Variations in soil organic carbon content with chronosequence, soil depth and aggregate size under shifting cultivation

Sabina Yasmin Laskar; Gudeta Weldesemayat Sileshi; Karabi Pathak; Nirmal Debnath; Arun Jyoti Nath; Kaynath Yasmin Laskar; Pator Singnar; Ashesh Kumar Das

doi:10.1016/j.scitotenv.2020.143114

Variations in soil organic carbon content with chronosequence, soil depth and aggregate size under shifting cultivation

Sci Total Environ. 2021 Mar 25:762:143114. doi: 10.1016/j.scitotenv.2020.143114. Epub 2020 Oct 21.

Authors

Sabina Yasmin Laskar¹, Gudeta Weldesemayat Sileshi², Karabi Pathak³, Nirmal Debnath¹, Arun Jyoti Nath⁴, Kaynath Yasmin Laskar¹, Pator Singnar¹, Ashesh Kumar Das¹

Affiliations

¹ Department of Ecology and Environmental Science, Assam University, Silchar 788011, Assam, India.
² Department of Plant Biology and Biodiversity Management, Addis Ababa University, Addis Ababa, Ethiopia; University of KwaZulu-Natal, Private Bag X01, Pietermaritzburg 3209, South Africa.
³ Department of Ecology and Environmental Science, Assam University, Silchar 788011, Assam, India; Carbon Management and Sequestration Center, The Ohio State University, Columbus, OH 43210, USA.
⁴ Department of Ecology and Environmental Science, Assam University, Silchar 788011, Assam, India. Electronic address: arunjyotinath@gmail.com.

PMID: 33129519
DOI: 10.1016/j.scitotenv.2020.143114

Abstract

Shifting cultivation is a globally important form of agriculture covering over 280 million hectares in the tropics, but it has often been blamed for deforestation and forest degradation. In North East India (NEI) it has been practiced for millennia and it is an important element of the cultural identity of indigenous communities. It is often practiced on slopping lands with fragile soils (mostly Acrisols), which are prone to rapid degradation with cultivation. The shortened fallow cycle as practised currently is ecologically unsustainable and economically not viable. This study aimed to quantify (i) changes in soil bulk density, aggregate stability and compaction in relation to chronosequence and soil depth, (ii) changes in the proportion of macro, meso, and micro aggregates and associated soil organic carbon (SOC) content in relation to soil depth and fallow chronosequence, and (iii) determine the minimum fallow length that achieves SOC stocks comparable with adjacent intact forest land. The proportion of soil macro-aggregates and meso-aggregates significantly varied with land-use and soil depth as well as their interactive effects. Across all soil depths, forest land had the highest proportion of macro-aggregates (75.6%), while the currently cultivated land had the least proportion (51.1%). The SOC contents in macro-aggregates increased with fallow age and decreased with soil depth; the highest (1.95%) being in the top 10 cm soil of 20 years old fallows and the lowest (0.39%) in 21-30 cm depth of 5 years old fallows. Multivariate analysis identified bulk density and porosity as the most important variables to discriminate between land use practices. The analysis provided evidence for significant changes in soil compaction, aggregate stability and SOC content with the transition from undisturbed forest to slash-and-burn cultivation and fallow phases. It is concluded that a minimum of 20 years of fallow period is required to achieve SOC content and C stocks comparable with intact forest land.

Keywords: Acrisols; Aggregate stability; Fallow land; Forest degradation; Slash-and-burn.