The effect of sowing strategy, row distance and mechanical weed control on weeds and yield in organic winter wheat

A series of field experiments were carried out in winter wheat grown under organic conditions in Denmark on fields with different weed pressure. The treatments were sowing strategy (normal sowing time, late sowing and false seedbed), row distance (12 cm and 24 cm row distance) and weed control method (untreated, mechanical weed control (weed harrowing at 12 cm supplemented with row hoeing at 24 cm), and herbicide weed control). Weed biomass was largest at the normal sowing time and was reduced by mechanical or chemical weed control. Row distance alone did not generally influence weed biomass, but mechanical weed control reduced weed biomass at a row distance of 24 cm. Normal sowing time gave rise to about 10% higher yield. The effect of weed control on yield was dependent on the weed pressure. At low weed pressure, mechanical weed control caused a yield decrease of 11% compared to untreated or herbicide. At intermediate weed pressure there were no differences, whereas at high weed pressure, mechanical weed control caused a 15% and no weed control a 25% yield decrease compared to herbicide treatment. False seedbed can contribute to a decrease in the soil seed reserve.