SESBANIA KNOCKDOWN DAYS AND SEED RATES OF DRY DIRECT SEEDED RICE INFLUENCE WEED DYNAMICS AND PRODUCTIVITY OF RICE
In dry direct seeded rice (DDSR), weeds are the major problems limiting the productivity of crop. Sesbania co-culture with DDSR as well as seed rates of rice affect weed density by smothering effect on weeds and therefore can be a better weed management technique. Two year field experiments were conducted at Regional Agricultural Research Station, Parwanipur, Bara, Nepal from 2015 to 2016 to assess the effect of Sesbania knockdown dates and seed rates of DDSR on weed density and yield of rice. The experiment was arranged in two factorial strip plot design having four replications. The treatment comprised of four levels of seed rates of DDSR (25, 50, 75 and 100 kg ha-1) in the vertical strips whereas four levels of Sesbania knockdown days (21, 28, 35 and 42 days after sowing (DAS)) in horizontal strip. The data on weed densities, weed biomass, yield and yield attributing characters of rice were collected and analyzed using MSTATC statistical software. The data revealed decreasing weed density with increasing days of knockdown of Sesbania. Significantly lower weed densities were recorded when Sesbania was knockdown at 42 DAS as compared with 21 and 28 DAS at all dates of observations and in both years 2015 and 2016. The weed densities at knockdown days of 35 and 42 DAS were statistically at par with each other at 45 and 105 DAS in 2016. Similarly, weed densities were significantly lower when seed rates of DDSR was increased to 75 to 100 kg ha-1 as compared to 25 to 50 kg ha-1 in both years at most of observation dates. Sesbania knockdown at 42 DAS recorded significantly higher grain and straw yields but was statistically similar to knockdown dates of 35 DAS. Similarly, higher seed rates of 75 to 100 kg ha-1 produced better grain and straw yields than 25 to 50 kg ha-1 seed rates of DDSR. The higher yield of DDSR at knockdown of Sesbania at 35 to 42 DAS and higher seed rates of 75 to 100 kg ha-1 of DDSR was due to reduction in weed density which resulted in better yield attributes and grain yield of DDSR. Therefore, knockdown days of 35 DAS and seed rates of 75 kg ha-1 seem better option for DDSR.