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How Early Can (Should?) Soybeans Be Planted?

Today’s “conventional” soybean production system in the Midsouth is based on the Early Soybean Production System (ESPS), which is based on early planting of early-maturing soybean (MG IV–early MG V) varieties.

From experience and the vast volume of literature with which I am familiar, the optimum planting window for the ESPS in the Miss. Delta is April 10-20. Having said this, there has never been a set date for the earliest allowed planting in this system. Rather, this is usually dictated by the estimated last frost date for a given location in the region that generally favors the start of planting in the above optimum window. This is addressed in an article that appeared in the Feb. 10 2006 issue of Delta Farm Press and in a blog and White Paper posted on this website.

I have always arbitrarily defined ultra-early planting as anytime before about Apr. 5. However, in 2017,air temperatures in March have been considerably above normal (both max. and min. temperatures from Mar. 1-28 at Stoneville were nearly 5 deg. above normal), and this has caused some producers to consider planting soybeans in this ultra-early period. So this raises the question “what are the advantages/disadvantages from ultra-early planting such as in late March–very early April?”.

Regrettably, there is a paucity of data that can be used to answer this question. However, Dr. Trey Koger of Silent Shade Planting Company provided a slide he prepared from 2 years of data he collected from plantings that were made starting in January on a nonirrigated clay site using MG 4.7 varieties. Click here for that data.

The graphed data show there is no yield advantage to planting before mid-April. Be reminded that, even though these data show that good yield can be achieved from plantings made prior to that period, yield potential will depend on there not being a frost or freeze that will negatively affect plantings made prior to mid-April.

Plants in plantings made during the above defined ultra-early period will begin flowering very soon after emergence, and will likely be shorter than desired. That, plus the fact that pods on these plants likely will be close to the ground, will reduce harvest efficiency.

The shorter plants in ultra-early plantings dictate that they be grown in narrow rows, or rows that are 20 in. or less in width. Otherwise, these short plant will not form a canopy and this will result in problems such as season-long weed infestations that will be difficult if not impossible to manage.

I know of only one situation where planting soybeans in the above ultra-early window may be of benefit. If the planting site is a very sandy soil that will depend on frequent rainfall (say every 5-7 days) to provide plant available water as needed by soybean plants during the growing season, then planting in the ultra-early window may be the best option for avoiding the drought that will be the bane of yield potential of soybeans growing on these sites. Again, these sites are totally dependent on frequent rainfall for plant available water, and this is most likely to occur well before the beginning of summer. So planting early-maturing soybean varieties ultra-early may be the best option for these sites.

As with all things agronomic, there will be exceptions to all of the above. But since most agronomic recommendations are based on the generally best set of circumstances, the above should be considered before making the decision to plant soybeans before the perceived optimum planting window dates in the Midsouth.

Composed by Larry G. Heatherly, Mar. 2017, larryheatherly@bellsouth.net