Relationships Between Soil Hydraulic Properties, Soil Characteristics, and Distribution of Macropores.

Around 50% of the Danish arable land is tile-drained. Loss of phosphorus (P) to surface waters from tile-drain outflow can be considerable and variable among fields. In order to reduce P loss from tile-drained areas it is essential to know the cause of the variability among fields. Leaching of P to tile-drains will mainly occur through macropores where P can be transported quickly to drains either dissolved or adsorbed to mobile particles. The objective of the current study was to investigate the relationships between morphological descriptions of macropores and the hydraulic properties of the soil. Four different Danish agricultural soils with different clay content were chosen for qualitative morphological description in four trenches along textural gradients. Soil samples were taken in all major horizons in order to measure texture distribution and pH in the laboratory. Using image analyses, the number of earthworm burrows and the size of the horizontal section of these burrows were measured at three depths. At the same depths, saturated and unsaturated conductivity was measured on large soil cores. Earthworm biomass, number of individuals, and development stage was determined for each site. Relationships between simple soil variables and morphological descriptions of macropores and comparisons with measurement of saturated and unsaturated conductivity have been established. Links will be drawn to colloid mobilization and transport.