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Purple Nutsedge (Cyperus rotundus) is difficult to manage and persists in onion (Allium cepa) fields of the tropics. Critical period of weed control can be highly influenced by Nitrogen fertilizer (N) application. Thus, determine the critical period of purple nutsedge control in onion for different levels of nitrogen fertilizer is useful in making decisions on the need for and timing of purple nutsedge control in both biological and economic perspectives. A field study was conducted from June – September, 2010 in Sri Lanka to evaluate the influence of nitrogen application on the critical period of purple nutsedge control in onion. Nitrogen fertilizer was applied at rates equivalent to 100, 150, and 200 kgha-1. A quantitativeseries of treatments of both increasing duration of purple nutsedge interference and length of weed-free period were imposed within the different rates of N. The beginning and end of the critical period of purple nutsedge control based on 5% acceptable yield loss level were determined by fitting logistic and Gompertz equations to relative yield data representing increasing durations of purple nutsedge interference and weed-free period, respectively. The beginning of the critical period of the purple nutsedge control for onion varied with N application rate. The addition of N hastens the end of the critical period of the purple nutsedge control. Critical period of purple nutsedge control for onion reduced with increasing N. Plant height, dry weight and bulb diameter were significantly (P<0.05) influenced by interaction effect of purple nutsedge infestation period and Nitrogen application rate. In addition, Nitrogen application rates and duration of weed free period significantly (P<0.05) interacted with onion height, dry weight and bulb diameter. Overall, this study revealed that reductions in nitrogen use may create the need for more intensive purple nutsedge management in onion fields in the minor seasons of the Batticaloa.

agrieast

Influence of nitrogen fertilizer and duration of Purple Nutsedge (<em>Cyperus rotundus</em>) interference on Onion (<em>Allium cepa</em>) growth and yield in minor seasons in Batticaloa, Sri Lanka

Influence of nitrogen fertilizer and duration of Purple Nutsedge (Cyperus rotundus) interference on Onion (Allium cepa) growth and yield in minor seasons in Batticaloa, Sri Lanka