COMPARATIVE ANALYSIS OF THE PHYSICAL CHARACTERISTICS OF WATER STABLE AGGREGATES IN SOME FOREST AND CULTIVATED
ABSTRACT
A study was conducted to evaluate the physical changes that occur in the soil due to
conversion of forest to arable land. Six locations in Enugu State that were selected for
this purpose include Ugbo-Okpara (Li), Ugbo-nabo (L2), Ugwogo-Nike (L3), Iyi-
Ukwu (L4), Edem (L5) and Ugwo (L6). Soil parameters determined include bulk
density, saturated hydraulic conductivity, macro porosity, micro porosity, total porosity, organic carbon, pH, Dithionate citrate bi-carbonate (DCB) Iron oxide, particle size distribution, and micro aggregate stability indices. With respect to the water stable aggregate, the indices used for evaluation include particle size distribution, aggregate size distribution of WSA, mean weight diameter, aggregate stability water retention by WSA at both -33kpa and -1500kpa, available water capacity, organic carbon, aggregated silt plus clay (ASC), water dispersible clay (WDC) and clay dispersion index (CDI).
Soils of both land use types were coarse to moderately fine texture, with
an average pH of 3.95 and 4.1 in the cultivated and forest land use respectively. In the
soil, cultivation significantly (P ≤ 0.05) increased bulk density by 17 %, reduced
hydraulic conductivity, macro porosity, micro porosity and total porosity by 38 %, 23
%, 19 % and 21% respectively. Soil organic carbon and Dithionate citrate bicarbonate
iron oxide was reduced by 34 % and 6.7 % respectively. Land use had significant effect
on aggregated silt plus clay but no significant effect on water dispersible clay, clay
flocculation index and clay dispersion index. However significant effect due to the
interaction of land use and location was observed in these micro-aggregate stability
indices which imply that variation due to land use was dependent on location. With
respect to the water stable aggregates, cultivation reduced the macro aggregates and
increased the proportion of the smaller (< 0.25mm) sized aggregates. The mean weight diameter and aggregate stability declined by 21 % and 50 % respectively. Water retention at -33kpa and -1500kpa were not affected by land use while a slight but significant (P ≤ 0.05) influence on available water capacity was observed. Particle size distribution of the WSA was changed with cultivation of forest soils. aggregated silt plus clay and water dispersible clay and SOC declined by 20 %, 15 % and 25 %
respectively while the clay dispersion Index increased by 2%. The interaction effects of location, aggregate size and land use demonstrated that cultivation improved the
physical properties of the WSA in L1, L2 and L3 while L4, L5 and L6 were adversely.
