Weed spectrum in different wheat-based cropping systems under conservation and conventional tillage practices in Punjab, Pakistan

Excessive tillage in conventional agriculture has led to soil and environmental degradation. Conservation agriculture (CA) has evolved as an alternate and sustainable crop production system. However, weed control is a serious issue in CA; nonetheless, allelopathy offers a viable option for weed management. This study was conducted to evaluate the shift in weed spectra in different wheat-based cropping systems under different tillage practices in Punjab, Pakistan. Wheat was planted in fallow-wheat, rice-wheat, cotton-wheat, mungbean-wheat and sorghum-wheat cropping systems with zero tillage (ZT), conventional tillage (CT), deep tillage (DT) and CT with beds sowing (BS; 60/30 and 90/45). The most important weeds identified were fat hen, common goosefoot, horseweed, garden spurge, broad-leaved dock, yellow sweet clover, false daisy, salt marsh, rabbit foot grass, bermuda grass, red sprangletop, corn spurry and littleseed canarygrass. Maximum diversity of weeds (number of weed species) was recorded in cotton-wheat under ZT; whereas the sorghum-wheat system had minimum diversity of weeds under DT. Fallow-wheat and mungbean-wheat systems had more grassy and broad leaf weeds, respectively, while sorghum-wheat had less density of these weeds. Likewise, ZT had higher while DT and BS had less density of grassy and broad leaf weeds. However, CT favored some broad leaf weeds like fat hen and common goose foot; DT stimulated only common goose foot; whereas ZT supported some broad leaf and all grassy weeds. Sorghum-wheat system suppressed most of the weeds, grasses in particular, and three grassy weeds (salt marsh, bermuda grass and red sprangletop) were absent owing to its strong allelopathic potential; however, this system favored littleseed canarygrass under ZT. In conclusion, divergent wheat-based cropping systems had different weeds spectra under different tillage practices; and choice of cropping sequence may help suppressing weeds. Inclusion of allelopathic crops, like sorghum, in the wheat-based cropping system may help managing weeds under conventional and conservation tillage practices. (C) 2016 Elsevier B.V. All rights reserved.