What is the best row spacing for soybeans: 7.5, 10, 15, 20 or 30 inches?
That is a question I got one morning in April. My short answer was: it depends. I have been tracking row spacing and yield on soybeans for 15 years now and my conclusion is that soybeans can yield similarly regardless of row spacing and narrow rows don’t always outyield wider rows.
Today row spacing for soybeans seems to be driven by the row spacing for corn. If you plant corn in 30-inch rows you will plant soybeans in 30-inch rows. If you plant corn in 20-inch rows soybeans will be planted in 20-inch rows. However, there are farmers who still hold on to their 15-inch split planters for planting corn and soybeans. Fortunately, drills are rarely used today to plant soybeans because seed rate is very high (200,000+), and emergence is quite uneven.
Dr. Emerson Nafziger, long-term field researcher in Illinois, compared 15-inch and 30-inch rowed soybeans. He concluded that soybean yields were significantly higher in 15-inch rows across 20 trials, were significantly lower in only one trial and showed no significant difference in 19 trials. Nafziger said “Overall, the difference (2.1-bushel advantage to 15-inch rows) is statistically significant, as indicated by the descriptive statistics.”
Nafziger’s results confirm what most of us believe – that narrow rows win out about half the time.
Dr. Fred Below’s Six Secrets work in Illinois (2013 to 2017) showed that in a low-tech standard system, there was a 4 to 5 bu/A gain when soybeans were planted in 20-inch rows compared to 30-inch rows. However, in a high-tech management system, planting in 20-inch rows showed an 8 to 9 bu/A gain over 30-inch rows. So, if you are deploying a high-tech system with all the bells and whistles and planting early, you will get a bigger yield response planting in narrow rows.
Personally, I think the evidence is clear that 5 – 7 years out of 10, narrow row beans will outyield beans planted in 30-inch rows. But then again in 3 or 4 years 30-inch bean will yield the same or perhaps higher. Thus, you can see that sometimes it is difficult to believe which row spacing is better.
The earlier you plant beans the less likely you will see a consistent benefit and the later you plant soybeans the more likely you will benefit. If you plant from mid-April to mid-May, narrow rows won’t always win out over thirties. From mid-May to mid-June narrow rows will probably win out. And after mid-June and into July (double-cropped beans) narrow rows always win out.
Narrow row beans pay off more times than not, but having separate planters for corn and beans probably doesn’t pay today. Maybe 20-inch spacing is the answer. I believe the future for corn is 20-inches and it is a good spacing for soybeans, too. I would put moving to narrow-row beans high on your management list. Certainly, buying into some way to narrow rows to no more than 20 inches should become an important consideration