Browsing by Author "Rashbi Jahan, V"

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    Spatial variability and dynamics of arsenic in selected coastal rice ecosystems of Kerala
    (Department of Soil Science and Agricultural Chemistry, College of Agriculture, Vellanikkara, 2025-02-12) Rashbi Jahan, V; Mayadevi, M R
    Arsenic (As) is a naturally occurring toxic metalloid, that can cause detrimental effects on plants as well as humans. Though the elevated level of As is not reported from the paddy soils of Kerala, the tropical climate and high amorphous Fe minerals in the soil may cause an excessive dissolution of arsenic in the soils of Kerala. Hence, a study entitled “Spatial variability and dynamics of As in selected coastal rice ecosystems of Kerala” was designed to understand the spatial distribution of As in paddy soils of coastal agroecological units (AEU), namely, Northern coastal plain (AEU 2) and Kaipad lands (AEU 7) and to study the effects of agricultural amendments such as lime and organic manure on As content in these soils. Thirty-eight and eight georeferenced, grid-based (5 x5 km2) irrigation water and soil samples each were collected from paddy fields of panchayats under the Northern coastal plain (AEU 2) and Kaipad lands (AEU 7), respectively, at a sampling intensity of one panchayat from one grid forming a total of ninety-two samples. The pH of irrigation water from AEU 2 varied between 5.94 and 8.58, and that of Kaipad lands (AEU 7) from 7.46 to 8.6. The electrical conductivity (EC) of AEU 2 varied from 0.03 to 4.59 dS m-1 and between 0.02 and 17.02 dS m-1 from AEU 7. The content of As in irrigation water ranged from 0.02 µg L-1 (Feroke, Kozhikode) to 1.56 µg L-1 (Matool, Kannur) in AEU 2. In AEU 7, the lowest and highest As reported were 0.08 µg L-1 (Cheruvathur, Kasaragode) and 4.67 µg L-1 (Ezhome, Kannur), respectively The pH of the soils of the Northern coastal plain (AEU 2) varied from 3.08 to 7.42, and EC from 0.05 dS m-1 to 4.46 dS m-1. The organic carbon varied from 0.19 per cent to 5.33 per cent. The pH of soil from Kaipad lands (AEU 7) varied from 4.2 to 7.23; EC from 0.05 dS m-1 to 12.12 dS m-1. The organic carbon varied between 0.31 per cent and 3.94 per cent. The available As in soils of AEU 2 varied from 0.65 µg kg1 (Chorodu, Kozhikode) to 832.87 µg kg-1(Vallikkunnu, Malappuram) and showed a significant negative correlation with available Iron (Fe) (r = -0.369*), Phosphorus (P) (r = - 0.351*), and a significant positive correlation with available Calcium (r = 0.384*), Magnesium (r = 0.432**). The available As in soils of Kaipad lands varied from 0.35 µg kg-1 at Pilicode to 1255.2 µg kg 1 at Pallikkara, Kasaragod. However, none of the samples reported As content more than the prescribed critical limit of 100µg L-1 set by the Food and Agricultural Organization for irrigation water and 5800 µg kg-1 set by the Geological Survey of India for agricultural soils. The total As in soils of AEU 2 varied from 1.5 mg kg-1 (Chemnad, Kasargode) to 37 mg kg-1(Vallikkunnu, Malappuram), and that of AEU 7 from 6.5 mg kg-1(Pilicode, Kasargode) to 36.5 mg kg-1(Pallikkara, Kasaragode) and was positively correlated (r = 0.639***) with available As. Results revealed that 58 % (N=38) of soil samples from AEU 2 and 25% (N=8) from AEU 7 recorded more than the critical limit of 20 mg kg-1 of total As recommended by The European Union and Agency for Toxic Substances and Disease Registry (ASTDR) for agricultural Soils. A batch incubation study was conducted to study the effects of lime (fine lime powder) and organic manure (cow dung) on available arsenic content for 30 days, and chemical analyses were done at 1,3,5,10,15 and 30th day of incubation. The composite soil samples from AEU 2 and 7 were spiked individually with As at 400 mg kg-1 of soil and were used for the study. The As spiked soils were incubated with lime at 600 kg ha-1 (T2) and 1200 kg ha-1 (T3), organic manure at 5t ha1 (T4), 10t ha-1 (T5) and a combination of lime at 600kg ha-1 and fresh cow dung at 5t ha-1 (T6) against As spiked soil as control (T1). The combined application of lime at 600 kg ha-1 and organic manure at 5t ha-1 (T6) significantly increased the soil pH of the AEU 2 from the 15th to 30th day of incubation, whereas in AEU 7, lime at 1200 kg ha-1 (T3) significantly (p=0.05) increased the pH up to 30th day of incubation. Irrespective of the AEUs, the highest reduction in available Fe was recorded in lime-amended soils at 600 kg ha-1 from the 10th to the 30th day of incubation and available As exhibited a significant negative correlation with available Fe in soils of Northern coastal plains under organic manure amendment. Irrespective of the AEUs, the organic manure at 10t ha-1 significantly increased the available P content up to 15th day of incubation. Irrespective of AEUs, the highest available As was recorded by control soil (T1) up to the 30th day of incubation. A significant reduction in available As was reported from T5 (organic manure at 10 t ha-1) up to the 10th day of incubation in AEU 2. However, irrespective of AEUs, the combined application lime and organic manure (T6) significantly reduced the available As up to 30th day of incubation. Hence, incubation study of arsenic dynamics under liming and organic manure regimes revealed that the application of soil amendments like lime and organic manure effectively reduced available As in soils of the Northern coastal plain and Kaipad lands. Also the sources and dynamics of geogenic and anthropogenic As and its contributing factors in agricultural systems need to be studied extensively.