Agricultural Research Management Information System

Home
Research Summary
Search
About Us
- ARMIS
- Brochure
Contact Us
Report
User Request
Data Input
Help
- Operation Manual
  - PDF
  - Video
- Program Area & Commodity
We have reached 37600 number of research entries at this moment.

- Logout

Research Detail

Home
Research
Detail

Comparative Performance of Two Extractants in Colorimetric Determination of Soil Organic Matter in Paddy Soil

Md. Asaduzzaman
Department of Soil Science, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh

Mohammed Abdul Kader
Department of Soil Science, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh; School of Agriculture and Food Technology, University of South Pacific, Samoa; School of Veterinary and Life Sciences, Murdoch University, Murdoch, 6150 Australia.

Shamim Ara Begum
On-Farm Research Division, Bangladesh Agricultural Research Institute, Mymensingh 2202, Bangladesh.

M. A. Islam
Department of Soil Science, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh

Abstract/ Executive Summary:

Commonly used soil organic carbon (SOC) determination methods are expensive, time consuming, require equipment and skilled personnel making them impractical to use at field level. Therefore, a laboratory analytical study was carried out to identify a suitable extractant for SOC extraction as part of an ongoing effort to develop a low cost quick method for determining soil organic matter (SOM) at field level. For this purpose, 38 soil samples were collected from different Agro Ecological Zone (AEZ) to represent typical rice based cropping pattern covering a sufficient range in texture, soil organic matter, pH, and type of management. Two extractants e.g. NaOH-Pyrophosphate + HCl and NaOH-EDTA were used to extract organic carbon from soil and two wavelength e.g. 300 and 400 nm were used to measure the absorbance of organic carbon in spectrophotometer. Soil organic carbon measurements by CNS analyzer were used as reference measurement to compare the extracting efficiency of SOC by the selected extractants. Both the extract and wavelength showed different degrees of error in OC measurement. The error sum square of NaOH-Pyrophosphate + HCl and NaOH-EDTA measured at 300 nm wavelength were 15.21 and 13.35 whereas at 400 nm it was 227.37 and 19.95, respectively. Consequently, the average error percentages at 300 nm were -33 and -8 while at 400 nm it was - 187 and -16. Based on the error sum square and error percentage, NaOH-Pyrophosphate + HCl performed better than the NaOH-EDTA, and 400 nm wavelength came out better than the 300 nm wavelength. In addition, both the extracts produced coloured solutions which were easily visible or detectable by naked eye and the colour intensity increased with the increase in SOC content. Variations in colour among the soils depending on organic matter content indicate that it would be possible to develop a new low cost method for SOM determination at field level by using NaOH-Pyrophosphate + HCl as the extractant. Further research is warranted to confirm this finding.

Keywords: Soil organic matter, Colorimetric determination, Extractants, Low cost method, Rice

Location: Soil Resources Development Institute (SRDI)

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Soil Health

Objectives:

To identify a suitable extractant for SOC extraction as part of an ongoing effort to develop a low cost quick method for determining soil organic matter (SOM) at field level.

Methodology:

Soils In total a set of 38 soils (top 15cm) were collected from farmers' fields to represent majority of the typical rice based cropping patterns in Bangladesh covering different combinations of soil terrain types (e.g. non calcareous floodplain soil, calcareous floodplain soil, terrace soil, etc.) and land types. Among them 25 soils were earlier described by Kader et al, 2015. Fifteen sub soil samples from a whole field in each location were collected by means of an auger (Ø 2.5 cm) and these samples were bulked and left to dry in air. Prior to the physico-chemical analysis of the soil samples, the air dried soils were broken apart and crushed by hand to pass through a 2-mm sieve. Soil series of the collected soil samples were identified in most of the cases, with the help of expert personnel of Soil Resources Development Institute (SRDI). Name of the soil series along with locations, land type and cropping patterns are presented. General soil properties Mechanical analysis of soil was done by hydrometer method (Buoyoucos, 1926) and the textural class was determined following “Marshall’s Triangular Coordinates” using USDA system. The pH_KCl of air-dried soil samples was measured in 1M KCl (1:2.5 soil weight (g): extractant volume (ml)) suspension using a glass electrode. Total N content in soil was determined by Kjeldahl method (Bremner and Mulvaney, 1982). Soil organic carbon (SOC) determined by Varimax CNS analyser (Elementar Analysesysteme, Germany) and Simudzu TOC analyser were used as the reference measure of SOC. Soil samples having no carbonate were analysed with a Variomax CNS-analyzer on 800 mg sub-samples. Carbonate containing soils were analysed using a Shimadzu TOC analyzer with a ‘SSM-5000A’ module for solid samples and feeded into the ‘TOC-VCPN’ which determined subsequently the organic carbon contents. The organic carbon concentration was calculated as the difference between the total carbon and the inorganic carbon concentration. The experiments were geared toward identifying a suitable extractant for SOC quantification. Two extractants on the extraction of SOC were evaluated at a soil/extractant ratio of 1:200. The extractants tested were 0.25 mol L⁻¹ NaOH + 0.05 mol L⁻¹ EDTA (after Bowman et al., 1991, Harvey et al, 2009), and 0.25 mol L⁻¹ NaOH + 0.1 mol L⁻¹ Na₄P₂O₇.10H₂O (pyrophosphate) followed by 1 mol L⁻¹ HCl (after Schnitzer, 1982). NaOH was chosen for its ability to extract particulate SOM (unprotected SOM pool) while EDTA was used to bind Fe & Al and Na₄P₂O₇.10H₂O were chosen for its ability to extract mineral bound SOM pool. An amount of 0.1g of airdried soil was weighed into a 50-mL polypropylene centrifuge tube followed by addition of 20 mL of NaOH-pyrophosphate extractant solution and shaken by hand for 15 to 20 s at 1-min intervals for 5 min. The extract was filtrated through 0.45 µm polycarbonate syringe filters. The absorbance of the filtrate was measured at 300 nm and 400 nm with a UV-Vis spectrophotometer (Spectronic GENESYS 5 UV-Vis Spectrophotometer, USA) with a path length of 1 cm. A calibration curve was prepared by using absorbance and SOC content of the selected soil samples (developed using Beer’s law and soils of known SOC content) to determine SOC content of all unknown soil samples based on measured absorbance. It was a visual observation. The soils were sub grouped into four groups based on the BARC (2005) soil organic matter classification. According to this classification, soil containing >1, 1-1.7, 1.8- 3.5 and <3.5% organic matter were classified as very low, low, medium and high organic matter content soil. Based on the visual observation of the extract colour the extracts were then classified in to the above mentioned four groups. Statistical Analysis- Correlation analysis was used to investigate the relation among soil properties in SPSS service pack 19 (SPSS Lnc, USA). Mean comparison of the sum squares of errors and percentage of errors were also made in SPSS by means of one way ANOVA followed by Dunkan’s Multiple Range Test (DMRT).

Source of Information: Journal of South Pacific Agriculture, Volume 20, 2017

Article Link (Online Journal):

Funding Source:

1.

Budget:

Total Budget (Tk.) :

Achievement/Findings:

NaOH-Pyrophosphate + HCl extract with 400 nm wavelength performed better for determination of soil organic carbon as compare to NaOH-EDTA extract. This extract also preferred to be better than NaOH-EDTA as it seemed to produce intense colour. Intensity of the colour increased with the increase of SOC indicate the potentiality of NaOH-Pyrophosphate + HCl as an extractant to develop a new low cost method for SOM determination at field level. However, further research is needed with fine tuning to finally recommend this extractant as the essential part of the expected low cost method for determination of soil organic matter.

Knowledge Management: Journal