Residual effects of herbicides on weed interference and productivity in wheat (Triticum aestivum) under a conservation agriculture-based onion (Allium cepa)-wheat cropping system

A field experiment was conducted during the rainy (kharif) and winter (rabi) seasons of 2015-16 and 2016-17 at the ICAR-Indian Agricultural Research Institute, New Delhi, to evaluate the effects of conservation agriculture (CA) and carryover weed management on weed interference and crop productivity of wheat [Triticum aestivum (L.) emend Fiori & Poal] in an onion (Allium cepa L.)-wheat system. Three conventional and conservation tillage and 7 weed-management treatments were laid out in a split-plot design, with 3 replications. The CA-based zero-till raised-bed system with residue retention (ZTRB + R) resulted in significant reduction in total weed density and biomass compared to conventional till flat bed (CTFB), which led to higher weed control efficiency (11%), grain (4.02 t/ha) and straw yield (4.24 t/ha), and net returns 46000 /ha in the year 2016-17. The zero-till flat bed with residue (ZTFB + R) and ZTRB + R led to an increase in wheat grain yield by 5.1 and 3.6%, and net returns by 28 and 18% than CTFB respectively. Among the herbicidal treatments, the pendimethalin followed by (fb) ethoxysulfuron resulted in the highest reduction in weed density (29 and 34%) and weed dry weight (55 and 56%) in both years, and the pendimethalin fb quizalofop was comparable with it in these regards. The pendimethalin fb quizalofop- or ethoxysulfuron- treated plots provided higher wheat grain yield (4.24 t/ha), net returns 49000 /ha and net benefit: cost (B: C) in the year 2016-17. The pendimethalin fb ethoxysulfuron had higher residual effect on weeds in wheat but inflicted severe phytotoxicity to onion in previous season that reduced onion yield significantly. Therefore, the pendimethalin fb quizalofop application to onion is most preferred considering onion and wheat crops safety and may be adopted under zero-till raised-bed for higher productivity and profitability in onion-wheat cropping system.