Comparative Analysis of the Physical Characteristics of Water Stable Aggregates in Some Forest and Cultivated Soils of Enugu State, South Eastern Nigeria
Comparative Analysis of the Physical Characteristics of Water Stable Aggregates in Some Forest and Cultivated Soils of Enugu State, South Eastern Nigeria.
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), IyiUkwu (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.
Aggregate stability expresses the resistance of aggregates to breakdown when subjected to potentially disruptive processes (Hillel, 1998). The structural stability of soil aggregates upon wetting has been the subject of a lot of research around the world (Boucher, 2006). Eynard (2004) indicated that measurement of stability of soil aggregates in water is generally used to estimate structural changes due to cultivation, as water is the main agent of aggregate breakdown in cultivated soils of the humid tropics.
The quality of any soil depends on its degree of aggregation. Soils that are well aggregated, which remain stable when wetted, are important for erosion resistance, water retention and availability and root growth. Mbagwu (2003) reported that factors that influence aggregate stability are important in evaluating the ease with which soils erode, the potentials of soils to crust or seal, soil permeability and quasi-steady state infiltration rates, seedling emergence and in predicting the capacity of soils to sustain long term crop production.
Some researchers observed that soils with low Mean Weight Diameter (MWD) have the potential to erode faster than those with high MWD because detachability is lower with the later (Igwe and Ejiofor 2005). The stability of soil aggregate is affected by soil properties that change relatively little, that is, the inherent composition (texture, type of clay, calcium, sodium, aluminum and iron content) and properties that change in response to vegetation and management (Carter, 2002).
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