Soil Organic Matter Distribution of Contrasting Landscapes in Egbema, Southeastern Nigeria

Abstract

Soil organic matter plays significant role in soil physical, chemical and biological properties and also in the global carbon circle. Distribution of SOM in three different landscapes (Levee, Floodplain and Upland) in Egbema, Southeastern Nigeria was evaluated. This included the evaluation of total organic carbon (TOC), labile organic carbon (LOC), non-labile organic carbon (NLOC), cold water carbohydrate (CWC), hot water carbohydrate (HWC), dilute acid carbohydrate (DAC), mobile or free, bound to cations and strongly bound humic acid humus compounds (MH, Hcad and Hsad respectively), mobile or free, bound to cations and strongly bound fulvic acid humus compounds (MF, Fcal and Fsad respectively), total humic, fulvic and humic : fulvic acid ratios (TH, TF and TH: TF respectively) and the degree of organic matter humification (DH). Relationship between selected soil properties and the SOM components was also determined. The TOC, LOC and NLOC differed significantly (LSD 0.05) with depth and ranged from 5.80-25.50, 1.4-3.90 and3.80-21.60 g kg^-1 respectively, with means varying as 2.70, 1.80 and 2.13 (LOC), 18.43, 14.33 and 6.63 (NLOC) and 22.03, 16.13 and 8.77 g kg^-1 for levee, floodplain and upland landscapes respectively being higher in the levee compared to the others. The CWC and HWC significantly (LSD 0.05) decreased but DAC irregular with depths, with means varying as 0.37, 0.47 and 0.17 mg kg^-1 (CWC), 0.60, 0.73 and 0.50 mg kg^-1 (HWC) and 8.20, 8.20 and 6.13 mg kg^-1 (DAC) in the levee, floodplain and upland landscapes respectively and higher in the floodplain than the others. Humic and fulvic acid fractions distinctly varied with soil depths and landscapes with concentrations being an increasing order of free or mobile < bound to cations < strongly bound or high molecular weight humus compound fractions. Total humic and fulvic acid contents varied with soil depths, with mean humic acid contents higher in the levee and fulvic acid in the floodplain compared to the other landscapes. Variation in humic: fulvic acid ratio showed that the SOM was more matured and stable with respect to the levee followed by floodplain and upland landscapes. Degree of humification varied with soil depth with means decreasing as Upland > floodplain > levee. Concentrations of the SOM components were affected by soil properties. Results of this study showed that SOM storage varied as levee > floodplain > upland suggesting that the capacity of the levee for carbon sequestration was better than the other landscapes.

Keywords: SOM, landscapes, Egbema, Southeastern Nigeria and carbon sequestration