Abstract

The Information on the effect of different land use systems on the aggregate stability and carbon sequestration is crucial for the recommendation of efficient land management practices. This study was conducted to evaluate the variation in aggregate stability and carbon sequestration under different land use systems in two agro ecological zones of south eastern Nigeria. The agro ecological zones were derived savannah and rainforest while the land use systems studied were cultivated, excavated, fallow, forest and grazing. The soil samples were collected at a depth of 0- 15cm using transect method and analyzed for particle size distribution, water stable aggregates, mean weight diameter, % aggregate stability, total organic carbon and organic carbon associated with water stable aggregates (4-2mm, 2-0.25 mm, 025-0.053 mm).The data collected were subjected to analysis of variance (ANOVA) in randomized complete block design (RCBD). The results show that land use did not affect particle size distribution and the effect of agro zone on aggregate stability indices (WDC, DR and MWD) was not significant(P<0.05). However, ASC (aggregated silt + clay) and 3%AS (aggregate stability) in the derived savannah were 29.5% and 11.7% higher than the rainforest respectively. The MWD was reported to be greater in fallow, forest and grazing than cultivated and excavated. The percentage water stable aggregates were not significantly affected (P<0.05) by land use but grazing gave significantly higher values than excavated, cultivated, fallow and forest for 4-2 mm and 2-0.25 mm. The overall result has shown that forest and grazing land use systems are superior in terms of improving soil quality. Therefore, fallow land can be converted to grazing while the addition of organic material is recommended in arable and excavated land use.

Key words: ASC (Aggregated silt + clay), MWD (mean weight diameter), DR (dispersion ratio), %AS (percentage aggregate stability), WDC (water dispersible clay).