Competition between sugarbeet and Sinapis arvensis and Chenopodium album, as affected by timing of nitrogen fertilization

The effects of timing of N fertilization (early, standard or late) on compe tition between two sugarbeet cultivars (Ritmo, semi-prostrate; and Rizor, e rect) and two weeds (Sinapis arvensis and Chenopodium album) were studied o ver 2 years at Viterbo. In both years, time of N fertilization did not infl uence biomass, yield and yield quality of the weed-free crop, but early N f ertilization gave higher crop biomass reduction in the presence of S. arven sis and lower crop biomass reduction in the presence of C. album. Root and sucrose yield responded to competition in the same way as biomass. However, percentage reductions were higher, as both weeds affected harvest index. T he two cultivars showed the same response to competition. At the weed densi ties studied, crop competitive ability was favoured by late N fertilization in the presence of S. arvensis and by early N fertilization in the presenc e of C. album. Crop competition only reduced seed production by C, album bu t lowered seed germination of both weeds.