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  • Writer's pictureRachel

Should I Replant? Lets Talk Soybean Growth And Development.

The Agronomy Advisor 5/17/18

Should I replant beans? 

Many fields planted April 30 and May 1st ahead of the rain have been experiencing issues with crusting. Its important to think through some steps before making the decision to replant. Consider the following:

1. What was the reason for the replant? In this case crusting. Its important to decide if the conditions causing the replant have sufficiently changed to afford replant. Is the reason for the low stand in spotty areas of the field or uniform lower stands across the whole field?

2. The next step is to assess stand. Conduct stand counts at 1/1000th of an acre at multiple locations across the field, being careful to check both sideslopes and hilltops alike. 

3. Calculate expected yield for these lower stands. What percentage of total yield are we losing with this decreased stand? 

4. Calculate economic return. Does the yield gained from replanting more than cover the cost of the replant? If we don't replant, what costs might be added from an additional herbicide pass, or pod loss at harvest?

These are some of the main guidelines when assessing replant. Call us to discuss options or for help assessing population in the fields in question. These can be tricky decisions, and we're here to help you make them. 

Soybean Growth and Development

As soybeans continue to emerge across the county, we thought we'd give a quick refresher on soybean growth and development. After a soybean seed takes up water, cell division starts within 36 to 48 hours. The radical root will be the first plant structure to form.

Next, the hypocotyl will elongate to pull the cotyledons through the soil surface. The cotyledons have enough energy to supply the plant for 7-10 days. The plant also begins to photosynthesize with the cotyledons. If an issue like crusting causes the plant to lose both its cotyledons, this can result in a 2-7% reduction in yield for the plant. 

The unifoliates will be the next to form on the plant. These are a set of opposite leaves that form after the cotyledons. After the unifoliates come the first sets of trifoliates. We term growth stages based on how many sets of trifoliates have opened up. When we have two sets of trifoliates uncurled, that is called V2. V2 is the growth stage when the plant begins to fix N2. 

Those are the beginning growth stages of a soybean plant. We will discuss more of what goes on with a soybean plant as we get closer to the reproductive stage during the growing season. 

Weekly Mean Air Temperature

Departure from normal mean temperatures. Data and image from Kansas Mesonet. 

Warmer than normal temperatures were recorded last week in the region, with most of Brown county around 10 degrees above normal temps. Recent warm temperatures have resulted in accelerated growth for crops. However, this also means acclerated growth for weeds as well. Be on the lookout for weeds that may be smaller in size but approaching physiological maturity. 

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