Deriving the Shannon Index from the soil molecular Humeome serves as a descriptor of soil organic matter stability under different cropping systems

Chemical and Biological Technologies in Agriculture

Table 1 Shannon index (SH), SH multiplied by the % OC in the specific molecular class, and their respective total values (SH_tot) for all the molecular classes, derived from the molecular soil humeome for Control, Maize after 1 year (Maize 1) and 3 years cultivation (Maize 3) of the short-term experiment

Molecular classes^a	CONTROL^b		MAIZE 1^c		MAIZE 3^c
Molecular classes^a	SH	SH × % OC	SH	SH × % OC	SH	SH × % OC
AA/AM/IM	1.135 ± 0.035	0.033 ± 0.001	1.665 ± 0.020	0.169 ± 0.002	1.601 ± 0.024	0.132 ± 0.002
AD	2.225 ± 0.103	0.043 ± 0.002	2.365 ± 0.028	0.515 ± 0.006	2.501 ± 0.039	0.576 ± 0.009
BA/BE/HO/PAH	1.532 ± 0.067	0.160 ± 0.007	1.347 ± 0.150	0.009 ± 0.001	1.927 ± 0.027	0.071 ± 0.001
PA/PE/PH	1.649 ± 0.074	0.134 ± 0.006	2.69 ± 0.315	0.188 ± 0.022	2.954 ± 0.040	0.295 ± 0.004
FA/DA/HA	2.118 ± 0.098	0.562 ± 0.026	1.546 ± 0.020	0.394 ± 0.005	2.560 ± 0.037	0.491 ± 0.007
ES/ET/KE/AC/AH/AL	1.992 ± 0.095	0.672 ± 0.032	2.846 ± 0.054	0.106 ± 0.002	2.828 ± 0.039	0.145 ± 0.002
RA/SE/ST	1.490 ± 0.071	0.021 ± 0.001	1.013 ± 0.023	0.044 ± 0.001	1.315 ± 0.039	0.034 ± 0.001
SA/SET/SU	1.345 ± 0.064	0.127 ± 0.006	1.096 ± 0.021	0.104 ± 0.002	1.242 ± 0.014	0.089 ± 0.001
HN	2.715 ± 0.129	0.147 ± 0.007	3.189 ± 0.035	0.553 ± 0.006	3.116 ± 0.048	0.656 ± 0.010
SH_tot	16.201 ± 0.751	1.899 ± 0.088	17.757 ± 0.401	2.082 ± 0.047	20.044 ± 0.298	2.489 ± 0.037
nCPR	0.511 ± 0.003		0.427 ± 0.001		0.369 ± 0.003
SOMR	0.269 ± 0.013		0.205 ± 0.005		0.148 ± 0.002

The SH and the SH x %OC values were used to calculate the nCPR and SOMR ratios, as described in “Methods” section. Standard deviation was derived by analysis in triplicates
^aAA = amino acids; AM = amines; IM = imines; AD = amides; BA = benzoic acids; BE = benzoic esters; HO = heterocyclic oxygen compounds; PAH = polycyclic aromatic hydrocarbons; PA = phenolic acids; PE = phenolic esters; PH = phenols; FA = fatty acids; DA = dicarboxylic acids; HA = hydroxy acids; ES = aliphatic esters; ET = ethers; KE = ketones; AC = alcohols; AH = aldehydes; AL = alkanes/alkenes/alkynes; RA = resin acids; SE = steroids; ST = sterols; SA = sugar acids; SET = sugar esters; SU = sugars; HN = heterocyclic nitrogen compounds
^bBased on the Humeomics fractionation presented by Drosos et al. (2017) in [13]
^cBased on the Humeomics fractionation presented by Drosos and Piccolo (2018) in [28]