Effect of crop-weed competition on yield and nutrient uptake by direct-seeded rice (Oryza sativa) in rainfed, lowland situation

A field experiment was conducted during wet season of 1995 and 1996 to stud y the effect of crop-weed competition on weed growth, yield, and nutrient u ptake by direct-seeded rice (Oryza sativa L.). Initial weed-free for 45 day s or longer, and weedy up to 15 days after sowing resulted significantly hi gher rice grain and straw yields, and lower dry weight and nutrient uptake by weeds during both the years. Weed infestation for first 15 days caused n o significant loss in grain yield compared to weed-free for 45 or 60 days a fter sowing. The season-long weedy crop resulted 57% reduction in grain yie ld compared to season-long weed-free. Initial weed-free for first 30 days c aused 25% reduction in grain yield which was higher than loss caused by ini tially weedy for 30 days (22%). The uptake of nutrients (NPK) by rice crop was significantly higher in weed-free treatment. The season-long weedy depl eted 35 N, 15 P2O5 and 45, K2O kg/ha by weeds while rice crop under weed-fr ee up to maturity removed 60, 26 and 80 kg/ha of N, P2O5 and K2O respective ly.