Hydraulic Conductivity [1]

A measure of the rate of water flow, typically saturated water flow, through the soil. In very general terms this might be thought of as indicative of a soils potential drainage rate.

Hydraulic conductivity (HC) is influenced by a number of different factors, including:
• The water content of the soil. A drier soil will have a lower HC, with the soil typically needing to reach field capacity before any significant outflow of water is achieved. HC is at its maximum when a soil is saturated.
• Water and soil temperature affect the rate of flow. A warmer water is more fluid (i.e. having a lower viscosity) than a colder one.
• A soil with good, continuous, connections between the soil pores will have a higher HC than one without good connections. A well-structured and aerated soil with a continuous vertical porous route for water to move through will have an increased rate of HC than a soil with broken connections, which are effectively cul-de-sacs for water movement.
• The extent and size of pore spaces have a significant influence on water movement. Macropores will allow for greater transmission of water than micropores. Compacted soils will have relatively few macropores and lower rates of HC than well-aerated and well-structured soils.

HC can be used as a performance standard for a turfgrass area to distinguish it from infiltration rate. The ability of a soil to continuously remove water at a stated rate is arguably more important than the often-short term and initial action of being ‘topped-up’ with infiltration water, which may then stay for prolonged periods in a soil due to poor soil drainage potential. Infiltration might be good, but if this is for a short term only and then the water effectively backs up due to poor HC rates then waterlogging will occur and this is will result in poor playing conditions and match cancellations, especially for sports played over the winter period.