Narrow Row Spacing
Crop competition is key to good weed control, and a thick dense crop canopy will serve to suppress weeds for most of the growing season. Each seedling requires a certain amount of light to germinate and grow, and quickly establishing a thick crop canopy can greatly reduce the amount of sunlight available. Horseweed is a good example of a weed that does not do well under a thick crop canopy, as it is very small seeded (has little stored energy) and thus must quickly start photosynthesis or perish. A dense, healthy crop may also outcompete weeds for other resources like water and nutrients.
Narrow row spacing can allow for faster canopy development. Research in soybean has shown that row spacing of 15 inches or less achieves faster canopy closure. As a result, late season weed control is frequently better with narrow row spacing. Moreover, studies have reported up to a 20% increase in soybean yield with narrow row spacing compared to wide row spacing when combined with good weed management practices.
While narrow row spacing improves weed control in soybeans, results in corn have been more variable. Late season weed control is often similar, regardless of row spacing. Using additional weed management tactics prior to corn canopy closure will decrease the possibility of weed resurgence later in the growing season.
- Corn planted in 15 inch rows closed canopy one week earlier than corn planted in 30 inch rows, and reduced total weed cover (Teasdale 1995).
- Late season weed resurgence in soybean was lower as row spacing decreased from 36 inches (43 to 86%) to 18 inches (57%) to 9 inches (94%) (Yelverton and Coble 1991).
- In sorghum, Palmer amaranth biomass was reduced 33% with 7 and 15 inches rows compared to 30 inches rows (Besancon et al. 2017)
- A study in Australia found that soybean yield was greater and Rhodes grass biomass was less when soybean was planted in 10 inches rows compared to 30 inches rows.
- Knezevic SA, Evans SP, Mainz M (2017) Row spacing influences the critical timing for weed removal in soybean. Weed Technol 17:666-673.
- Licht M (2018) Consider 15-inch row spacing in soybean. https://crops.extension.iastate.edu/cropnews/2018/02/consider-15-inch-row-spacing-soybean.
- Linsey L (2016) 3 Planting factors for best soybean yields. https://www.no-tillfarmer.com/articles/5663-planting-factors-for-best-soybean-yields.
- Bradley KW (2006) A review of the effects of row spacing on weed management in corn and soybean. Crop Manag Online at doi:10.1094/CM-2006-0227-02-RV
- Harder DB, Sprague CL, Renner KA (2007) Effect of soybean row width and population on weeds, crop yield, and economic return. Weed Technol 21:744-752
- Bell, H.D., J.K. Norsworthy, R.C. Scott, and M. Popp. 2015. Effect of row spacing, seeding rate, and herbicide program in glufosinate-resistant soybean on Palmer amaranth management. Weed Technol. 29:390-404.
Credits: Dr. Kurt Vollmer, University of Delaware
Edits: Victoria Ackroyd, USDA-ARS Beltsville
Pictures: Claudio Rubione, University of Delaware