Dynamics of newly formed humic acid and fulvic acid in aggregates after addition of the 14C-labelled wheat straw in a typic hapludoll of Northeast China

Abstract

This research chose the Typic Hapludoll in the northeast of China and studied dynamics of newly formed humic acid (HA) and fulvic acid (FA) in aggregates after addition of the 14C-labelled wheat residues for 60, 180, and 360 days incubation using the aggregate classification combined with chemistry grouping of humic substances. Based on 14C isotope tracer technology, the results showed that the sorting selection of >2,000-μm and 2,000-250-μm macroaggregates on newly formed 14C-HA and 14C-FA was higher than microaggregates. In the >2,000-μm and 2,000-250-μm macroaggregates, the 14C-HA/14C-FA ratio decreased with the increase of incubation time and the formation of 14C-FA was faster than 14C-HA, which humic substance formation supported lignin theory of Waksman. In the <53-μm silt and clay components, 14C-HA/14C-FA ratio increased with the increase of incubation days and the formation of 14C-HA was faster than 14C-FA, indicating that the formation of humic substances followed the polyphenol theory of Kononova. In conclusion, organic fertilization would facilitate the formation of macroaggregates and thereby result in an enhanced accumulation of humic substances in macroaggregates. Therefore, with more potential of carbon sequestration, the >2,000-μm and 2,000-250-μm macroaggregates may have important significance in the enhancement of soil carbon sequestration, fertility, and relief of elevated atmospheric CO2 concentration.