Soybean Row Spacing—An Overlooked Practice in the Weed Control Toolbox

Holly Thrasher

May 27, 2020

When we talk about the fight against weeds in your soybean fields, herbicides and seeds with herbicide tolerance are often the first things that come to mind. 

Over the years, the development of soybeans with tolerance to glyphosate, glufosinate, dicamba and 2,4-D have made a huge impact on the way we farm, adding more options to the weed control toolbox from which farmers can work.

But herbicides aren’t your only option for keeping your soybean fields clean.

Row spacing can play a significant role in your in-season weed control program.

Farmers today utilize a variety of row spacings when planting soybeans, ranging from 7.5 to 38 inches. Those wider row spacings leave a lot of open area between the plants that the canopy eventually has to cover to block weeds from the sunlight they need to grow. 

In fact, canopy closure typically happens 15 days sooner in 15-inch rows than it does in 30-inch rows—that’s two fewer weeks that weeds have to develop in your fields!

The faster you can shade out the weeds, the less dependent you are on herbicides. This is especially important when timing or weather becomes an issue. 

Another big plus of this agronomic practice is that narrower rows can more efficiently intercept light. And since light is what drives dry matter production, some farmers have seen an increase of 3-4 bushels per acre in their narrower row setups. 

But narrow rows may not be right for everyone. If your equipment isn’t set up for narrow rows, then you may not be ready to take on new or unexpected operating costs. A thicker canopy can also make certain diseases, such as white mold, more difficult to control. 

PRO-TIP: If white mold is a concern, lowering plant populations can allow more airflow through the canopy and make your soybean crop less conducive to development of the disease. 

There are many tools available to keep soybeans clean throughout the growing season. Starting clean is key in the fight for weed-free fields, but herbicide sprays, row spacing and, in some areas, conventional tillage are all methods you can use to limit weed competition all year long. 

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Sources:

1. https://crops.extension.iastate.edu/soybean/production_spacing.html

2. https://crops.extension.iastate.edu/cropnews/2018/02/consider-15-inch-row-spacing-soybean

3. https://webapp.agron.ksu.edu/agr_social/eu_article.throck?article_id=1806

Holly Thrasher

May 27, 2020