Sugar beet field trials were conducted at two sites in Southern Lower Saxony to compare mechanical (hoeing), chemical (herbicide spraying) and combined mechanical-chemical weed control operations in their weed control efficacy, and in their effect on mulch coverage and soil erosion by water. Three treatments were tested in four replications at both sites. To measure runoff and soil erosion, rainfall simulations were carried out for mechanical and chemical treatments after completion of the last

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... weed control operation. The cumulative soil loss was twice higher in mechanical than in chemical treatment in Sieboldshausen (p-value=0.03) but was eight times lower in mechanical than in chemical treatment in Obernjesa (p-value=0.004). The cumulative runoff was not significantly different between treatments in Sieboldshausen but was again significantly lower for hoeing than for spraying in Obernjesa. Also the effect on weed control efficacy by second weed control operation (2-4-leaf-stage) was site-specific, with no effect in Sieboldshausen and significantly reduced efficacy of mechanical weed control in Obernjesa. Mulch coverage loss due to the second weed control operation was significantly higher for mechanical than for chemical treatment at both sites.