Soil organic matter in biogenic, intermediate and physicogenic aggregates under agroecological management

ABSTRACT Agroecological management can favor the improvement of soil attributes, especially soil organic matter (SOM) and soil aggregation. The objective of the study was to quantify the carbon contents of the humic and oxidizable fractions of SOM of aggregates from different origins from agroecological management systems. Five experimental areas located in the Integrated Agroecological Production System were evaluated: AFS – Agroforestry System; C-SUN – Coffee in full sun; C-SHA – Shaded coffee; AL-FLE – Cultivation in alleys of Flemingia macrophylla with green beans; and NT – No-tillage. The aggregates were separated, identified, and classified as to their origin or formation pathways into biogenic, intermediate, and physicogenic. The carbon contents of the humic fractions fulvic acid (C-FAF), humic acid (C-HAF) and humin (C-HUMF); and oxidizable fractions (F1 and F2, labile; and F3 and F4, recalcitrant) of SOM were determined. The greatest variations in the carbon values of the humic fractions were observed in the aggregates of the AFS, C-SUN and C-SHA systems. In relation to C-HUMF, the highest contents of this fraction were quantified in the biogenic and intermediate aggregates of the C-SUN, C-SHA and AL-FLE systems. The carbon contents of the oxidizable fractions of SOM showed variability between the management systems, mainly for the F1, F2 and F3 fractions in the aggregates under C-SUN and C-SHA. The C-SUN system showed a higher proportion of more humified and recalcitrant fractions of SOM when compared to the C-SHA system. The management practices maids in the agroecological systems of C-SHA, C-SUN and AFS promoted improvements in soil quality.摘要：农业生态管理可有效改善土壤属性，尤以土壤有机质（soil organic matter, SOM）与土壤团聚体（soil aggregation）为著。本研究旨在量化不同农业生态管理系统来源团聚体中SOM的腐殖质组分与可氧化组分的碳含量。本研究对综合农业生态生产系统内的5个试验区域进行了评估，分别为：农林业系统（AFS – Agroforestry System）、全日照咖啡种植园（C-SUN – Coffee in full sun）、遮阴咖啡种植园（C-SHA – Shaded coffee）、大叶千斤拔（Flemingia macrophylla）条带间作绿豆种植模式（AL-FLE – Cultivation in alleys of Flemingia macrophylla with green beans）以及免耕系统（NT – No-tillage）。研究人员对团聚体进行分离、鉴定，并依据其来源与形成路径划分为生物成因、中间成因及物理成因三类。随后测定了SOM的腐殖质组分碳含量：富里酸（C-FAF, fulvic acid）、胡敏酸（C-HAF, humic acid）与胡敏素（C-HUMF, humin）的碳含量，以及可氧化组分碳含量：易分解组分F1、F2与难分解组分F3、F4。研究结果表明，腐殖质组分碳含量的最大波动见于AFS、C-SUN与C-SHA系统的团聚体中。就胡敏素碳（C-HUMF）而言，其最高含量出现在C-SUN、C-SHA与AL-FLE系统的生物成因及中间成因团聚体内。SOM可氧化组分的碳含量在不同管理系统间存在显著差异，其中C-SUN与C-SHA系统团聚体的F1、F2及F3组分差异尤为突出。相较于C-SHA系统，C-SUN系统的SOM腐殖化程度更高，难分解组分占比更大。C-SHA、C-SUN与AFS农业生态系统的管理措施可有效改善土壤质量。