Autumn ridging is a modified version of the ridge tillage system. Instead of setting up ridges during the growing season, they are

established in autumn and left for the winter. Previous studies have documented positive effects of autumn ridging on potato yield

and we hypothesized that subsoiling could enhance these effects. To determine the effect of autumn ridging and inter-row subsoiling

on potato yield and quality a field experiment was conducted on sandy soil from 2001 to 2003. Autumn ridging resulted in an

average total and marketable tuber yield of 25.6 and 9.2 t ha1, which was not significantly different from the average total and

marketable yield of 25.6 and 8.9 t ha1 with ploughing. However, autumn ridging significantly reduced the incidence of black scurf

from 2.5% to 2.2%. Inter-row subsoiling in the growing season significantly increased marketable potato tuber yield from 8.4 to

9.6 t ha1 and reduced the occurrence of malformed potatoes from 9.3% to 7.5%, irrespective of tillage treatment and irrigation

level. There was no significant interaction between autumn ridging and subsoiling. The beneficial effect of subsoiling on marketable

yield was driven by a 48.5% increase in the dry year of 2001. Subsoiling reduced the incidence of common scab from 7.8% to 6.9%

when irrigation was reduced. It is concluded that at least three factors may modify the effects of subsoiling: Soil water status in the

growing season, precipitation immediately before and after the subsoiling operation, and crop growth stage at the time of subsoiling.

# 2006 Elsevier B.V. All rights reserved.