Relationships Between Aggregate Stability and Selected Soil Properties in Humid Tropical Environment

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The stability of aggregates in the surface soil is crucial to the processes of soil erosion and runoff generation in agricultural lands. Thus, the stability of surface soil aggregates was investigated in an Alfisol, of about 20 hectares of farmland, consisting of a variety of cultivation practices. Selected soil properties (organic matter, available phosphorus, pH, bulk density, moisture content, coarse sand, fine sand, silt, and clay contents) were related to aggregate stability index within the sampled locations. Results showed that while pH, bulk density, organic matter, clay, silt, and coarse and fine sand fractions were normally distributed; aggregate stability, gravimetric moisture content and available phosphorus were log-normally distributed in the sampled population. All aforementioned properties, except available phosphorus and clay content, gave significant linear correlation with soil aggregate stability index with organic matter content giving the highest correlation of 0.76. Stepwise multiple regression showed that only 4 variables (organic matter, bulk density, pH and moisture content) gave significant equational relationship with aggregate stability index, with organic matter being the most significant variable. Factor analysis was carried out to detect if there is any structure among the independent variables. The analyses showed that the variables could be separated into 2 major factor components: (i) organic matter, moisture content, coarse sand, fine sand, silt and bulk density (ii) available phosphorus, pH, and clay content. A multiple regression analysis was then undertaken relating factor component scores to aggregate stability index. The regression equation was significant for the first factor but not for the second. Selecting two variables with highest significant correlations each from the two principal components gave a regression equation expressing aggregate stability index as a function of organic matter and pH of the soil. This equation proved to be significant at 1% level for both variables. Within the studied environment, organic matter and pH are the most important properties to consider when predicting soil aggregate stability.