Seed distance in relation to row distance: Effect on grain yield and weed biomass in organically grown winter wheat, spring wheat and spring oats

Inter-row hoeing at wide row distance can form part of a weed management strategy in which mechanical and cultural tools are combined. Crop plant distribution is a key parameter for maintaining high grain yield levels and weed suppressive ability in such a system. The influence of seed distance in relation to row distance was studied in 10 field trials on spring wheat, spring oats and winter wheat. Post-emergence weed harrowing was applied at 12–12.5 cm row distance and inter-row hoeing at 24–25, 36–37.5 and 48–50 cm distance. Three seed distances within rows were applied: (1) Normal for the region, (2) reduced to 2/3 the normal, and (3) reduced to half the normal. To obtain normal seed distance at 12–12.5 cm row distance, 400, 525 and 600 germinable seeds m−2 were sown in winter wheat, spring oats and spring wheat, respectively. The highest grain yields were found after weed harrowing at row distance 12–12.5 cm; 5550 kg ha−1 of winter wheat, 3765 kg ha−1 of spring oats and 3105 kg ha−1 of spring wheat. Inter-row hoeing at the row distance 24–25 cm, while keeping seed distance constant, lowered grain yields of all crops by 12–16%, but had no significant influence on weed biomass. Increasing the row distance from 24–25 to 36–37.5 cm reduced grain yield by 450–460 kg ha−1 in winter wheat and oats, while a further increase to 48–50 cm reduced yield by an additional 450–520 kg ha−1 in all crops when averaged over seed distances. At row distance 24 cm and wider, grain yield of winter wheat and oats increased more when the seed distance was reduced from normal to 2/3 of normal than when reduced from 2/3 to half the normal distance. In inter-row hoed winter wheat and spring oats, weed biomass increased with increasing row and seed distance. Within the range of seed distances used in this study, a reduction to half of normal was considered as the most profitable when these crops are sown at row distances 24 cm or wider. There was no indication that seed distance in spring wheat should be changed when using wide row distances. Increased row and seed distances improved the content of gluten and reduced the content of starch in wheat grain, while protein content was increased in the grain of all crops. The response to treatments in terms of grain content of ergosterol was inconsistent between winter and spring wheat.

► The influence of row distance and intra-row seed distance on cereal grain yield and weeds was examined.
► Increasing seed and row distances reduced grain yield in winter wheat and oats, but not in spring wheat.
► Protein content was increased in the grain of all crops.
► In wheat grain, gluten content was improved while starch content was reduced.
► The influence of seed distance on response variables was similar, irrespective of row distance.