2.4. Experimental
Using an ÔArc-View version 3.1Õ Geographic Information
System (GIS), the field was divided into 25-m
grid squares to give a total of 124 ÔpotentialÕ sampling
points at each grid node (Fig. 2(a)). Twenty of these
points, which fell on or close to the existing ®eld
boundaries, were subsequently omitted to minimise
edge eects, leaving a total of 104 ÔactualÕ sampling
points.