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Effect of Ionic Concentration on Ion Sorption Behaviour in Five Soil Series of Bangladesh

M. R. Khanam
Department of Soil Science, Bangladesh Agricultural University, Mymensingh-2202

M. J. Abedin Mian
Department of Soil Science, Bangladesh Agricultural University, Mymensingh-2202

M. N. Bari
Entomology Division, Bangladesh Rice Research Institute, Gazipur-1701

M. Mofazzel Hossain
Entomology Division, Bangladesh Rice Research Institute, Gazipur-1701

M. J. Uddin
Soil Science Division, Bangladesh Rice Research Institute, Gazipur-1701

Abstract/ Executive Summary:

Combined effect of ion sorption behavior of five soil series of the Agro-ecological zone of Old Brahmaputra Floodplain was carried out. The amount of ion sorbed by soil under recommended doses of N. P. K and S fertilizers were applied at different ion concentration. Result shows that there was a wide variation in ion sorption for different soils, times as well as ion concentration. In general. the sorption of different cations and anions increases with the increase of ionic concentration of the solution i.e., the increase of ionic strengths. The sorption of Ca²⁺ was the highest in all soils followed by NH₄⁺ and K⁺. Among the anions the phosphorus sorption occurred highest followed by NO₃^- and SO₄^2-. The soils of Ghatail soil series sorbed the highest amount of cations and anions and the soils of Tarakanda soil series sorbed the lowest amount because of textural variation. organic matter content, soil reaction as well as cation exchange capacity. The amount of ions sorbed by Sonatola, Shilmandi and Lockdeo soil series was almost equal. Maximum sorption of K⁺ and NH₄⁺ was found in saturated condition (medium concentration) in Shilmandi and Lockdeo soils. In case of other soils, the maximum ion sorption was found at/field capacity (high concentration).

Keywords: Anion, Cation, Field capacity, Moisture and Saturated

Location: Department of Soil Science at Bangladesh Agricultural University, Mymensingh

Start Date: 00-07-1996

End Date: 00-12-1996

Program Area: Crop-Soil-Water Management

Commodity: Soil fertility

Objectives:

Objective of the study was to investigate the combined effect of ion sorption behavior of five soil series under different ion concentrations.

Methodology:

The experiment was conducted in the laboratory of the Department of Soil Science at Bangladesh Agricultural University, Mymensingh from July 1996 to December 1996. Soil samples at a depth of 0-15 cm were collected from five different places, under the Agro-ecological Zones of Old Brahmaputra Floodplain with the help of a core sampler. The collected soils were air dried, ground and passed through a 2 mm sieve. Soil Analysis: Mechanical analysis of soils was performed following hydrometer method (Buoyoucos 1926) and the textural class was determined by plotting the values of % sand, % silt and % clay to the Marshall's triangular coordinates. Particle density of soil was determined by the method followed by Black (1965). Soil pH was measured by glass electrode pH meter using soil:water ratio of 1:2.5 (Jackson 1962). EC was measured by conductivity meter soil: water ratio of 1:5; available sulfur was determined by extracting the soil samples with CaCl₂ solution (0.15%) and Cation Exchange Capacity (CEC) of soils was determined following the sodium saturation method. The ionic strengths of equilibrium soil solution were calculated following the formula 0.013 EC in m mohs cm^-1. Organic carbon was estimated by wet oxidation method as described by Black (1965) and the organic matter content was calculated by multiplying the percent organic carbon with the Van Bemmelen factor, 1.73. The concentration of NH₄-N and NO₃-N in the extract was determined by distillation method using successively MgO and Deverda alloy for NH₄-N and N0₃-N, respectively. Available phosphorus was estimated by extracting the soil P with 0.5 M NaHC0₃ solution having pH 8.5. The extracted P was then determined colorimetrically by SnCl₂ reduced phosphomolybdate blue colour method. The amount of S in the extract was estimated turbidimetrically by spectrophotometer at 420 nm. Exchangeable K and Ca were determined by flame photometer from the NH₄0AC extract following method described by Jackson (1962). Moisture content at different ion concentrations: The saturated samples were kept in a soil moisture extractor at 0.33 bar pressure until an equilibrium condition was established. The moisture content at field capacity was then determined gravimetrically. The water content at saturated condition was also calculated considering the differences in weight between saturated condition and oven dry weight of soil.The volume of water per square meter at 5 cm water depth was added with volume of water at saturated condition to get the water content at 5 cm standing water. Preparation of multi-ion solution for sorption study: Ion solutions of NH₄⁺,. K⁺, Ca²⁺. P (HPO₄^2- H₂P0₄^-), SO₄^2- and N0₃^- of three different concentrations were prepared by dissolving calculated amounts of NH₄N0₃. CaS0₄. 2H₂0, Ca(H₂P0₄)₂. H₂0 and KCl salts in water. The different doses of fertilizers considered for this study were 100 kg N/ha, 60 kg P/ha, 40 kg K/ha and 30 kg S/ha. As this salt contained N0₃^- and ca²⁺, the concentrations of these ions in solutions were also calculated and their sorption also studied. Sorption study: Five sets of plastic bottles with three replications were prepared for 5 different times i.e., 5, 10, 24, 48 and 72 hours for each of low, medium and high concentrations. As a result 3 x 5 x 3= 45 bottles for each soil and 45 x 5= 225 bottles for five soil samples were used for the study. Eight gram of soil was taken in each of the 45 bottles earmarked for each soil. Of these 45 bottles, 15 were earmarked for sorption solution of low concentration, 15 for medium concentration and 15 for high concentration. Eighty ml of respective sorption solution was added to each of 15 bottles, shaken for 30 minutes in a horizontal shaker and allowed to stand for above mentioned time for sorption. Three separate bottles were kept for each time. At the end of allocated time, the suspensions were filtered through a retentive filter paper and the concentration of NH₄-N, N0₃-N, SO₄^2-, P, K⁺ and Ca²⁺ in the equilibrium solutions were determined following the method as stated above.

Source of Information: J. Asiat. Soc. Bangladesh, Sci, 29(1): 121-132, June 2003

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Achievement/Findings:

The present study revealed that the highest sorption of K⁺ and NH₄⁺ occurred at medium concentration, while at high concentration the sorption of Ca₂⁺ and different anions was the highest. It could be said that at field capacity (high concentration), the Ca²⁺ displaced the NH₄⁺ and K⁺ from exchange sites and get sorbed. But at saturated condition all the anions and cations was sorbed in reasonable amounts without any disturbance to one another. The soils of Ghatail soil series sorbed the highest amount of cations and anions and the soils of Tarakanda soil series sorbed the lowest amount because of textural variation, organic matter content, soil reaction as well as cation exchange capacity. The amount of ions sorbed by Sonatola, Shilmandi and Lockdeo soil series was almost equal. Maximum sorption of K⁺ and NH₄⁺ was found in at saturated condition (medium concentration) in Shilmandi and Lockdeo soils. In case of other soils, the maximum ion sorption was found at field capacity (high concentration).

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