Late Fall Site‐Specific Soil Nitrate Upper Limits for Groundwater Protection Purposes

For temperate regions, such as Germany, a simple management model is developed, with which NO 3 seepage losses during winter can be estimated, when the amount and distribution of soil NO 3 in late fall are known. The semi‐analytical, one‐dimensional model is developed for homogeneous soils. The model is derived for steady‐state flow conditions at a constant soil water content (field capacity). Essential part of the model is a solute transport equation based on mixing‐cell theory. Sample calculations show that when the height Δz of the mixing‐cells is chosen such that Δz = 2 D/v , where D is the soil dispersion coefficient and v is the pore water flow velocity, mixing‐cell model results compare well with results from convective‐dispersive models. The advantage of mixing‐cell models compared with convective‐dispersive models is that mixing‐cell model solutions frequently appear as simple mathematical expressions. With the model sample calculations concerning NO 3 seepage losses during winter were carried out for a variety of site conditions. The calculations show that NO 3 seepage losses vary considerably, even when the initial amount and the distribution of the soil NO 3 ‐N are the same. The calculations also show that if a limit is set for the total amount of tolerable NO 3 seepage losses during winter, site‐specific late fall upper limits for soil NO 3 ‐N can be derived. A table of such values, for a wide range of site‐conditions, is presented.