Influence of integrated agronomic and weed management practices on soybean canopy development and yield

The role of weed suppression by the cultivated crop is often overlooked in annual row cropping systems. Agronomic practices such as planting time, row spacing, tillage and herbicide selection may influence the time of crop canopy closure. The objective of this research was to evaluate the influence of the aforementioned agronomic practices and their interaction with the adoption of an effective preemergence (PRE) soil residual herbicide program on soybean canopy closure and yield. A field experiment was conducted in 2019 and 2020 in Arlington, WI, as a 2x2x2x2 factorial in a randomized complete block design, including early (late April) and standard (late May) planting time, narrow (38 cm) and wide (76 cm) row spacing, conventional tillage and no-till, and soil-applied PRE herbicide (yes and no; flumioxazin 150 g ai ha(-1) + metribuzin 449 g ai ha(-1) + pyroxasulfone 190 g ai ha(-1)). All plots were maintained weed-free throughout the growing season. In both years, early planted soybeans reached 90% green canopy cover (T-90) before (7 to 9 d difference) and yielded more (188 to 902 kg ha(-1) difference) than the standard planted soybeans. Narrow-row soybeans reached T-90 earlier than wide-row soybeans (4 to 7 d difference), but yield was similar between row spacing treatments. Conventional tillage resulted in a higher yield compared to a no-till system (377 kg ha(-1) difference). The PRE herbicide slightly delayed T-90 (4 d or less) but had no impact on yield. All practices investigated herein influenced the time of soybean canopy closure but only planting time and tillage impacted yield. Planting soybeans earlier and reducing their row spacing expedites the time to canopy closure. The potential delay in canopy development and yield loss if soybeans are allowed to compete with weeds early in the season would likely outweigh the slight delay in canopy development by an effective PRE herbicide.

Automated summary

The role of weed suppression by the cultivated crop is often overlooked in annual row cropping systems. Agronomic practices such as planting time, row spacing, tillage, and herbicide selection can influence crop canopy closure and yield. Early planting and narrow-row soybeans expedite canopy closure, while conventional tillage improves yield.