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Soil Qualities of Saline and Non-saline Deltas of Bangladesh

M A Saleque
Bangladesh Rice Research Institute Regional Station, Barisal 8200, Bangladesh.

M N H Mahmud
Bangladesh Rice Research Institute Regional Station, Barisal 8200, Bangladesh.

A Khatun
Bangladesh Rice Research Institute Regional Station, Barisal 8200, Bangladesh.

M M Haque
Soil Science Division, Bangladesh Rice Research Institute, Gazipur 1701, Bangladesh.

A T M S Hossain
Soil Science Division, Bangladesh Rice Research Institute, Gazipur 1701, Bangladesh.

S K Zaman
Soil Science Division, Bangladesh Rice Research Institute, Gazipur 1701, Bangladesh.

Abstract/ Executive Summary:

Delta soils, containing relatively more carbon, N, P and K than upland soils play an important role in carbon sequestration and mitigation of global warming. We, therefore, investigated different fractions of organic carbon content in 32 saline and non-saline delta soils from the Barisal region along with some chemical properties. Electrical conductivity in the saturation cxtract of the topsoil varied from 0.48 to 13.1 ds/m in December. The soil pH ranged from 4.64 to 7.63 and soil organic matter from 0.74 to 1.96%. Mineralizble carbon (C_min) varied from 0.15 to 0.32 g/kg and potassium permanganate oxidizable C (C_PM) 986 to 1195 ppm. Fractionation of organic carbon showed that the range of very labile C fraction was 0.32-1.52%, labile C fraction varied from 0.07-1.68% and less labile fraction was in the range of 0.04-1.17%. The tested soils had a wide range of available P (2-13 mg/kg) and available K varied from 0.18 to as high as 0.81 cmol kg^-1 soil. Across the soils, the K saturation was 1.01-3.75% of the basic cations. The soil analysis indicated mild Zn deficiency in the coastal delta soils with a pH above 7.0. Estimated nutrient supplying capacities according to the quantitative evaluation of fertility of tropical soil (QUEFTS) model is 42-163 kg N, 6- 23 kg P and 33-447 kg K/ha. Many of the tested soils showed ability to support 5 t/ha yield without any N, P and K fertilizers, while some others would require fertilization. Given the fact of higher proportion of labile C, delta soils need attention for carbon sequestration to reverse global warming. The notion of higher fertility in delta soils seems to be reinvestigated and site-specific nutrient management need to be done for sustainable rice yields in the coastal region.

Keywords: Carbon fractions, Delta soils, Rice, Salinity, Soil-test bas cd fertilizer recommendation.

Location: Barisal, Jhalokathi, Pirojpur, Borguna, Patuakhali and Bhola districts

Start Date: 00-12-2007

End Date: 00-04-2008

Program Area: Risk Management in Agriculture

Commodity: Soil salinity

Objectives:

To describe general features of coastal delta soils in Bangladesh and explore some options for improved organic matter and fertilizer management for rice in these regions that can contribute to the carbon sequestration and curve climate change.

Methodology:

Soil samples were collected from farmers' fields of Barisal, Jhalokathi, Pirojpur, Borguna, Patuakhali and Bhola districts in December 2007-April 2008. Sampling sites were located between 4 to 76 km away from the sea, but all of them were tidal flooded seasonally. Dominant cropping patterns at the sampling sites were either Rice-Rice-Fallow or Rice-Fallow-Fallow. At each site, 9 soil samples were collected and composited from the rice root zone (0 -15 cm depth). SoiI samples were dried, crushed and sieved through a 2 mm sieve. Samples were analyzed for electrical conductivity from saturation paste water pH (1:2 soil: water), Walkley and Black organic carbon, potassium permanganate extractable organic carbon, organic carbon fractions. Carbon dioxide emission was measure as index of mineralizable C. Available P was extracted with 0.5 M NaHCO₃(pH 8.5) exchangeable K extracted by 1.0 N neutral ammonium acetate, and available Zn by 0.1 N HCI. Each sample was analyzed in duplicate. Potential N, P and K supplying capacities were estimated following QUEFTS model

SN= 0.25 (pH-3) x6.8 x organic C x 10 ------- (1)

SP= (1-0.50 (pH-6)²) x (0.35 x organic C x10 x1.5 (Olsen P) ................ (2)

SK= (0.625 (3.4-0.4pH) x 1350 x exchK x10) /(2+0.9xorg.C)..............(3)

SN, SP and K stands for potential supply of N, P and K pH is applicable in the range of 4.5-7.0, organic C is expressed as %, Olsen P as mg/kg and exchangeable K in coml/kg. Factor 1.5 instead of 0.5 for Olsen P and 1350 instead of 400 for exchangeable K ws modified to adjust P and K supply for lowland rice soils.

Source of Information: Bangladesh Rice J. 14 (I & 2): 99-111, 2009

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Improved fertilizer recommendations for modern rice varieties grown in the delta soils of Bangladesh are urgently needed not only for increasing yield but also for C sequestration. They should be based on more detailed background studies of soil characteristics and fertilizer response trials for rice- based cropping systems In this region. Recommendations developed could be based on soil testing but probably would need to combine different concepts Ior the interpretation of soiI test values. Integrating these different elements could then contribute to increase rice production in delta soils and improve the livelihoods of poor farmers in the region. Soil C sequestration through improved nutrient management practices has the potential to offset CO₂ emissions as well as food security of the poor farmers in the coastal region.

Knowledge Management: Journal