Weed populations of intensive rice based cropping system as affected by tillage and increased crop residues in Bangladesh

Abstract

When farmers first shift from conventional tillage (CT) to conservation agriculture (CA), weeds control may be more difficult due to the absence of tillage. However, in the longer term (3-5 years), CA changes to weed dynamics may alter the weed seedbank. The nature of weed seedbank changes over time in intensively cropped rice-based rotations typical of the Eastern Gangetic Plain of Bangladesh is not well understood. Three long term CA experiments were sampled (at Rajbari after three years and Rajshahi after five years) for effects of decreased soil disturbance strip planting (SP) and bed planting (BP) at both sites and Zero tillage (ZT) at Rajbari, increased retention of standing residues of previous crops (20 vs. 50%. The weed seedbank in 0-15 cm soil was quantified by assessing emergence from trays in a net-house experiment during January-December 2016. The year-round count of emerged weeds revealed the fewest number of weed species (especially broadleaf weeds) and lowest weed density in SP, followed by CT, BP, and ZT with 50% crop residues. The SP, BP, and ZT produced a higher number of perennials weeds than annual weeds, which was the opposite of CT. The continuous practice of SP and increased crop residue retention for three or more years decreased the size of weed seedbank but increased the relative proliferation of perennial weeds compared to CT. Weed seedbank size in SP was even smaller than BP and ZT.