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Soil Fertility Status of Some of the Intensive Crop Growing Areas Under Major Agro-ecological Zones of Bangladesh

N. C. Shil
Principal Scientific Officer
Soil Science Division, Bangladesh Agricultural Research Institute (BARI), Gazipur

M. A. Saleque
Coordinator for Advanced Studies and Research
Bangladesh Rice Research Institute (BRRI), Gazipur

M. R. Islam
Professor
Soil Science Department, Bangladesh Agricultural University (BAU), Mymensingh, Bangladesh

M. Jahiruddin
Professor
Soil Science Department, Bangladesh Agricultural University (BAU), Mymensingh, Bangladesh.

Abstract/ Executive Summary:

Laboratory studies on soil fertility evaluation was carried out across major agro- ecological zones (AEZs) of Bangladesh to know the nutrient status of soils and to relate those with soil properties like pH, organic matter, CEC, and clay content. Thirty five composite soil samples were collected from intensive crop growing sites, which covered 17 AEZs of Bangladesh. After proper processing, the samples were analyzed for texture, pH, organic carbon, CEC, exchangeable cations (K, Ca, Mg and Na), total N, available P and S following standard methods. The textural class of the soils collected from AEZ 12 and 13 appeared to be mostly clay. Clay loam soil was found in AEZ 4, 8, 9, 11, 25 and 28. Loamy soil was seen in AEZ 1 while AEZ 22, 23 and 29 were mostly sandy textured. The results revealed that 65.7% of the tested soil was acidic while 25.7% was alkaline in nature. All the tested soils showed lower pHKCl compared to pHH2O thus possessed negative charge. About 68.6% of the collected soils contained low (1.10-1.70%) level of organic matter, 25.7% soils retained it at medium level (1.71-2.40) and 5.7% soils at very low level (<1.0%). All the tested soils appeared to be deficient (< 0.12%) in nitrogen content. 68.6% soil samples had the low level of available P while only 8.6% retained it an optimum amount. About 80% of the tested soils contained low level of available S (7.9-14.7 mg kg -1) although coastal regions soils hold higher amount of available S. High CEC (20-38 cmol kg-1) was found in clay rich soils of AEZ 10, 11, 12, and 13. Study revealed that 40% of the collected soils were very low, 31.4% were low, 8.6% each of medium and optimum, and 11.4% contained high level of exchangeable K. The calcareous soils (AEZ 10, 11, 12 and 13) contained very high level of Ca. Non calcareous soils also showed fairly good level of Ca content except AEZ 1, 3, 23 and 29. Sandy textured soils of greater Dinajpur, Rangpur, Moulvibazar showed lower level of exchangeable Mg. About 86% of the tested soils had the lower (< 2%) potassium saturation percentage (KSP), which needs K application for sustainable crop production. Estimate showed that 44% variability for CEC may be attributed by clay content and the relationship was significant (p = 0.05). Again, 50.4 and 65.6% variability in exchangeable K and Mg, respectively may be governed by clay content of the soils, while such relationship for Ca was non-significant. CEC may contribute 62.2, 92.3 and 83.9% variability for exchangeable K, Ca and Mg content in soils, respectively. The fertility status of most of the studied soils (except AEZ 10, 12, 13 and to some extent 11) appeared to be low to very low, which demand judicious management in order to achieve food security and to conserve the soil fertility.

Keywords: Soil fertility, Agro-ecological zones, Texture, Organic matter, Cation exchange capacity

Location: 21 districts and 17 AEZs of Bangladesh

Start Date: 00-02-2009

End Date: 00-04-2009

Program Area: Resource Development and Management

Commodity: Fertilizer

Objectives:

The present studies were undertaken across major agro-ecological zones (AEZs) of Bangladesh in order to know the nutrient status of soils and to relate those with soil properties like pH, organic matter, CEC, exchangeable bases and clay content.

Methodology:

Sites: Soil collection sites were selected mostly on the basis of the cropping intensity of the region covering major agro ecological zones (AEZs) of Bangladesh.
Soils: The collected soils represented 19 series, which covered 21 districts and 17 AEZs of Bangladesh.
Collection, preparation and analysis of soils: Five soil samples (0-15 cm) were collected from each of the selected sites and mixed together thoroughly to make a composite sample. Soils were mostly collected from farmers’ field to get the representative sample of the locality during February - April 2009. Collected composite soil samples (35) were brought to the Soil Science Laboratory, BARI, Gazipur and air dried and ground to pass through 20 mesh sieve. The samples were then analyzed for texture, pH, organic carbon, CEC, exchangeable cations (K, Ca, Mg, Na), total N, available P and available S following standard laboratory methods as stated below.
Analytical methods: Mechanical analysis of soils was done by hydrometer method (Bouyoucos, 1962) and the textural class was determined from Marshall’s triangular co-ordinate following USDA system. A glass electrode pH meter calibrated with buffer pH 7.0 and 4.0 measured the pH of the soil suspension maintaining soil: water ratio of 1:2.5 (Page et al., 1982). The pHKCl was determined by stirring 10 g soil in 25 ml of 1.0 M KCl solution in a similar manner of pHH2O determination. The difference between the pH in KCl and that in water gave the value of Δ pH.
Δ pH = pHKCl - pHH2O
The value of the Δ pH indicates the surface charge characteristics. A positive value of Δ pH symbolizes positive surface charge while the negative value denotes negative surface charge. Cation exchange capacity of the soil was determined by Schollenberger (1980) method. Organic carbon was determined by wet oxidation method as described by Walkley and Black (1935) and the organic matter content was estimated by multiplying the percent organic carbon with the Van Bemmelen factor 1.73. Total N content of soil was determined following micro Kjeldhal method (Bremmer and Mulvancy, 1982). For the determination of available P, Bray 1 method (Bray and Kurtz, 1945) was used for acid soils while Olsen method (Olsen, 1982) was followed for neutral and alkaline soils. The filtrate was analyzed for P following Murphy and Riley (1962) method. Available S was determined by extracting the soil sample with 0.15 % CaCl₂ solution as described by Page et al. (1982). The reading was taken using UV visible Spectrophotometer (Varian Model 50 Conc.) at 720 nm and 420 nm wavelength for P and S, respectively. Exchangeable bases (K, Ca, Mg and Na) were extracted with 1 M NH4OAc solution (pH = 7) (Thomas, 1982). In case of exchangeable K, the reading was taken directly using AAS (Chemito AA 203) at 766.5 nm wavelength. For Ca, 2 ml aliquot was diluted with 1 ml of La2O3 and 7 ml of distilled water and then reading was taken using AAS (Chemito AA 203). In case Mg and Na, 1 ml aliquot was diluted with 9 ml of distilled water and reading was taken using the same AAS.
Statistical analysis: The data were statistically analyzed for mean, range, standard deviation, standard error following the methods of descriptive statistics. Regression analysis was also done to observe the relationship between desired soil properties.

Source of Information: Bangladesh J. Agril. Res. 41(4): 735-757, December 2016 ISSN 0258-7122 (Print), 2408-8293 (Online)

Article Link (Online Journal):

Funding Source:

Budget:

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Achievement/Findings:

Studied soils varied widely in texture, pH, CEC, organic matter and essential plant nutrient elements. Sand dominated loamy textured soils were found in northern region while soils of north eastern and south eastern part except coastal belt was mostly sandy textured. The middle part of the country was dominated by clay loam soil. The soils of south-western coastal belt appeared to be clay textured. The majority of the tested soils found to be acidic in nature. Organic matter status appeared to be remarkably low. Nitrogen deficiency was found in all soils. Available P and S contents were mostly low. Exchangeable K content was low to very low except clay rich soils of Ganges floodplain and Ganges tidal floodplain regions. The calcareous soils contained very high level of Ca. But non calcareous soils also retained fairly good level of exchangeable Ca except sandy textured ones. Magnesium deficiency was found in sandy textured soils but rest of the soils hold optimum to high level of exchangeable Mg. Thus the fertility status of most of the Bangladesh soils (except AEZ 10, 12, 13 and to some extent 11) appeared to be low to very low, which demand judicious management in order to achieve food security and to maintain the soil fertility.

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