A key prerequisite, however, is that the pattern of high and low DM and N-yielding areas should remain constant from year to year, or alternatively, that there is the technical capability to monitor N variability, in real time, over the period during which fertiliser is to be applied. It is worth noting, therefore, that a broadly similar distribution of DM yields was observed in the
field by farm staff during at least three previous consecutive growing seasons, which would seem to confirm
its consistency or stability with time.