorption Spectrophotometer (Thomas, 1982). Crystalline iron oxide bound iron: Citrate bicarbonate dithionate (CBD) method was followed to extract free iron oxide from soil samples. Soil samples were heated at 70 o C with citrate-bicarbonate buffer (1:5 to soil: buffer). At soil suspension temperature of 75 o C, 1g of sodium dithionite was added once and stirred intermittently. The suspension was cooled, centrifuged and supernatant was collected. The residue was washed with citrate-bicarbonate and NaCl (twice) and the supernatant was collected. Iron in the washing which was made to a known volume was estimated using Atomic Absorption Spectrophotometer (Mehra and Jackson, 1960). Amorphous iron oxide bound iron: One part of soil and 40 part of oxalate reagent (ammonium oxalate + oxalic acid) was stirred and kept in darkness for 4 hours. Later centrifuged (3000 r.p.m) and iron in the supernatant were measured in an atomic absorption spectrophotometer (Miller et al. 1986). Residual iron: Residual iron fraction was calculated by taking difference of total and summation of other iron fractions. Total iron: Total iron was determined by digesting the soil sample with hydrofluoric acid in Teflan beakers. 100 mg of soil sample was transferred into 250 ml Teflan beaker, 2 ml of aqua-regia was added to disperse the sample. Later, exactly 10 ml of hydrofluoric acid was added and the contents were shaken to dissolve the sample for a period of 2-8 hours and it was dissolved using saturated solution of boric acid and was subsequently used for determination of total iron by Atomic Absorption Spectrophotometer (Page et al. 1982). RESULTS AND DISCUSSION Chemical properties of soils:the chemical properties of soil like ph, electrical conductivity, organic carbon and CaCO 3 were estimated (Table 1). Soil ph value varied in the range from 7.12 (neutral soil) in Mallapura sample to 8.54 (slightly alkaline soil) in Karatagi sample with mean ph The Electrical conductivity value ranged between 0.10 dsm -1 in Vadratti and Karatagi samples and 0.32 ds m -1 in Rampura soil sample with mean value 0.21 dsm -1. All the soil samples in Gangavati taluka had shown low electrical conductivity indicating that soils are non-saline in nature. The organic carbon content varied in the range from 1.02 g kg -1 in Sanapura sample to 9.46 g kg -1 in Rampura sample with mean value 7.23 g kg -1. Low organic carbon content might be due to continuous cultivation without regular application of FYM. The higher content of organic carbon in surface soil could be attributed to in situ incorporation of rice stubbles and addition of organic manures. Higher content of organic carbon, better aeration as well as finer fractions of soil loading to increase in the surface area for ion exchange (Sharma and Choudhry, 2007). The CaCO 3 values were in the range between 2.11 per cent (Basapatna sample ) and 9.97 per cent (Vadratti sample) in soil samples with mean value 7.82 per cent. It might be due to downward movement of calcium and its subsequent precipitation as carbonate and / or decomposition of calcium carbonate. Available (DTPA- extractable) Iron: DTPA iron measured in overall villages differed from 2.13 ppm in Anegunti soil sample to 4.99 ppm in Herura soil sample with average DTPA- Fe 3.28 ppm. Mortvedt et al. (1977) explained that the organic matter is reported to be the main source of plant available forms of Fe in soil. The wide incidence of Fe deficiency irrespective of total Fe in the soils.

4 170 AGRICULTURAL SCIENCE DIGEST TABLE 2: Iron fractions in Paddy soils of selected village in Gangavati taluka (ppm) Samples DTPA Water Soluble Exchangeable Amorphous iron Crystalline iron Residual Total Fe Fe Fe oxide bound Fe oxide bound Fe Fe Fe Vadratti village Basapatna village Karatagi village Mallapura village Marali village Siddhapura village Maralanahalli village Herura village Sangapura village

5 Volume 35 Issue 3 (2015) 171 Anegunti village Sanapura village Rampura village Mean Distribution of Iron fractions: Different iron and their fractions are given in Table 2. Water soluble iron: The water soluble iron varied between 0.11 ppm in Karatagi soil and 4.62 ppm in Basapatna soil sample with mean value 2.10 ppm. Kundu et al. (2000) explained that under nonflooded rice conditions, concentrations of water-soluble Fe were very low in both Maahas and Burabod soils. Soils reduction brought on by flooding increased Fe solubility in that soils. On flooding, Fe concentration in the acid-sulphate soil increased to reach a peak of 377 mg l -1. Exchangeable iron:the Gangavati taluk village soil samples varied in exchangeable iron from 0.22 ppm in Anegunti sample to 3.93 ppm in Marali sample with mean value 2.28 ppm. Singh et al. (2008) explained that the per cent contribution of iron towards the total Fe pool range of between and 0.002% in Agro- Eco- Sub region of Eastern Rajasthan. Amorphous iron oxide bound iron: Amorphous iron oxide bound Fe fraction was ranged between ppm in Basapatna soil and ppm in Marali soil with average value ppm. Nayak et al. (2002) noted that the red and lateritic soils contain the highest amounts of free iron oxides ranging from 640 to 1750 mg / 100 g throughout the profile while the soils in Indo-Gangetic plain contain 260 to 930 mg / 100 g soil. Crystalline iron oxide bound Fe: The Crystalline iron fraction varied in the range from ppm in Anegunti sample and ppm in Vadratti sample with mean value ppm. Basappa (1990) found that the crystalline iron oxide bound iron was in the range of 927 to1575 mg kg -1, constituting 1.98 to per cent of total iron content of soil bodies. Besides, indicated that the association of this fraction with the oxides of iron and manganese. Residual Fe: Residual iron ranged between ppm in Anegunti soil sample and ppm in Marali soil sample with average value ppm. Tessier et al. (1979) found that more than 50 per cent of the total iron was in the residual fraction mostly in primary and secondary minerals present within their crystal structure. Total Fe: The Total Fe fraction varied from ppm in Basapatna sample to ppm in Mallapura sample with mean value ppm. Katyal and Agarwala (1982) reported that the total iron varied between 1.29 and 9.86 per cent with an average of 3.3 per cent in some bench mark soils of India. By and large it was shown that heavy clay soils contained relatively higher concentration of iron, which was negated by high ph. Generally, in rice growing soils it increased with the depth. CONCLUSION Based on the study concluded that different fractions of soil iron are in dynamic equilibrium with each other. The content of different iron fractions differed between soils of selected villages in Gangavati taluka. However, the order of preponderance of iron fractions remained same viz., water soluble iron< exchangeable iron < residual iron< crystalline iron oxide bound iron< amorphous iron oxide bound iron in selected village samples. Depletion of water soluble and exchangeable iron and complexed forms of iron occurred with a build-up of residual iron, crystalline iron oxide bound iron and amorphous iron oxide bound iron occurred. ACKNOWLEDGEMENT First and corresponding author is extremely grateful to the ICAR, New Delhi for providing senior research fellowship in his study time and carry out the part of this present study.

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