Überschusswasser

Überschusswasser is a term used in hydrology and soil science to denote the portion of water in the soil that is not retained by soil particles and plant roots and is free to drain under gravity. It is commonly referred to as gravitational water and is distinguished from the water held at or below field capacity, which represents plant-available and capillary water.

Origin and fate: After rainfall or irrigation, the soil may become saturated and gravitational water drains downward until the soil moisture reaches field capacity. The amount of water that drains away during this process is the Überschusswasser. Its magnitude depends on soil texture and structure, initial moisture, rainfall characteristics, and drainage conditions. In permeable soils or on slopes, Überschusswasser may appear as deep percolation or surface runoff, contributing to groundwater recharge or streamflow.

Hydrological context: In the water balance, Überschusswasser is a temporary component that does not stay in the root zone; it influences leaching of nutrients and the design of drainage systems. In agriculture and horticulture, understanding Überschusswasser helps prevent waterlogging and supports irrigation scheduling to optimize soil moisture.

Measurement and management: Überschusswasser is inferred from soil moisture profiles and field capacity values, and it can be estimated with infiltration tests and hydrological models. Practical management measures include appropriate drainage, controlled irrigation, and soil amendments to improve infiltration and drainage, thereby influencing how much water becomes Überschusswasser in a given period.