Effect of Plant Roots and Root Channels on Solute Transport

SINCE many of the practical applications of solute modeling are to situations where crop roots are present, it is necessary to investigate the effect of roots and void root channels on the transport of solutes through soils. In an attempt to do this chloride breakthrough experiments were conducted over a two year period in soil columns packed uniformly with sandy loam or loamy sand. A series of experiments were conducted in bare soil, followed by repeated experiments with wheat plants in the columns, and finally in bare soil again after the wheat crop had died. The loamy sand columns showed significantly higher dispersion than the sandy loam columns in the precrop experiments, but the effective dispersion decreased when the experiments were repeated with plant roots present. The post crop experiment showed the highest dispersion of any of the studies possibly due to the presence of old root channels in the soil. Very little immobile water was present in the precrop experiments, but both the cropped experiments and the post crop experiments exhibited significant pore bypass; immobile water fractions ranged from 11 percent to 39 percent of the total water content.