Variation within fields of potentially available nitrogen using the hot KCL technique

In February 1996, ten fields in the Lothians were chosen which had been ploughed but not yet sown with spring barley. They were sampled on a 30 metre grid and potentially available nitrogen (PAN) was measured by extraction with hot potassium chloride solution. Differences between fields accounted for 72% of the sums of squares for differences in PAN and only 28% of the sums of squares was contributed by differences within fields. The field means ranged from 52 to 101 kg N/ha and the standard deviation of samples within the same field from 4.9 to 17.1 kg/ha. Some fields had well defined spatial trends but for other fields, the measured values appeared to be randomly distributed. Contour maps were drawn for all fields but may be of limited value for the fields without pronounced trends.