An important factor that can influence contamination of water with nitrate or phytosanitary products is primarily land-use change including the shift in land use from grassland to arable crop use. This shift is important, because, when a grassland is tilled, due to the mineralisation of organic matter from aboveground and underground parts of the grassland, it transfers a significant amount of nitrate to the environment.
In areas where arable crops dominate, soils often contain more readily plant available nitrogen (Nmin), especially after harvest and when soils are left bare. Conversely, when a crop plot is converted to a grassland plot, a decrease in soil nitrate levels is usually measured.
Indicators for land use change can be derived from land use indicators by the introduction of a time sequence.