Bulk density and organic carbon contents of soil pedons influenced by different tree species

Abstract. Bulk density and organic matter content of soil are important soil attributes used in predicting the productivity potentials of soil and overall soil quality. The distribution of soils bulk density and organic carbon in horizons of soil pedons under different three tree species (Hevea brasiliensis – rubber, Pentaclethra macrophylla – oil bean and Irvingia gabonensis – ogbono) in Owerri, Southeastern Nigeria were investigated. A random survey method was used in field sampling. In all, three profile pits were dug, one in each site. A total of 36 soil samples were collected and analyzed for the study. Samples were collected at different horizon levels (A, AB, Bt1 and Bt2). Three representative samples were collected from each horizon. Bulk density, organic carbon and other routine analyses were performed using routine laboratory techniques. Mean, coefficient of variation and correlation analyses were analyzed. From the results obtained bulk density increased with depth, ranging from 1.05-1.81 g cm-3 in the rubber plantation, 1.02-1.70 g cm-3 in ogbono plantation and 1.11-1.57 g cm-3 in oil bean plantation. Bulk density decreased with the increase the organic carbon content. However, mean bulk density values irrespective of tree species did not exceed critical limits ranging from 1.28 to 1.32 g cm-3 as appropriate. Organic carbon ranged from 0.06-0.89 g kg-1 in rubber plantation, 0.42-0.87 g kg-1 in ogbono plantation and 0.72-1.25 g kg-1 in oil bean plantation. The epipedal horizons contained higher organic carbon than the endo-pedal horizons. The average organic carbon contents of the pedons were lower than the critical value irrespective of the tree species. The oil bean plantation had higher organic carbon and total nitrogen than the ogbono and rubber plantation while the ogbono plantation contained higher available phosphorus than the other two plantations studied