Narrow Row Spacing
Crop competition is key to good weed control, with a dense crop canopy capable of suppressing weeds for most of the growing season. Weed seedlings require sunlight to 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 grow 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 shading of area between crop rows. Research in soybean has shown that row spacing of 15 inches or less achieves faster canopy closure than 30 inch rows. Research in North Carolina demonstrated that late-season weed emergence was lower in 18 and 9 inch row spacing than 36 inch rows 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. Similar benefits of narrower rows for weed control have been observed in grain sorghum. Palmer amaranth biomass was reduced 33% with 7 and 15 inches rows compared to 30 inches rows.
Planting cotton in narrower rows (less than 20 inches) does increase the competitiveness with weeds, yet there are agronomic considerations that prevent planting in rows narrower than 30 inches. Cotton harvesting and lint quality are two of these considerations.
Benefits of narrow row spacing in corn have been more variable than soybeans or sorghum. Late season weed control in corn 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.
- Knezevic SA, Evans SP, Mainz M (2017) Row spacing influences the critical timing for weed removal in soybean. Weed Technology 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.
- Bradley KW (2006) A review of the effects of row spacing on weed management in corn and soybean. Crop Management 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 Technology 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 Technology 29:390-404.
- Dr. Kurt Vollmer, University of Maryland
- Victoria Ackroyd
- Claudio Rubione
- Mark VanGessel