Below is an article I sent out last April that is timely again with a few thoughts for this year added here.
- Since we have soybeans that were planted around the 10th of April and are already emerged, let’s talk about what the ramifications are for these soybeans in the freezing temps that we have experienced over the weekend.
- Soybeans need to be in the range of 28-30 degrees for several hours for tissue to be killed due to an anti-freeze-like substance produced by the soybean plant. The quick dips to 30 or 31 degrees that climb right back up, should not significantly harm newly emerged soybeans. Scouting to confirm this 3-5 days after the cold temps is the only way to know for sure.
- As we look at when our next planting should be, there are always at least three factors to consider: moisture, temperature and the calendar.
- Moisture: We absolutely don’t want to plant if moisture levels are not right. Too wet of soil will result in side-wall compaction, wheel traffic compaction, poor closing wheel results and increased exposure to soil borne fungal diseases like Pythium, Rhizoctonia and fusarium.
- Temperature: We can plant into too cold conditions but need to be aware of the consequences. I have said for three years now that on a personal note, my favorite thing about early planted soybeans is it keeps me out of the corn planter when I shouldn’t be in it. The sins of early planted soybeans can be overcome during the rest of the growing season. The sins of early planted corn are rarely forgiven, plain and simple.
- Calendar: The calendar is an interesting factor because we all know what the best early planting window is in our area because of years and years of local research. However, it is important to remember that an average is made up of highs and lows, early and late, to arrive at an average. Just like I don’t know what hybrid or variety is going to be the best in 2023, neither do we know what the best planting date is going to be. In 2022, the best planting date was the first half of May, an easy 2 weeks behind when we would have preferred to plant. In 2019, we worked our tails off to squeeze in some planting at the end of April, only to see late May and early June planted corn out-yield the early planting. This was due to the major cold injury and soil borne fungal disease injury suffered by that early planted corn.
I know these decisions are not easy and everyone is going to do what they think is best for their operation. This article is meant to stimulate thought on what to do and not as the gospel. As always, I respect your ultimate decision and the job you face. Good luck and here’s to hoping for a warmer forecast! |
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Thoughts on Planting Temperatures
To err on the side of caution for planting both corn and soybeans, it has long been considered ideal to have soil temperatures of at least 50°F at seeding depth and maintain that temperature or warmer for 24-48 hours. In recent years, driven especially by the adoption of early planted soybeans, additional testing has painted a clearer picture of this critical period in our production season. Let’s look at some of these scenarios. |
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The above study was conducted in a lab at the University of Nebraska-Lincoln in 2020. Don’t get caught up with all of the different colored bars. This was a blind study of different seed treatments. The take home point is, when they started out with soil temperatures in the 60°F range (left side of chart) and maintained these temperatures for at least 8 hours, the higher the percentage of soybean emergence. Looking at the right side of the chart, we see a cautionary lesson. Starting out with temperatures at 36°F did not result in satisfactory emergence no matter how quickly soil temperatures warmed.
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This chart demonstrates how soil temps fluctuate once we get into April. Basically, at planting depth, the soil temperature will follow air temperature with not much lag. Once soil temperature warms up to our target of 50°F, we can predict what these temperatures are going to do for the critical period after we plant our seed by looking at air temperature forecasts.
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This chart shows a real-world scenario from Spring of 2021 where a neighbor planted soybeans on a Saturday before a big temperature drop that night. As you can see, if you started at around 10AM and finished by 2PM, that is the safe zone where the soil should have been warm enough when you started and you would have at least 8 hours for that seed to imbibe water before those temps got dangerously cold.
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My neighbor stopped at the proper time and had an excellent stand. I think this type of information is valuable now that we are planting soybeans earlier and will always run into cold snaps during this time frame. It puts some research behind when to safely start and maybe more importantly, when to stop before a cold snap moves in.
You may ask what about recent studies that show lower temperatures like low 40’s, may be safe? This may prove to be accurate over time. However, I would recommend you err on the safe and proven side of this issue than the ragged edge that may be fine but may also result in unrecoverable injury to your very valuable crop.
| I am very confident in saying that there is a much greater margin of error on early planted soybeans than corn. Soybeans can compensate in dozens of different ways if injured early due to their growth habit. With corn, if we make a mistake early, a big chunk of yield potential is just gone and won’t be made up later in the season. That is why it is more important with corn to make sure that soil temperature is at or above 50°F and is going to stay that way for at least 36 hours.
The imbibitional chilling injury that can really damage the corn seedling will happen in the first 24-36 hours. Cold injury can still occur after this period but is not as damaging as imbibitional chilling. Ideally, we would like the soil temps to be above 50°F and stay that way until after emergence but that is not always in our hands or even realistic, considering the commonality of the cool springs we have experienced in the past several years. |
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If you have any questions, don't hesitate to contact your District Sales Manager or myself. Contact information can be found here.
-Craig Allaman, CCA
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