Weed seed bank and dynamics in wheat as affected by sowing time and rice residue management methods

Field studies were carried out to evaluate the effect of sowing time and residue management methods of preceding rice varieties (with different residue load) on weed seed bank and density in wheat during Rabi 2019-20 and 2020-21 in Punjab. Experiment was conducted in split plot design keeping combinations of 2 preceding rice varieties with different residue loads and 2 sowing times in main plots and 4 residue management methods in sub-plots with 3 replications. Results revealed that weed population and biomass at 30 days after sowing was higher in fields with low residue load (6.96-7.89 t/ha of PR 126) as compared to high residue load (10.25-11.44 t/ha of PR 122). Population and biomass of Medicago denticulata was lower in 15^th November sown wheat in contrast to other broad-leaf weeds. Lower density of Phalaris minor was recorded under early sown wheat (25^th October). Weed density and biomass was lower under happy seeder as compared to other residue management methods. In mould board plough + rotavator treatment, weed seed per unit area was lower in 0-5 cm soil layer but it was higher at 10-15 cm soil depth as compared to other residue management methods. Crop growth parameters (plant height, tillers density and biomass) were not influenced by rice residue load and wheat planting time. Grain yield was recorded highest under early sown wheat as compared to late sown wheat. Grain yield was recorded highest under Happy Seeder as compared to other residue management system during second year. However, grain yield was recorded similar under all residue management methods during first year. The results suggested that grass weeds were less in 25^th October sown wheat but 15^th November sown crop has less broad-leaf weeds.