Conservation tillage and weed management for improving productivity, nutrient uptake and profitability of soybean (Glycine max) grown after wheat (Triticum aestivum)

A field experiment was conducted during 2010 and 2011 at New Delhi to study the performance of soybean [Glycine max (L.) Merrill] grown after wheat [Triticum aestivum (L.) emend Fiori & Paol] under four tillage and crop establishment practices, viz. conventional tillage (CT)–flat-bed, CT–raised-bed, zero tillage (ZT)–flat-bed and ZT– raised-bed along with four weed management options, viz. unweeded control, pendimethalin @ 0.75 kg/ha as preemergence (PE) + hand weeding (HW), pendimethalin @ 0.75 kg/ha as PE + imazethapyr @ 75 g/ha as postemergence (POE), and wheat straw mulch @ 5 t/ha + imazethapyr @ 75 g/ha as POE. Total weed density and dry matter was comparatively higher under ZT than CT, but adoption of chemical + cultural weed control methods led to 79.5–82.5% weed control efficiency. Seed yield of soybean was equal under CT–raised-bed, CT–flat-bed and ZT–raised-bed, which was 11.7% more than ZT flat-bed. Similarly, pendimethalin + HW, pendimethalin + imazethapyr, and wheat straw mulch + imazethapyr resulted in almost similar weed control, and thus gave comparable seed yield, which was 39.1–42.7% higher than unweeded control. Weed and crop biomass followed opposite trends, and the seed yield decreased by 0.2 t/ha for an increase of 100 g/m² in weed dry weight. Concentration of N, P and K in seed and stover of soybean was not influenced but the uptake was highest under CT–raisedbed, which was on par with ZT–raised-bed. Nutrient uptake was highest under pendimethalin + HW, which was significantly higher than under pendimethalin + imazethapyr, and wheat straw mulch + imazethapyr. The highest net benefit:cost was under ZT–raised-bed and pendimethalin + imazethapyr or pendimethalin + HW, followed by CT–raised-bed under the same weed control treatments. It was concluded that soybean can be grown under permanent raised-bed with pre- and post-emergence herbicides for realizing higher productivity and profitability.