Improving weed management in organic spring barley: physical weed control vs. interspecific competition

P>Few options exist for effectively managing weeds in organic spring cereals. Establishing a competitive crop through increased seeding rate provides improved weed suppression, but competition with inter-row weeds is delayed, compared with an alternative, more uniform spatial pattern of sowing. We speculated that (i) enhanced interspecific competition or (ii) improved physical weed control with a strategy of wide-row sowing and inter-row hoeing would both provide better weed control than current regional organic practices. However, whether one of these strategies is superior to the other depends on an economic analysis of the relative costs of seed and equipment. We tested this hypothesis in two field experiments with spring barley (Hordeum vulgare) at three row spacings (11.4, 17.7 and 22.8 cm), and by sowing in a more uniform pattern, using condiment mustard (Sinapis alba) as a surrogate weed. Standard regional organic practice (17.7 cm rows, 200 plants m-2) had the highest weed biomass at the conclusion of both seasons. Weeds in this treatment accounted for 57% of total above-ground plant biomass in 2007 and 27% in 2008. The more uniform sowing pattern reduced weed biomass by 26% compared with the regional standard, averaged over 2 years of the experiment. Although we expected enhancing crop competition to be the most economical practice, high cost of organic seed resulted in intermediate net returns. At high weed density, the wide row strategy offered improved weed control, yields and profitability. However, with lower weed density, spring barley was sufficiently competitive that it did not benefit from cultivation.