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Carbon Sequestration in Soil Aggregates Under Different Cropping Pattern in Ganges Meander and Ganges Tidal Floodplains of Khulna Region

S.M.F. Rabbi
Soil Science Discipline, Khulna University, Khulna 9208, Bangladesh

M.S. Amin
Soil Science Discipline, Khulna University, Khulna 9208, Bangladesh

K. Rezoa
Soil Science Discipline, Khulna University, Khulna 9208, Bangladesh

M. Hanif*
Soil Science Discipline, Khulna University, Khulna 9208, Bangladesh

Abstract/ Executive Summary:

Sequestering carbon in soil aggregates is a long term solution to global warming that will keep CO2 out of the atmosphere. The study was conducted to investigate the state of carbon sequestration in soil aggregates under different cropping patterns of Khulna region. Twelve different cropping patterns were selected. Soil particle size distribution, microaggregate analysis, aggregate stability, normalized stability index (NSI) and organic carbon were determined. The soil organic carbon (SOC) associated with aggregate size ranges (8-2, 2-0.25 and 0.25-0.05 mm) were separated and determined. The SOC associated with 2-0.25 mm aggregates was generally higher than SOC associated with 8-2 mm and 0.25-0.05 mm aggregates. The state of aggregation (7.5%) and degree of aggregation (13.04%) were found high under Til (Sesame)-FallowT.aman cropping pattern and low under Aus-Fallow-Vegetable/ Vegetable-Sugarcane cropping pattern. The dispersion factor (28.25%) was highest under Vegetable cropping pattern. The highest NSI value (0.95) was under Fallow-Fallow-T.aman cropping pattern at Dhulirhat union in Satkhira district and the lowest value (0.29) was under Fallow-Fallow-T.aman cropping pattern at Aatlia union in Khulna district. The highest organic carbon content in aggregate size ranging from 8-2, 2-0.25 and 0.25-0.05 mm was found 2.28, 3.00 and 2.63%, respectively under Fallow-Fallow-T.aman cropping pattern at Dhulirhat union in Satkhira district. The lowest organic carbon content was found 0.53, 0.58 and 0.51%, respectively under BoroFallow-T.aman cropping pattern at Sokhipur union in Satkhira district. Organic carbon associated with 8-2 mm and 0.25-0.05 mm aggregate was negatively correlated with sand and positively with clay contents of the soils. Carbon associated with different aggregates was also positively correlated.

Keywords: Carbon sequestration, Cropping pattern, Soil aggregates

Location: Ganges Meander and Ganges Tidal Floodplains of Khulna region

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Carbon sequestration

Objectives:

Conventional tillage is a common tillage practice in Bangladesh which may cause aggregate disruption and rapid carbon emission. The cropping intensity also is high in Bangladesh due to high population density. This may increase organic matter loss from soil. So, the objective of the research work was to determine the state of carbon sequestration retention in soil aggregates.

Methodology:

Top soil (0-6 cm) samples were collected from different locations of agricultural fields under different cropping pattern and conventional tillage practices in the Ganges Meander and Ganges Tidal Floodplains of Khulna region. Soil samples were collected on the basis of composite sampling method as suggested by the Soil Survey Staff of the USDA (1951) and then processed for subsequent analyses.

Particle size analysis was carried out by combination of sieving and hydrometer method (Gee and Bauder, 1986). Textural class was determined by Marshall’s Triangular co-ordinate system. Soil structure was evaluated by microaggregate analysis of the soils following the method Kachinskii (1965). The state of aggregation, degree of aggregation and dispersion factor was determined by using the following equations (Baver and Rhoades, 1932).

State of aggregation = a - b

Degree of aggregation = a - b / 100- b x 100

Dispersion factor = x / y x 100

Where a = percentage of aggregates larger than a specified size in microaggregate analysis, b = percentage of particles larger than a specified size in particle size analysis, x = percentage of clay in microaggregate analysis and y = percentage of clay in particle size analysis.

For determination of soil organic carbon (SOC) associated with soil aggregates of 8-2 mm, 2- 0.25 mm and 0.25-0.05 mm size ranges were kept submerged with distilled water for 5 minutes and then separated manually by moving the sieve 3 cm up and down under water with 50 repetitions during a period of 2 minutes. Soil samples of these three fractions were then oven dried at 70⁰C for 24 hours. The carbon content of each size fractions were determined by the method as described by Tyurin (1936).

For determination of aggregate stability, soils were divided into 8-2 mm, 2-0.25 mm and 0.25- 0.05 mm size fractions by using mechanical shaker. For wet sieving with slaking pretreatment 10 g air dry soil samples from each aggregate size fraction were submerged for 5 minutes and then separated manually by moving the sieve 3 cm up and down under water with 50 repetitions during a period of 2 minutes. For wet sieving with wetted pretreatment the air dried samples were adjusted to field capacity by soaking with water for overnight before submerging in water. The soils were then sieved for 2 minutes by the method as stated before. Soil samples of these three fractions were then oven dried at 105⁰C for 24 hours. Primary particles retained on the sieves were determined by sieving and then oven dried at 105⁰C for 24 hours. The normalized stability index (NSI) of aggregates was calculated by the following formula (Six et al., 2000). NSI = 1- [DL/DL (max)].

Source of Information: Khulna University Studies Special Issue (SESB 2010): 21-29 : June, 2010

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Soils under Fallow-Fallow-T.aman cropping pattern had higher NSI and SOC. The cultivation of rice in boro and Kharif-2 season decreased NSI of soils. The percentage of SOC associated with 2-0.25 and 0.25-0.05 mm aggregates increased with increasing clay contents of the investigated soils. Soil organic matter can be physically stabilized or protected from decomposition, through microaggregation, or intimate association with silt and clay particles. Hence, soil aggregation is an important process of C sequestration. Aggregate stability and cropping pattern are strongly correlated with soil carbon sequestration.

Knowledge Management: Journal