Humeomics to evaluate the molecular dynamics of organic matter in soils under different management practices

We applied the recently introduced Humeomic methodology for the fractionation of humic substances, to separate fractions of organic matter molecules directly from soil. The in situ fractionation included: extraction by an organic solvent, transesterification by boron trifluoride in methanol, methanolic alkaline hydrolysis, and cleavage of ether and glycosidic bonds with HI. A sandy loam soil near Torino classified as Typic ustifluvent and with an organic matter (OM) content of 1.7% was subjected to the direct Humeomics. In order to study the effect of soil management, the fractionation was applied to an undisturbed control (CONT) soil, and to a soil undergone traditional (TRA) tillage (moldboard plowing, 30cm deep) and mineral fertilization after one year (2006) and three years (2008). The unbound fraction (ORG1) corresponded only to 1% of OM, while the weakly bound ester fractions either organo-soluble (ORG2) or hydro-soluble (AQU2) were the most abundant fractions in soil, being more than 50% of OM. The corresponding strongly bound ester fractions (ORG3 and AQU3) accounted for 10% of OM, while the remaining organic material was found as strongly bound ethers and extracted with sodium hydroxide from the final Humeomics residue. Interestingly, the ORG2 fraction in the TRA soil was 300-500% larger than in the CONT soil. This is an evidence of the change in molecular aggregation of OM induced by the applied soil management. Moreover, the soil treated with the Humeomic approach delivered 300% more organic material than that extracted using sodium hydroxide, thus suggesting that the application of the Humeomic fractionation in soil is liable to highlight the nature of SOM in an unprecedented manner.