EFFECT OF NITROGEN, PHOSPHORUS AND POTASSIUM ON WEED EMERGENCE AND SUBSEQUENT WEED COMMUNITIES IN SOUTH COASTAL BRITISH COLUMBIA

Abstract

The effect of fertilizer on weed emergence and subsequent weed communities was studied in a greenhouse and in the field. In greenhouse experiments, N at 100 kg ha−1 stimulated grass emergence but had no effect on broadleaf weeds. Emergence of broadleaf weeds was suppressed by 200 kg ha−1 and that of grasses by 300 kg ha−1. Emergence of cabbage (Brassica oleracea L.), carrot (Daucus carota L.) was suppressed by 100 kg N ha−1 while suppression of emergence of corn (Zea mays L.), wheat (Triticum sativum L.) and cucumber (Cucumis sativus L.) was less pronounced. In field experiments, N applied in early April increased the number of corn spurry (Spergula arvensis L.) seedlings. After several weeks, lady’s-thumb (Polygonum persicara L.) assumed biomass dominance in 1986 while lamb’s-quarters (Chenopodium album L.) was dominant in 1987 and 1988 on plots that received N. Corn spurry was the dominant weed in number and biomass on plots with no N. When fertilizer was applied in late May, a number of weed species emerged evenly across the various treatments; however, towards maturity, lamb’s-quarters dominated in amount of biomass where N was applied, while corn spurry and shepherd’s-purse (Capsella bursa-pastoris L.) dominated the plots with no N. Phosphorus had a small effect and K had no effect on weed communities and there were no significant interactions. When different rates of fertilizer were tested, emergence of corn spurry was stimulated by 100 kg N ha−1 but was suppressed by higher rates. Results from these experiments have demonstrated that weed emergence and subsequent weed communities in south coastal British Columbia can be greatly altered by fertilizer.Key words: Fertilizer, nitrogen, phosphorus, potassium, weed emergence, weed communities