Potato tuber yield and quality and soil inorganic nitrogen as affected by timing of ridging with and without catch crops

Field experiments were conducted on sand and sandy loam from 2000 to 2002 to determine how timing of ridging affects potato tuber yield and quality depending on soil texture and the use of catch crops. On sand, ridging in winter increased soil N availability in the 0–50 cm soil layer in spring from 5.7 to 6.8 mg N kg−1 soil (19%) compared with ridging in autumn (P < 0.001) and from 6.3 to 6.8 mg N kg−1 soil (8%) compared with ploughing in spring (P < 0.05). Catch crops increased soil N availability in the 0–25 cm soil layer in spring from 7.7 to 10.2 mg N kg−1 soil (32%, P < 0.001).With a total and marketable yield of 27.9 and 14.2 t ha−1, respectively, ridging in winter resulted in higher tuber yields than both ridging in autumn and ridging in autumn + tilting and re-establishment of ridges in winter. Yields were comparable to spring ploughing, but because of the ability to perform direct planting of potatoes in the winter ridges on sand, workload was significantly reduced.Catch crops increased total yield from 26.4 to 28.0 t ha−1 (P < 0.001) and marketable yield from 12.6 to 14.6 t ha−1. There was no effect of timing of ridging when catch crops were not used, but a ryegrass catch crop combined with ploughing in spring or ridging in winter resulted in a higher total yield and marketable yield than a cruciferous catch crop mixture combined with earlier ridging (P < 0.05).Besides differences between years, tuber quality was only weakly affected by treatments. Taste quality was improved and the percentage of tubers with common scab, malformation, growth cracks and greening was reduced in 2001 compared with 2002.On sandy loam, there was no effect of timing of ridging on tuber yield and quality. Ridging in winter resulted in similar levels of soil inorganic nitrogen and similar tuber yields as ploughing in winter, but because ridges had to be rotovated in spring before planting to create a sufficiently loose soil, workload was not reduced. On sandy loam, catch crops significantly reduced soil N availability in all soil layers in spring (P < 0.05).It is concluded that ridging in winter, especially in combination with a ryegrass catch crop, represents a potent alternative for organic potato production on sand but not on sandy loam.