Abstract
Land use change and cropping patterns are important factors for controlling carbon sequestration in soils and they may also change the relative importance of different mechanisms of soil organic matter stabilization. The study was conducted to investigate the state of carbon sequestration in soil aggregates under different cropping patterns of Khulna, Jessore and Chapainawabganj districts in Bangladesh. Thirty-six soil samples were collected from (0 - 100 cm depth) above mentioned regions of three physiographic regions: Ganges Meander Floodplain, Ganges Tidal Floodplain and High Barind Tract. The texture of the samples varied within three soil texture groups, Silt Loam, Silty Clay Loam and Silty Clay. The highest NSI value (0.89) was found under Wheat-Fallow-T. Aman cropping pattern in Silty Clay soils (sample No 15) and lowest value (0.59) was found Vegetables/Mustard-Fallow-T. Aman cropping pattern in Silt Loam soils (sample No 17). The highest value (735.20 mg•kg−1) of active C was observed under Chickpea/mustard-T. Aman (Sample No 31) and the lowest value (619.23 mg•kg−1) was found in case of Wheat-Fallow-T. Aman cropping pattern (Sample No 30). The highest SOC stock (1.62 Kg C m−2) was found in Silty Clay Loam soil under Mungbean/Ash gourd-T. Aman cropping pattern (Sample no 4) and the lowest SOC stock (0.35 Kg C m−2) was found in Silt Loam soil under Cauliflower/Pumkin/Spinach-T. Aman Cropping pattern (Sample No 2). Soil organic carbon associated with different size aggregates was the highest (3.14%) under Mungbean/Ash gourd-T. Aman (Sample No 20) and was the lowest (0.36%) under Cauliflower/Pumkin/Spinach-T. Aman cropping pattern (Sample No 2). Organic carbon content in aggregate size ranges > 2000 μm (SOC1), 2000 - 250 μm (SOC2), 250-53 μm (SOC3), and 2000 μm, 2000 - 250 μm and 250 - 53 μm, aggregates. Significant positive correlations were found between SOC stock and SOC1, SOC stock and SOC2, SOC stock and SOC3, SOC stock and SOC4.
Highlights
Global warming is a major threat to the environment and soil management practices are believed to contribute significantly to changing environmental conditions [1]
Soil surface layers account for the main part of the soil carbon stocks: on average, the 47% of the carbon stored in soils is held in the first 30 cm; about 2/3 are stored within a depth of 50 cm and the 80% within one meter
In this research we found that the Normalized Stability Index (NSI) varied from 0.51 to 0.89 under different cropping patterns (Appendix Table A1)
Summary
Global warming is a major threat to the environment and soil management practices are believed to contribute significantly to changing environmental conditions [1]. Tillage causes loss of soil organic matter through destruction of macro-aggregates and microbial mineralization of the physically protected SOM pool. Rice-wheat surface soils (0 - 15 or 0 - 20 cm) from Bangladesh increase in SOC as their silt + clay fraction increases This variability may reflect differences in manure use, years under cultivation, tillage, sampling depth or length of time that soils are flooded [9]. Low external input of organic amendment causes depletion of SOC pool because nutrients harvested in agricultural products are not replaced, and are made available through mineralization of SOM. In loam soils highest %SOM was obtained under Rabi-Jute-Turmeric (1.54%) and lowest under Boro-Fallow-T. The objectives of the research project were to evaluate the state of SOC sequestration in the agricultural soils under different cropping patterns and estimate the carbon stock of soils
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