Weed harrowing in winter cereal under semi-arid conditions

Five field experiments on barley and wheat have been carried out in North-Eastern Spain on the same field during the cropping seasons 1999-00 to 2003-04 to compare the effect of different harrowing adjustments on weed control, weed biomass and cereal yield. The variables considered were harrowing timing (pre- or early post-emergence), one or two passes, travelling direction, harrowing depth and speed compared with an untreated control and herbicide. Excepting year 2001, with very little weed emergence, mechanical control as a whole caused a significant weed plant reduction compared to the untreated plots in all years. No influence of harrowing depth and travelling speed and of pre-emergence harrowing were found in the trials. A single harrowing treatment conducted across the sowing direction gave the same or less control compared to harrowing along the sowing direction. Two harrowing passes achieved a higher efficacy than one single pass and little differences were detected if the second pass was conducted the same day, across the sowing direction or 15 days later. Despite herbicide had generally a higher efficacy than the harrowing treatments, in three out of five years it was found a mechanical control with the same control than herbicide. The effect of the different treatments on weed biomass was lower than on weed number and no significant differences were found for grain yield. Considering that an herbicide treatment in the present conditions is three times more expensive than harrowing, a single post-emergence harrowing can be considered a valid option for low and medium-infested cereal fields.