Effects of shading, relative growth rate and population density on weed responses to nitrogen management in corn

Abstract

Three experiments were conducted to identify mechanisms that might explain variations in weed responses to nitrogen (N) fertilization. The first experiment investigated the responses of two crop and six weed species to N fertilization rate and shading in a growth chamber environment. The dry weight and leaf area responses, among species, to N supply and shading were positively correlated with their maximum relative growth rates with the high N fertilization rate. Relative growth rates, among species, were negatively correlated with mean seed weights. The second experiment was conducted in field plots to investigate the effects of N fertilization timing and corn {Zea mays L.) population density on giant foxtail {Setaria faberi Herrm.), velvetleaf (Abutilon theophrasti Medicus), and common waterhemp (Amaranthus rudis Sauer) competition with com. Giant foxtail reduced com yield when no N fertilizer was applied until late June (POST N) but not when N fertilizer was applied prior to com emergence (PRE N). Velvetleaf seed yield was greater with the PRE N application than the POST N application, but giant foxtail seed yield was lower with PRE N than with POST N. The high corn population density reduced velvetleaf and giant foxtail seed yields, compared to the low com population density. Com, velvetleaf and giant foxtail seed yields were associated with their heights and light interception in mid-season. N fertilization timing and corn population density did not affect common waterhemp. A third experiment investigated the interactions between com and velvetleaf seedlings grown in a replacement series, as affected by N fertilization rate, in a glasshouse environment. N effects on seedling size of each species were positively correlated with the