With April now here, the talk of planting will be a daily talking point for farmers across Iowa. With new genetics, more seed treatments, better tile drainage, farmers are pushing the planting date earlier for corn and soybean in Iowa. For 2023 the early crop insurance date is April 10th for both corn and soybean in southern Iowa for the northern 2/3rds of Iowa the soybean date is April 15th. Based on the drier conditions here in SW Iowa, I expect a NASCAR like start to the planting season. While it is true soybean germination has been reported to temperatures as low as 36 to 39 degrees, we need to consider the time to emergence.
No one can predict the future but try to set up for success. So, we ask our selves the odds of cool temperatures in Iowa soils? Well, funny you ask. Below is a chart that can help you understand your risk profile. What this chart shows us is for example After April 10th in Lewis, Iowa we have an 82% probability of an average daily soil temperature of being below 50 degrees based on soil temperature history at this site.
|
Spring 4" soil temperature probabilities for Lewis, Iowa. |
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|
4" Average soil temperature |
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|
Date: |
50 |
45 |
40 |
35 |
32 |
28 |
23 |
|
|
1-Mar |
88 |
88 |
88 |
82 |
50 |
29 |
17 |
|
|
6-Mar |
88 |
88 |
88 |
82 |
38 |
21 |
17 |
|
|
11-Mar |
88 |
88 |
88 |
76 |
31 |
7 |
17 |
|
|
16-Mar |
88 |
88 |
82 |
53 |
12 |
7 |
17 |
|
|
21-Mar |
88 |
88 |
76 |
41 |
12 |
7 |
17 |
|
|
26-Mar |
88 |
88 |
53 |
24 |
12 |
7 |
17 |
|
|
31-Mar |
88 |
88 |
47 |
18 |
6 |
7 |
17 |
|
|
5-Apr |
88 |
59 |
35 |
12 |
6 |
7 |
17 |
|
|
10-Apr |
82 |
41 |
24 |
6 |
6 |
7 |
17 |
|
|
15-Apr |
71 |
24 |
6 |
6 |
6 |
7 |
17 |
|
|
20-Apr |
47 |
0 |
0 |
0 |
0 |
0 |
0 |
|
|
25-Apr |
41 |
0 |
0 |
0 |
0 |
0 |
0 |
|
|
30-Apr |
18 |
0 |
0 |
0 |
0 |
0 |
0 |
|
|
5-May |
6 |
0 |
0 |
0 |
0 |
0 |
0 |
|
|
10-May |
6 |
0 |
0 |
0 |
0 |
0 |
0 |
|
|
15-May |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
|
|
20-May |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
|
When planting soybeans consider the soil conditions and the future forecast. Research has indicated on average a need for approximately 160 to 200 Growing Degree Days for 75 to 90 percent emergence (Casteel, 2021). When considering early planting take a few key take aways.
- Plant proven cool temp varieties with good cold tolerance.
- Consider fungicide treated varieties and hybrids
- Planting depth corn 2” soybeans 1.25 to 1.5 “
- Soil types and drainage
- Future forecast for temperature, sunshine, and precipitation. TRY to avoid conditions that cause imbibitional chilling.
To make your own specific 4” soil temperature map from a site closer to your farm use this link to the Iowa Environmental Mesonet.
We have better genetics today than decades ago, so cold temperatures may or may not play a role in final yield that it did decades ago, we still need to be aware of the below ground factors affecting crop growth and development.
Aaron Saeugling Field Agronomist in SW Iowa
Aaron Saeugling is a field agronomist in southwest Iowa for Iowa State University Extension and Outreach.
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