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Comparison of Methods to Evaluate K Availability in Rice Soils

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

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

R. Mandal
Department of Soil Science, University of Dhaka, Dhaka-1000, Bangladesh.

S. A. Chowdhury
Department of Soil Science, University of Dhaka, Dhaka-1000, Bangladesh.

Abstract/ Executive Summary:

Eleven extractants covering acids, bases and buffer solutions have been used to evaluate K availability from 29 rice soils. Of the methods, boiling 1N HNO₃ extracted the highest amount of available K. the methods may be arranged as boiling 1N HNO₃> hot 1.4N H₂SO₄>1N Na₂SO₄ (pH 1)> modified 1N NaCl (pH 1)> 0.7N HCl> 0.5N HCl> Morgan’s reagent> 0.5M NaHCO₃ (pH 8.5)> 1N NaCl> 1N NH₄OAc> water according to their relative efficiency. Extractants having acidic characters were found to be superior over other methods. pH fluctuations possibly accentuated K release from the soils. All the methods correlated significantly with 60 days plant K. Highly significant correlation at 0.1% level as revealed by boiling 1N HNO₃, hot 1.4N H₂SO₄, 1N NaCl (pH 1) and 0.5M NaHCO₃ (pH 8.5) with plant K. Only 1N NaCl (pH 1) extractable K showed significant correlation with 90 days plant K

Keywords: Soil, Fertilizer, K, Rice

Location: Department of Soil Science, University of Dhaka, Dhaka-1000, Bangladesh.

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Soil fertility

Objectives:

To identify the comparison of methods to evaluate K availability in rice soils.

Methodology:

Surface soils (0-15 cm) from 29 soil series were collected, air dried, ground and passed through 2 mm sieve for mechanical and 0.5 mm sieve for chemical analyses. Eleven extractants covering various acids, bases and buffered solutions were used to test for K availability. Total K was extracted by HF-HClO₄ digestion method as outlined. A pot experiment was conducted with air-dried sample from each soil (1 kg/pot, 12cm x 15cm size). Polythylene film was used between soil and pot to avoid contamination from the earthen wire pots. Soils in each pot was kept submerged for 3 days for wetting. Four weeks old healthy rice seedlings (Oryza sativa cv. BR-4) were transplanted (4 seedlings/ pot). About 2-3 cm level of standing water was maintained throughout the whole experimental period. The experiment was arranged in a completely randomized block design with three replications. Plant sampling was carried at 60 and 90 days after transplanting, dried for 16 hours at 65°c (1°C) and ground to 1 mm size in a micro-grinder. Particle-size distribution was determined by hydrometer method. pH was measured with a combined glass/colomel electrode and that of organic C by wet oxidation method. CEG was estimated from N NH₄OAc (pH 7.0) extract. Potassium in soil and plant extracts was measured by flame photometer.

Source of Information: Sri Lankan Journal of Agricultural Science 25(2), 1988

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Summarizing the results obtained so far, the modified boiling 1N HNO₃ method was found to be the best of all the extractants. The measure of availability of a particular nutrient is best judged by the performance of crops under field experiments carried out under natural conditions. The laboratory index of availability, however, could be used as a prelude to field experiments and fertilizer trials since, "a chemical method can be taken to be a true index of the fertilizer needs of the soil only when it is correlated with crop yields and plant growth responses to fertilizers.

Knowledge Management: Journal