TILLAGE AND ROTATION CROP EFFECTS ON WEED DYNAMICS IN POTATO PRODUCTION SYSTEMS

Concern over undesirable environmental impacts and low profitability o f conventional potato (Solanum tuberosum L.) production systems has le d to efforts to reduce agrichemical use while improving yield and net returns. Weed management based on a better understanding of weed respo nses to tillage and other cropping practices is a key to success in th ese efforts. We conducted a 4-yr field experiment on a Caribou gravell y loam (coarse-loamy, mixed, frigid Typic Haplorthods) in Presque Isle , ME, in which potato was grown in alternating years with either oat ( Avena sativa L.) or berseem clover (Trifolium alexandrinum L.), in plo ts that were either moldboard plowed (MP) or chisel plowed (CP). To de termine yield losses due to weed interference, potato was grown either in weed-free conditions or with weeds that survived cultivation and b illing. Seed density, plant density, and biomass of dominant weed spec ies (Chenopodium album L. and Brassica and Raphanus spp.) were lower f ollowing MP than CP. Average loss of U.S. No. 1 tubers due to weed int erference was 12% with MP, compared with 43% with CP. Weed and potato responses to rotation crops differed between years. Weed biomass produ ction was lower in oat than in berseem clover during the 1990 rotation crop phase. In the subsequent 1991 potato crop, yield loss due to wee d infestation was 13% following oat, compared with 38% following berse em clover No difference in weed growth was evident between oat and clo ver rotation crops in 1992, and there were no rotation crop effects on weed-related yield loss in the subsequent 1993 potato crop. me presen t a conceptual model that incorporates these data, links need life sta ges and crop performance, and illustrates the effects of interference between weed species. The model suggests that, if need growth in rotat ion crops can be strongly suppressed, chisel plowing should result in low densities of annual weed species and minimal yield loss in subsequ ent potato crops.