For SOM at the surface layer (0–20 cm), >40-yr age-group had a
36% increase in concentration, 37% increase in storage, and 21%
increase in distribution within the soil profile, while in 60–80 cm
soil there were decreases of 35% for SOM concentration, 37% for
SOM storage, and 36% for SOM distribution within the soil profile
(Fig. 1). These contrary temporal changes resulted in no changes
in SOM storage and distribution on overall 80 cm soil profile
(P > 0.05), and a much moderated increase (9–15%) in SOM concentration
in >20 age groups with respected to