Nitrate leaching is a naturally occurring process, it occurs when nitrate leaves the soil in drainage water. Nitrate is soluble and mobile. It is no problem when it is within the root-zone, but once it gets into the ground water and other fresh water bodies it is an environmental pollutant.
Nitrate levels in fresh water have become an important indicator of pollution and they are the focus of national and regional government strategies to improve water quality. Farmers must understand the risk of leaching and manage their crops to minimise losses from their land.
The amount of nitrate leached is governed by two factors:
Nitrate levels in the soil + Drainage from saturated soils
Most crops prefer to take up nitrogen as nitrate. Having an available supply of nitrate when the plant needs it is an asset for the crop. Having too much nitrate in the soil can be a liability.
Farmers can reduce leaching risk by matching their fertiliser applications to the crop demand. Split applications are a less risky option. In regions that get dumps of rainfall during spring and summer, a slow-release fertiliser may be the most economical solution