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Abstract In a mixture of crop and weeds, competition exists between plants for incident solar radiation, soil nutrients, and soil moisture. Integrated weed management manipulates cropping‐system factors such that the competitive relationship favors growth of the crop at the expense of the weeds; however, relatively few studies have been reported on the influence of cropping‐system factors on crop‐weed competition. The objectives of this study were to evaluate the impact of weed interference on the performance of four maize ( Zea mays L.) hybrids and to examine the influence of soil N level on the competitiveness of the hybrids. Experiments were conducted during 1990, 1991, and 1992 at the Elora Research Station, Elora, ON, on a London loam (Aquic Hapludalf) soil that had been tile drained. Maize hybrids included an old hybrid (Pride 5, released in 1959) and three more recently released hybrids (Pioneer 3902, DEA, and Pioneer 3953). The maize hybrids were grown at 7 plants m −2 under three weed pressures and at two soil N levels. Weed pressures were established by varying the weed‐free period after planting: all season (weed free), planting to 5‐ to 7‐leaf stage of maize (medium weed pressure), and planting to 3‐ to 4‐leaf stage of maize (high weed pressure). Maize dry matter accumulation and grain yield were measured. Mean grain yield of four hybrids across 3 yr was 65% higher in the high‐N, weed‐free treatment than in the low‐N, high‐weed‐pressure treatment. The effect of weed interference on maize grain yield was higher at low than at high N. Maize hybrids responded differently to N level and weed interference; yield of the old hybrid was reduced more by low N and weed interference than yields of the new hybrids. Consequently, selection of maize hybrid and soil N level should be an integral part in the design of a weed management system.
Tollenaar et al. (Fri,) studied this question.