Assessing the trends of soil weed seed bank in conservation agriculture systems

This net-house experiment was conducted at the Department of Agronomy, Bangladesh Agricultural University, Mymensingh, Bangladesh, during January-December 2016. Soil samplings were done at 0-15 cm soil depth from four locations viz., Mymensingh, Durgapur, Godagari, and Baliakandi areas of Bangladesh after the end of conservation agriculture (CA) trials in each site. At Mymensingh, CA, tests were conducted at the soil science field laboratory during 2012-2015. Here T. aman (summer) rice, wheat, and mungbean were grown using conventional tillage (CT), and strip tillage (ST) retained with 20 and 40% residues of the previous crop. At Durgapur and Godagari, on-farm CT and ST were practiced kept 20 and 50% residues of the earlier crop during 2010-2015. At Durgapur, the cropping pattern was T. aman rice-mustard-boro (winter) rice and jute-lentil-mungbean while at Godagari, the cropping pattern was T. aman rice-wheat-mungbean and jute-chickpea-mungbean. At Baliakandi, T. aman rice, wheat, and jute were grown on-farm during 2012-2015 following CT, ST, bed planting (BP), and Zero tillage (ZT) retained 20 and 50% residues. Collected five soil samples from each plot of each site that is a total of 290 soil samples from four trial sites were bulked and placed in individual trays following a completely randomized design with four replications. The headcount of weed was continued during the entire time of experimentation. The experimental data revealed that, in terms of weed species composition and weed density, the smallest size weed seed bank was found in long-term ST, followed by CT, BP, and ZT. On the other hand, smaller sized weed seed bank composition was found in 40 or 50% crop residues than 20% residues. The higher number of perennials weeds than annual weeds was recorded in ST, BP, and ZT, but the reverse was in CT. Based on the results, it could be concluded that ST with the retention of 40-50% residues of previous crops facilitate lesser weeds but favors perennial weeds compared to conventional tillage. Weed reduction in strip tillage is even higher than BP and ZT.