Crop performance, nutrient uptake vis-a-vis weed suppressive ability of mechanically transplanted rice (Oryza sativa) as influenced by age of seedlings and planting density

An experiment was conducted during the rainy season of 2010 and 2011 at Punjab Agricultural University, Ludhiana to investigate the effect of seedling age and planting densities on crop performance and weed-suppressive ability of mechanically transplanted rice (Oryza sativa L.). The experiment comprising seedlings of 3, 4 and 5 weeks age and planting densities of 30 cm × 12 cm, 30 cm × 14 cm and 30 cm × 16 cm, was conducted in a factorial randomized block design with 4 replications. Mechanical transplanting of 3 weeks old seedlings showed superiority in terms of plant height, dry-matter accumulation and number of tillers to 4 and 5 weeks old seedlings when recorded at different growth stages. Transplanting of 3 and 4 weeks old seedlings were equally effective in their weed suppressive ability and certainly better than 5 weeks old seedlings, as dry-weight of weeds was significantly lesser than that in 5 weeks old seedlings. Leaf area-index (LAI) and photosynthetically active radiation (PAR) interception recorded at panicle-emergence stage, which were statistically at par in 3 and 4 weeks old seedlings but significantly higher than that in 5 weeks old seedlings. Mechanical transplanting of 3 and 4 weeks old seedlings recorded significantly higher N, P and K uptake than that in 5 weeks old ones. The planting density of 30 cm × 12 cm recorded significantly higher LAI, PAR interception, yield-attributing characters, grain yield and N, P and K uptake than that in 30 cm × 14 cm and 30 cm × 16 cm. Planting density of 30 cm × 12 cm proved to be optimum spacing for mechanically transplanted rice, as it gave 4.7 and 12.2% higher grain yield over the 30 cm × 14 cm and 30 cm × 16 cm spacing respectively. It also proved to be significantly better for weed-suppressive ability, as it recorded reduction in dry-matter of weeds to the tune of 8.6–26.5% and 17.1–37.3% over 30 cm × 14 cm and 30 cm × 16 cm respectively, at different growth stages.