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Potassium Availability in Relation to Mineralogy in Some Floodplain Soils of Bangladesh.

Z. H. KHAN
Department of Soil, Water & Environment, University of Dhaka, Bangladesh.

M. S. HUSSAIN
Department of Soil, Water & Environment, University of Dhaka, Bangladesh.

M. M. HASSAN
Department of Soil, Water & Environment, University of Dhaka, Bangladesh.

Abstract/ Executive Summary:

Potassium originates in soils from some primary minerals such as orthoclase, muscovite and bioti te and in altered phyllosilicate such as illite. As K is the third most important nutrient element it is studied in soils on the basis of its availability to plants . Potassium in soil is classified in three forms: unavailable, slowly available and readily available or exchangeable. Crystalline or unavailable K comprises approximately 90 - 98% of total soil K. Slowly available potassium, which is fixed and non-exchangeable, is the form trapped between the layers or sheets of certain kinds of clay minerals. Readily available potassium is a dissolved form of K (water soluble) or held on the surface of clay particles (exchangeable K). A dynamic equilibrium exists between the different forms of K in soils. Availability of K for plants therefore depends on weathering of K bearing minerals in soil system, release of exchangeable K from the inorganic colloidal complexes, the nutrient adsorption capacity and adsorption maxima of the organic colloids present in soil system. Information on clay mineralogy is therefore crucial in understanding the K status and its release in 'soil system to meet the demands of plants. Mineralogical composition of soils has a vital influence on K dynamics. Relationships between clay mineralogy and potassium forms can be utilized in evaluating potential soil K availability, prediction of K cycling as well as its uptake by plants. Knowledge on the NH40Ac-K form of potassium along with information of clays' mineralogical composition can provide reliable information in the equilibrium and release of non exchangeable K to plants and the need for applying fertilizers containing K. Information regarding various forms of potassium in relation to mineralogy on the extensively cultivated soils of the floodplain in Bangladesh is only sporadic even today P . 2l. No study in these soils linking K release with soil mineralogy has been reported so far. The present study is an attempt to provide information on potassium in relation to mineralogy in some floodplain soils of Bangladesh .

Keywords: Potassium,Mineralogy,Flood plain,Soil

Location:

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Fertilizer

Objectives:

To provide information on potassium in relation to mineralogy in some floodplain soils of Bangladesh .

Methodology:

Nine surface (0 - 15 cm depth) soil samples representing nine typical soil series from the Ganges, Brahmaputra and Meghna floodplains of Bangladesh were collected for this study. The collected soil samples were analyzed to determine different forms of K e.g. water soluble(³⁾, exchangeable (extracted with IM NH₄0Ac) ₍₄), and non-exchangeable or fixed K (extracted with boiling lM HNQ₃)(⁵). Total K was determined through digestion of soils with Na₂CO₃ fusion method. Potassium in minerals was calculated as the difference between total potassium and the sum of all extractable potassium. Flame photometer was used for potassium determination. Bulk and clay mineralogical composition of soils were determined following the method of Jackson(⁶).

Source of Information: Dhaka Univ . J. Biol. Sci. 22(1): 79-83, 2013 (January)

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Results showed that the Gangetic floodplain soils predominated with 18 A vermiculite > illite > smectite minerals contained higher amount of all forms of potassium compared to the Brahmaputra and Meghna flood plain soils in which illite and kaolinite predominated.

Knowledge Management: Journal