Estimating Soil Bulk Density and Total Nitrogen from Catchment Attributes in Northern Ethiopia
Even though data on soil bulk density (BD) and total nitrogen (TN) are essential for planning modern farming techniques, their data availability is limited for many applications in the developing word. This study is designed to estimate BD and TN from soil properties, land-use systems, soil types and landforms in the Mai-Negus catchment, northern Ethiopia using stepwise multiple regression (SMR) and generalized linear model (GLM) analyses. Different soil properties and other catchment attributes were collected following a standard procedure. The SMR analysis showed overall model coefficients of determination (R2) of 0.91 and 0.89 with significant F-statistics for the relationships of BD and TN, respectively, with soil properties, land-use and landforms. In addition, the GLM analysis resulted in an overall R2 of 0.92 with significant F-statistic for BD, and an R2 of 0.94 with significant F-statistic for TN. The model coefficients of both analyses for the dependent variables showed higher for organic carbon (OC) as compared to the other variables even though higher values were found from GLM. This study thus confirmed that practices which improve OC can strongly influence the variation of both dependent variables. This study suggested that BD and TN should be estimated based on the relationships explained by the different techniques (analysis) in similar conditions in order to improve data availability; however, the GLM is preferable as it considers the effect of the interaction terms.
Keywords: Bulk density, Total nitrogen, Stepwise multiple regression, Generalized linear model, Mai-Negus catchment.