Soil compaction characterization and influence on plant nutrient uptake under different soil conditions

Changes in soil bulk density occur as a result of soil compaction or other soil management practices. This dissertation was based on two broad objectives; (a) to study the effect of bulk density on the growth and uptake of phosphorus and potassium by corn under different soil water regimes and fertilization; (b) to measure, characterize and predict the effect of changes in bulk density on some soil hydraulic properties. In growth chamber experiments on a Boelus loamy sand (Mixed, mesic udorthentic Haplustoll), root length, root area and uptake of P and K were decreased by increasing bulk density whereas root radius was increased. Uptake of P and K per unit root area and shoot P composition increased at higher bulk densities. Irrigation frequency influenced root and shoot dry weights and P uptake at moderately high soil P concentration but had no effect on shoot dry weight under high soil P concentration. Root radius was influenced by irrigation frequency when the soil was adequately fertilized. Soil bulk density interacted with irrigation frequency on influencing root radius when the soil was adequately fertilized. Soil water diffusivity, soil water characteristics and pore size distributions were determined for the soil compacted to different bulk densities. A modified procedure for the calculation of the soil water diffusivity from a one-step outflow experiment was presented. Moments, skewness and kurtosis of the pore size distributions were calculated. Regression analysis between the parameters of the pore size distribution and the soil bulk density showed significant correlations at 95 percent probability level or better. An evaluation of the Arya and Paris model that predicts the soil water characteristics curve from the soil bulk density, soil particle density and soil particle distribution was carried out. A modified procedure that takes into account soil particle aggregation was also presented