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Dr. Dan Talks Agronomy
Friday, August 15, 2014 10:59AM CDT

By Dan Davidson
DTN Contributing Agronomist

Will this be the year that more farmers hit 100-bushel soybeans on a field scale? We know it can be done with attention to detail and the right weather. Three Arkansas growers achieved the 100-bushel mark in yield contests last year. Numerous Brazilian growers have broken the 100-bushel-per-acre threshold in yield challenges over the past few years. Then there's Missouri farmer Kip Cullers' national yield record of 160 bushels per acre set in 2010.

In early July, I wrote an article about how some fields of soybeans were struggling with uneven emergence, slow growth and signs of a yellowish hue after heavy June rains. The reduced growth and yellowing suggested that nitrogen fixation was reduced at the same time that residual nitrate leached below the root zone, limiting nitrogen to the plant. July turned out to be a drier month with moderate temperatures and vegetative growth recovered.

The question remains: Will the symptoms seen in June affect soybean yield at harvest? What we know is soybeans are good at compensating for periods of stress. We also know excessive vegetative growth in August don't always deliver yield.

Last week I walked a few soybean fields in central Illinois and was astonished by the health of the crop, height of the crop and pod set and yield potential. Soybeans are now R5 or R6 stage. Flowering is over, final number of pods on the main stem and branches are mostly set and pods are filling. Some of those small pods at the top of the plant won't survive and set a seed. The only remaining detail is seed size and weight. If the weather continues to be moderate and moist and we have a moderate, warm September, soybeans should finish off with a flourish.

The three Arkansas producers who broke 100 bushels in 2013 did so by practicing good management and irrigating, but they also experienced very good weather with mild temperatures. None of them went out of their way to spray on multiple products at multiple times during the season to feed the crop and protect it against the threats of nature. They did all spray a fungicide to protect against foliar disease pressure, which is a common practice in Arkansas.

One commonality across the soybean belt this year (with a few exceptions of regions hit by excess rainfall) is the crop has not been overly stressed by the weather, and disease pressure has been minimal. Soybean aphids and white mold also like this kind of weather. Aphid outbreaks are occurring and without control, they can significantly reduce yield quickly.

In a season like this, one of the things we see in soybeans that are well managed and grown under high fertility is that beans will get rank, or tall with excessive amounts of leaf material. Rank beans will lodge and experience yield loss and harvest difficulties. Excessive vegetative growth in soybeans does not necessarily translate into yield -- the plant puts too much energy and resources into developing and support of vegetative growth instead of setting and filling pods. This might be the year to do an R5 foliar application of nutrients just to get the plant enough energy to fill out all the pods it has acquired.

My recommendation: Get out and walk your fields. If your soybeans are about 3 feet tall, you have no worries. If your soybeans are 4 to 5 feet tall when you hold them upright with your hand, you probably have excessive growth and soybeans could lodge. You might want to consider in the future how to keep your beans a bit shorter in stature. One strategy some growers follow is dinging the growing point at the top of the plant to reduce its height while increasing branching. This can be done at V3 to V4 stage using Cobra herbicide, rolling small soybean plants and/or using a growth regulator cocktail. Keep in mind that the data is not always clear on how beneficial it is to beat up your beans.

If you are getting curious where your yields might be going this season, count pods on a number of average-looking plants. The average soybean plant will have 40 to 60 pods and produce about 40 to 60 bushels. While pod counts aren't a reliable way to estimate yield, as a general rule of thumb, I have found that pod count does seem to correlate roughly with yield range. When I visited Cullers' plots in 2006 and 2007 when he produced 139 and 156 bushels, I counted pods per plant and had counts of 140 to 160 pods, fairly close to his contest yields.

In spite of the rough start for soybeans, 2014 will be the year for soybeans to set some yield records. However, we still need some rain in August and frost to hold off to complete the job.

Dan Davidson can be reached at AskDrDan@dtn.com

Follow Dan Davidson on Twitter @dandavidsondtn

(PS/AG)


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