Behavior of nitrate in a heterogeneous field soil : measurements and modeling on different spatial scales

An experimental study was conducted to characterize the behaviour of nitrate in an agricultural field during winter. The experiment embraced measurements of the nitrate concentration profiles at 40 plots at the beginning and end of the experiment. Additionally, the nitrogen inputs through rainfall and fertilization were assessed throughout the experiment. To estimate the transport properties of the soil at the 40 plots, a bromide tracer experiment was carried out. The transport of this conservative tracer in the plots could be described as a convective dispersive process. To predict the nitrate concentration profile at the end of the experiment from the initial concentrations, convective dispersive transport was assumed along with zero‐order kinetics to describe nitrification. On plot scale, this simple model performed poorly. This was attributed mainly to the spatial heterogeneity of the fertilizer dosage. However, when the local model was scaled up to describe the field‐averaged behaviour of nitrate, the deviation of the model from the measurements was significantly smaller. From this, it can be concluded that in certain situations, simple models can provide adequate descriptions of processes which, though highly complex on the local scale, become accessible when averaged over larger areas.