A field crop of 3‐month old cabbages was sampled every 2 h from 0600 h until 2000 h. At each sampling, an upper, middle and lower leaf were taken from four plants, and their petiole nitrate status measured by three methods (a) “Merckoquant”; test strips (b) specific ion electrode on a fresh macerated extract and (c) the same electrode on an extract of oven dry tissue. All three methods led to similar conclusions:a.there were very big differences in concentration with leaf position, the middle leaf having the highest;b.there were large concentration differences between plants, especially for the lower leaves;c.the effect of time of day was not significant.