This chapter discusses the methodological basis for estimation of the potential for nitrate uptake, as well as the implications for nitrogen (N) uptake by deep roots. It shows that the importance of root depths for N uptake in modeling by simulating soil nitrate left by crops at harvest by use of the EU-rotate_N model. Experimental work on root distribution and leaching losses below annual crops is often based on this assumption, and it is common practice to limit root and N-leaching studies to the soil surface layers. There are methodological difficulties in working at depths greater than 1 m. Therefore, data on roots below 0.6–1-m depth is often missing, and root studies often show some roots at their deepest measuring depth. The potential for N uptake below 1-m depth was found to be high for all crops studied except for winter rye. The potential N-uptake rate varied greatly between species.