Soil fertility and disturbance can potentially modify weed dynamics in a corn–soybean rotation. Knowing how added mineral fertilizers and tillage influence weed populations in the long term can provide insight into weed community shifts, which may affect future weed management requirements. The first objective of this study was to evaluate the effect of 24 to 25 years of nitrogen and phosphorus fertilization treatments and tillage (moldboard vs. no-till) on weeds (density, biomass, and composition) before and after herbicide applications in 2016/corn and 2017/soybean. The second objective was to evaluate the effect of the same treatments 6 yr after no postemergence weed management in 2022/corn. Since the last evaluation performed in 2004, weed density, richness, and diversity increased, and more annual grasses were observed under both tillage regimes. No fertilization effect was observed on any weed variables, including composition, except for increased biomass when left to grow all season after crop planting. In managed plots, the density and biomass of annuals and perennials were generally higher in no-till, and discrepancies were highest for annual grass densities before herbicide application. Weed species richness and diversity based on counts were equivalent between tillage regimes, but total biomass was distributed between more species in no-till. Higher weed densities and concurrent weed biomass, observed in no-till, reduced crop yields in 2016/soybean only. The combination of low crop diversity and low use of residual herbicides during the trial potentially led to the observed species shifts and increased weed density.

Multilocational characterization of selected herbaceous and shrub legumes was carried out over a 3-yr period at lowland and midlatitude sites in the moist savanna agroecological zone in Nigeria where a south–north gradient exists for rainfall, length of growing season, and insolation. One study site each was located in coastal–derived savanna (DS), southern Guinea savanna (SGS), and northern Guinea savanna (NGS). A fourth site was located in the plateau of the NGS. Only one legume cover crop, lablab, produced adequate ground cover and good weed suppression in three locations irrespective of rainfall amount, duration, and distribution. Velvetbean was superior to other legume cover crops in the lowland savanna locations where rainfall exceeded 1,100 mm/yr but not in the plateau of the NGS where rainfall was less than 1,000 mm. Pigeonpea grew luxuriantly and produced canopy cover that effectively suppressed weeds in the DS where rainfall was high. Centurion grew well and suppressed weeds effectively only in the SGS site where rainfall of 1,120 mm was well distributed over a 5-mo period. Sunnhemp grew well and suppressed weeds only in the NGS study sites where rainfall duration was 4 mo and the length of the growing period was short. Weed density was negatively correlated (P < 0.05) with percentage ground cover of those legume cover crops that were effective in weed suppression in all locations. Redundancy analysis revealed significant associations between weed species and cover crops at each of the locations.

Management practices and cropping systems that serve as integrated weed management practices, and at the same time can contribute to improved soil quality, will be important for the sustainability of agricultural production systems. The objective of this study was to assess weed species population density under contrasting tillage (conventional tillage [CT] and no tillage [NT]), residue burning (burn and no burn), and residue level (low and high) treatments after 5 and 6 yr of consistent management in a wheat–soybean double-crop production system. A field experiment was conducted from fall 2001 to fall 2007 in the Mississippi River Delta region of eastern Arkansas on a Calloway silt–loam. Weed assessments were conducted twice during the soybean growing season, before (early season) and after herbicide application (late season) in 2006 and 2007. Total weed density was greater under CT (513 plants m−2) than under NT (340 plants m−2) early in the growing season in 2006, but was greater under NT than CT late in the season in 2007, suggesting that the effectiveness of glyphosate on total weeds differs between CT and NT. Averaged across residue levels, grass species density was greatest in the NT–burn (68 to 167 plants m−2) combination and lowest in the NT–no-burn (41 to 63 plants m−2) early in the growing season in both years. Broadleaf density was greater early (200 to 349 plants m−2) than late (18 to 20 plants m−2) in the growing season under both CT and NT in 2006, but in 2007 broadleaf density did not differ by tillage treatment between seasons. Perennial weed density was greater in the burn (99 plants m−2) than in the no-burn (59 plants m−2) treatment in 2006. No tillage, no burning, and a high residue level appeared to contribute to the suppression of most weed species without reducing herbicide efficiency.