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Iron and Zinc Dynamics in Submerged Soils

M. A. H. Palash
Department of Soil Science, Uniuersity of Dhaka, Dhaha-1000, Bangladesh

M. S. A. Hossain
Department of Soil Science, Uniuersity of Dhaka, Dhaha-1000, Bangladesh

A. H. Khan
Department of Soil Science, Uniuersity of Dhaka, Dhaha-1000, Bangladesh

S. Hoque
Department of Soil Science, Uniuersity of Dhaka, Dhaha-1000, Bangladesh

A. Islam
Department of Soil Science, Uniuersity of Dhaka, Dhaha-1000, Bangladesh

Abstract/ Executive Summary:

Rice (Oryza sativa L.) is almost universally grown on submerged soil. Chemical properties that prevail under aerated conditions undergo a drastic change upon submergence. Submergence reduces the soil and consequently, the oxidized chemical species viz. SO₄²_^-, NO₃-, Fe³⁺ and Mn⁴⁺ are replaced by their reduced counterparts - S²^-, NH₄+, Fe²⁺ and Mn²⁺, respectively. The pH of acid soils increases on flooding, whereas the opposite trend is found in calcareous and sodic soils. The pH profoundly influences hydroxide, carbonate, sulfide, phosphate and silicate equilibrium in paddy soils. Those equilibrium regulate the precipitation and dissolution of solids, the sorption and desorption of ions, the concentrations of such nutritionally significant elements like phosphorus, iron, aluminum, copper, zinc, hydrogen sulfide, carbonic acids and organic acids.

Keywords: Iron dynamics, Zinc dynamics, Submerged soil

Location: Kalma and Gopalpur soils of Bangladesh

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Soil fertility

Objectives:

To determine the Iron and Zinc Dynamics in Submerged Soils.

Methodology:

Incubation and pot experiments with rice were conducted on Kalma (Aeric Albaquepts), Silmondi (Aeric Haplaquepts) and Gopalpur (Aquic Eutrocrept) soils. Bulk soil samples were collected from farmers' fields to a depth of 0 to 15 cm from the soil surface. Kalma series includes seasonally flooded poorly drained soils developed in pale-coloured, highly porous, silty weathering products of the Madhupur clay. Silmondi series comprises seasonally flooded, poorly drained soils developed in moderately fine textured Brahmaputra alluvium. Gopalpur series comprises intermittently and seasonally flooded, somewhat poorly drained, olive to olive-brown soils occurring mainly on the young Ganges floodplain. Some physical and chemical properties of the soils are presented. Plastic pots (10 cm tall and 18 cm diam) were used for the incubation study. To collect the soil solution, a glass tube was fitted at the bottom of the pot. The end of the tube, inside the pot, was covered with a thin cloth. A half kg of quartz sand (washed with 6 N HCI and deionized H₂O) was placed in the pot and on top of it 1kg of air dried, ground and sieved (2 mm) soil sample was placed. There were three replications for each soil. Soil in the pot was submerged with distilled water and a constant 5 cm water head was maintained on the soil surface during 60 days of incubation period. Soil solution was collected from the bottom of the pot at 0, 1,3,7, 15, 30 and 60 days of submergence. Soil solution was analyzed for Fe and Zn contents immediately after sampling. The pot experiment was conducted in a randomized block design with three soils and six replications. Seven kg of air dried, ground and sieved (2 mm) soil was taken in an earthen pot of 20 cm height and 36 cm diam. N, P and K were applied at the rate of 70, 30 and 20 kg/ha, respectively. Rice (BR-1) seedlings of 30 days old (3 seedlings per hill and 3 hills per pot) were transplanted. The soils were kept submerged during the experiment. Soil solutions were collected from the bottom of the pots at 0, 3, 7, 15, 30 and 60 days of submergence. The collected solutions were analyzed immediately for Fe and Zn. Soil samples were analyzed for physical and chemical parameters using standard methodology. The most important chemical change that takes place in a flooded soil is perhaps the reduction of iron and the accompanying increase in its solubility. In Kalma and Gopalpur soils the concentration of water-soluble iron increased with time till 30 days of submergence and after that it decreased. In Silmondi soil the concentration gradually decreased till 15 days of submergence. The peak values were 0.28, 0.46 and 0.25 µg/ml for Kalma, silmondi and Gopalpur soils, respectively and the peaks were found at 30 days after submergence.

Source of Information: Dhaka Univ. J. Biol. Sci. 10(1) : 113-116, 2001 (January)

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The pot experiment showed the same trend, the peak value of 0.27 µg/ml was found after three days of submergence for Kalma and Gopalpur soils. The concentration decreased gradually and at 60 days of submergence it reduced to only 0.01 µg/ml. In the Silmondi soils the peak value to 0.26 µg/ml was observed just in a day of submergence and then it decreased gradually to 0.02 µg/ml at the end of 60 days of submergence. Patric and Reddy(7) suggested that the decrease in Zn concentration may be due to precipitation of Zn(OH)2 as a result of increased pH after flooding, precipitation of ZnCO₃ due to CO₂ accumulation resulting from organic matter decomposition and precipitation of ZnS under very reduced soil condition.

Knowledge Management: Journal