Weed seedbank as influenced by tillage and herbicide in direct seeded rice‐mustard cropping sequence in lateritic soil of eastern India

Abstract

The above‐ground community dynamics of weeds represent the soil weed seedbank in an agro‐ecosystem. Hence, understanding the seedbank will offer an idea for future weed management tactics. We aimed to determine the density of weed seedbank and emergence of major weeds in direct seeded rice (DSR) (Oryza sativa L.)—mustard (Brassica campestris L. var. yellow sarson) cropping sequence under varied tillage and herbicide combinations. The present study on weed seedbank was conducted using seedling emergence method after collecting the soils at the harvest of mustard at the completion of 2 years field experimentation. The experiment was conducted in split‐plot design with two tillage practices [zero tillage (ZT) and conventional tillage (CT)] in main plot and eight weed management practices in DSR [oxadiargyl followed by (fb) bispyribac‐sodium, penoxsulam + cyhalofop‐butyl, oxadiargyl fb penoxsulam + cyhalofop‐butyl, fenoxaprop‐p‐ethyl + ethoxysulfuron, oxadiargyl fb fenoxaprop‐p‐ethyl + ethoxysulfuron, pendimethalin fb bispyribac‐sodium, unweeded control, and weed free check] as subplot. The carry‐over effect of tillage and weed management practices were recorded in mustard crop. Seed emergence study revealed that ZT reduced the emergence of grassy weeds (by 13.7%) and total weed emergence (19.5%) in comparison to the CT (p < 0.05). However, emergence of broadleaf weeds was 24.5% higher in ZT than in CT. The higher infestation was recorded for Ludwigia parviflora (Jacq.) Raven under penoxsulam + cyhalofop‐butyl, fenoxaprop‐p‐ethyl + ethoxysulfuron, Cyperus iria (L.) under fenoxaprop‐p‐ethyl + ethoxysulfuron, and Eleusine indica (L.) Gaertn. under pendimethalin fb bispyribac‐sodium, oxadiargyl fb bispyribac‐sodium. Sole application of post‐emergence (POE) herbicide decreased the total weed emergence by 22.2%–28.1% than unweeded control (p < 0.05). Whereas, sequential application of PRE + POE herbicides decreased the total weed emergence by 32.8%–36.9% than unweeded control (p < 0.05). Notably, sedge weeds such as Cyperus iria (L.) and Fimbristylis miliacea (L.) Vahl were lower in ZT than in CT under herbicide treated plots (by 66.6%–84.3%) than unweeded control. Thus, ZT with oxadiargyl 90 g a.i. ha−1 fb fenoxaprop‐p‐ethyl + ethoxysulfuron (90 + 15 g a.i. ha−1) as tank‐mix can be effectively used to lower the weed seedbank density vis‐à‐vis managing complex weed flora in DSR and rice‐mustard cropping sequence.