Humic substances in soils of diverse parent materials in humid tropical environment of south east nigeria.

The knowledge of humic substances of soil is essential for soil fertility management and productivity. The study evaluated the humic substances (HS) and physicochemical properties of soils of different lithologies. Twenty composite soil samples were collected at the depths of 0-15 and 15-30 cm in both upland and inland of sandstone (SS), limestone (LS), mudstone (MS), basement complex (BC) and shale (SH) and analyzed for HS and physicochemical properties. HS were higher in surface than subsurface soils and in SH, SS and MS than other parent materials. Humic acid had mean values of 0.649 and 0.683 g/kg, 0.327 and 0.055 g/kg, 0.736 and 1.167 g/kg, 0.976 and 0.839 g/kg and 0.449 and 0.411 g/kg in surface soils of upland and inland in BC, MS, SS, SH and LS. In subsurface soils, average values of humic acid were 0.322 and 0.426 g/kg, 0.055 and 0.012 g/kg, 0.499 and 0.713 g/kg, 0.656 and 0.908 g/kg and 0.276 and 0.047 g/kg in the upland and inland of BC, MS, SS, SH and LS correspondingly. Fulvic acid had averages of 0.237 and 0.3125 g/kg, 0.533 and 0.751 g/kg, 0.297 and 0.707 mg/kg, 0.6524 and 0.568 g/kg and 0.220 and 0.007 g/kg in the surface soils of upland and inland of BC, MS, SS, SH and LS. In subsurface, fulvic acid had means of 0.244 and 0.363 g/kg, 0.227 and 0.328 g/kg, 0.056 and 0.128 g/kg, 0.040 and 0.402 g/kg and 0.001 and 0.415 g/kg in upland and inland of BC, MS, SS, SH and LS respectively. BC was higher in clay content than other parent materials. ECEC correlated significantly and positively with BS, Ca, Na, pH, silt, K and Mg while fulvic and humic acids correlated positively with TN and OM. pH was strongly acidic in soils of upland and varied from medium acid to slightly acid in inland. OC was high in inland and varied from high in MS, SH and SS to low in BC and LS in upland. Available P, TN, exchangeable bases, ECEC varied from low to high while BS was high in soils of both upland and inland.