Soil ridge geometry for green control in French fry potato production on loamy clay soils in The Netherlands

Green potato (Solanum tuberosum L.) tubers are rejected by the processing industry. Therefore their amount should be reduced to minimum. The objective of this study was to assess the reduction of greening of new French fry varieties in experiments conducted from 1998 to 2001 on ridge qualities like geometry and the compression and crumbling degree of the loose soil in the ridge. The experiments were mainly carried out on the experimental husbandry farm Westmaas on a Calcaric Fluvisol having a clay content of ca. 200 g kg¿1. French fry potato varieties used were Agria and Fambo, whereas Bintje was used as a reference. Row spacings were 0.75 m (30 in.) and 0.90 m (36 in.). Net ridge size was determined by the internal height (distance between the plate and the top of the ridge) and by the width of the top of the ridge combined with planting near the surface of the plate. For the traditional French fry variety Bintje a reduction in greening was achieved by ridges having a gross size of 0.06¿0.07 m2. New French fry potato varieties like Agria and Fambo, however, are characterized by higher yields, larger cluster widths and longer tubers than Bintje. These properties favor the greening of tubers and require adjustment of the ridge geometry. Increase of the internal height and of the top width were found to be crucial to reduce greening of tubers to minimum. An increase of the top width of standard 0.75 m ridges from 0.15¿0.18 to 0.25 m combined with an internal height of 0.18¿0.20 m was realized by the so-called plateau ridges. This ridge type required ca. 0.04 m deeper seedbed than the depth of the seedbed for standard 0.75 m ridges. Without deeper loosening of the seedbed such larger ridges could also be realized by an increase of row spacing to 0.90 m. Net yields of new French fry varieties of plateau and 0.90 m ridges were generally similar or higher than the yields of standard 0.75 m ridges with the same internal height. With 0.90 m ridges over-sizing occurred sometimes. Greening of new varieties of French fry potatoes was reduced to minimum by the new knowledge on ridge geometry: an increase of the internal ridge height to 0.18¿0.20 m, a top width to 0.25 m and reduction of cracking by relatively coarse, non-compressed ridges.