When it comes to row spacing, it’s hard to know which option will result in the best yields for your crop. Especially since there are so many options to choose from, ranging from 7.5-inch rows all the way to 30 inches. So how do you pick the best option for your farm?
The current spacing of my soybeans is 15-inch rows. I believe there is a yield advantage with narrow rows as they achieve canopy closure faster and capture more light during the growing season. Quicker canopy closure also allows for greater shading of weed seedlings and reduces soil moisture loss through evaporation.
Benefits of 15-inch Rows
With this row spacing, I feel the plants receive enough sunlight for photosynthesis to take place to reach maximum yield potential. One of the drawbacks to narrow rows is that plants are pushed together, and the entire plant can’t capture as much sunlight. I feel 15-inch rows hit the sweet spot and allow plants to capture enough light to maximize yield.
Data available from over two decades of research proves consistently that narrower rows result in higher yields. Although, in most cases there is not much difference between 7.5, 10, 15, or 20-inch rows.
I used to use 30-inch rows and there is a large yield difference between the 30- and 15-inch rows. According to recent studies, there is an average yield advantage of 4.5 bu./acre. Using 30-inch rows allowed for more weeds to grow, and we aren’t very concerned about weeds since we started using 15-inch rows. (http://publications.iowa.gov/7965/1/RowSpacing.pdf)
I’ve tried 10-inch rows in the past and struggled with planting depth since we use a drill that does not have that precise of depth control. With our 15-inch spacing, we are using our planter that is able to give us more accurate depth and spacing. We have found that there is no real yield increase between 10- and 15-inch rows on our operation.
Concerns with Narrow Row Spacing
While there are several advantages to planting soybeans in narrow rows, it is always important to weigh your options. One of the main concerns with narrow row spacing is disease. However, you can achieve a higher yield with narrow rows if weeds and pathogens are managed properly. Diseases such as brown stem rot and soybean cyst nematode can reduce the yield benefit from narrow rows if you plant more susceptible varieties. If white mold seems to be an issue, plant those fields last and use low seeding rates when planting in 15-inch rows.
Many farmers also stick with wider rows because they are unwilling to invest in the right equipment. Split-row planter technology may allow for production of both corn and soybeans at the optimal row spacing, and also have more row units between the traditional 30-inch units that can be adjusted depending on the crop. This technology is more expensive, however the return on investment is high when you consider the 4.5 bu./acre yield advantage you get with 15-inch row soybeans.
Another concern you may have with narrow row spacing is a high seed cost and not being able to achieve a uniform stand. Current research conducted in Iowa suggests that a uniform harvest population of 100,000 plants/acre or more will maximize yield regardless of the row spacing. However, seeding rate decisions need to be considered based off the planting date, percent germ and field variability. If a drill or air seeder is used, higher seeding rates are unnecessary. Plant establishment is higher for narrow rows than wide rows, meaning that you will use a higher seeding rate to achieve the desired stand when using wide rows.
When it comes to harvest, it’s easier and more efficient to harvest soybeans in narrow rows than wide rows. Having a more even distribution of plants makes it easier to cut and feed them into the combine. Losses at harvest are reduced because there are no cultivator ridges to interfere with cutting height. Narrow row spacing can also be a risk management tool that helps stabilize yields in potentially stressful environments.
With the varieties we are using now, 15-inch rows seem to be the optimal width for our operation. As varieties change, we may consider adjusting our width as well.