The experimental cultivation system was based on a disc rotating about a substantially vertical axis. The assembly was mounted on a depth control wheel and set to cultivate at a shallow depth (typically 20 mm) within the crop row. Crop damage was avoided by cutting out a section from the disc's plan profile and rotating it in synchrony with forward movement such that the cut-out always coincided with the regularly spaced transplants (Fig. 1). Variability in plant spacing along the row was accommodated by making small adjustments to the rotational speed of the disc via a phase-lock loop. This mechanism minimised the relative speed between the cultivation device and the soil, thus reducing soil throw and possible contamination of the crop by stones and soil.