Laskar Sabina Yasmin, Sileshi Gudeta Weldesemayat, Pathak Karabi, Debnath Nirmal, Nath Arun Jyoti, Laskar Kaynath Yasmin, Singnar Pator, Das Ashesh Kumar
Department of Ecology and Environmental Science, Assam University, Silchar 788011, Assam, India.
Department of Plant Biology and Biodiversity Management, Addis Ababa University, Addis Ababa, Ethiopia; University of KwaZulu-Natal, Private Bag X01, Pietermaritzburg 3209, South Africa.
Sci Total Environ. 2021 Mar 25;762:143114. doi: 10.1016/j.scitotenv.2020.143114. Epub 2020 Oct 21.
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.
轮垦是一种在全球范围内具有重要意义的农业形式，在热带地区覆盖面积超过2.8亿公顷，但它常常被指责导致森林砍伐和森林退化。在印度东北部（NEI），这种耕种方式已经延续了数千年，并且是当地土著社区文化身份的一个重要元素。它通常在土壤脆弱（主要是强淋溶土）的坡地上进行，这种土壤在耕种时容易迅速退化。目前实行的缩短休耕周期在生态上是不可持续的，在经济上也是不可行的。本研究旨在量化：（i）与时间序列和土壤深度相关的土壤容重、团聚体稳定性和压实度的变化；（ii）与土壤深度和休耕时间序列相关的大、中、微团聚体比例变化以及相关土壤有机碳（SOC）含量变化；（iii）确定能够实现与相邻完整林地相当的SOC储量所需的最短休耕时长。土壤大团聚体和中团聚体的比例随土地利用方式、土壤深度及其交互作用而显著变化。在所有土壤深度中，林地的大团聚体比例最高（75.6%），而目前的耕地比例最低（51.1%）。大团聚体中的SOC含量随休耕年限增加而增加，随土壤深度增加而减少；最高含量（1.95%）出现在20年休耕期的表层10厘米土壤中，最低含量（0.39%）出现在5年休耕期的21 - 30厘米深度土壤中。多变量分析确定容重和孔隙度是区分土地利用方式的最重要变量。该分析提供了证据，表明随着从未受干扰的森林向刀耕火种耕种和休耕阶段的转变，土壤压实度、团聚体稳定性和SOC含量发生了显著变化。研究得出结论，至少需要20年的休耕期才能实现与完整林地相当的SOC含量和碳储量。
