Inter-row hoeing for weed control in organic spring cereals-Influence of inter-row spacing and nitrogen rate

Inter-row hoeing has become increasingly important for weed control in organic spring cereals since the introduction of automatic steering systems. The technology requires a widening of current inter-row spacing for spring cereals in order to provide sufficient room for accurate operation of a hoe share between crop rows. However, there is considerable uncertainty about the optimal combination of inter-row hoeing, inter-row spacing and nitrogen (N) rate in terms of weeding effectiveness and crop yield. The aim of this study was to investigate the effect on weed and crop growth of the interaction between five inter-row spacings (125, 150, 200, 250, and 300 mm) and two N rates (50 and 100 kg NH4-N ha−1). Three field experiments were conducted in spring barley and two in spring wheat. One hoeing pass was applied for each inter-row spacing using a share width that worked 15-47 mm from the crop row. The immediate effect on weed numbers following hoeing was a 80-90% reduction in barley and a 63-80% reduction in wheat, but with no significant differences between spacings and N rates. However, the effect on weed biomass at crop anthesis was minor in barley because the crop itself substantially suppressed weed growth. Spring wheat was less competitive and inter-row hoeing reduced weed biomass by 60-70% compared to the standard 125 mm spacing without hoeing. The widening of inter-row spacing appeared not to reduce crop yield or grain quality. Prerequisites for successful inter-row hoeing in spring cereals include retained crop stands when increasing inter-row spacing and the avoidance of crop injuries from inaccurate steering.