Infiltration Rate (IR)
Definition - What does Infiltration Rate (IR) mean?
Infiltration rate (IR) is the speed at which water flows through soil. When water sits on the soil surface, atmospheric pressure, suction and gravity combine to make the water flow through to the root systems and further. Winemakers monitor the IRs of their vineyards to ensure that the root system of their vines is getting enough water and nutrients. High IRs reduce run-off and risks of water logging; very high IRs may mean that some nutrients do not make it to the roots, instead seeping down deeper into the soil; and low IRs mean water won’t reach the roots.
WineFrog explains Infiltration Rate (IR)
Infiltration rates are expressed in unit length (usually “mm”) per unit time (usually “hour”), implying that the rates are tracked vertically, but do not take into account horizontal diversion. When water seeps into the soil, it doesn’t do so at just one point, but spreads over the surface and drips down. The IR only monitors/tracks the vertical depth the water travels. The ideal farming IR is 50mm per hour. This IR means that even during a heavy rainfall, water will not puddle or run-off.
IR is effected by soil type. Different soil types have different base IRs:
- Clay - 10 to 20mm per hour; good to average soil structure
- Calcium-rich soils (like marlstone) - 4 to 8mm per hour
- Clay-loam and Clayey-Marls: 20 - 50mm per hour; found on many lower-slope vineyards and retains good soil structure
- Loam to sandy soils - 50mm per hour; good soil structure
- Sandy and calcareous (limestone) - 150 to over 200mm per hour; drains excessively well and does not retain water well
- Bare soil - 3 to 5mm per hour; IR is the lowest when there is no vegetation on the surface.
Soil management also plays a role in the quality of the IR. Degraded soil structure, deep tillage, herbicide, pesticide use, frequent traversing (being walked upon), shallow water tables, surface crusting and more can have a negative impact on the IR. These events can cause soil erosion (where the soil shifts and washes away with the water) or hardpan (the compacting of the soil directly under the top layer that creates an extremely dense layer of soil that prevents the water from making it through to the next layer).
The maximum rate at which a water enters the soil is called the “infiltration capacity”.