Del Voight – Senior Extension Agent – Penn State Extension
28, April 2011
We are experiencing probably the most difficult spring in years. As we move into May growers, that still have two weeks of manure spreading and alfalfa to harvest, might find themselves planting much later than the ideal planting dates for the area. Research suggests corn will begin decrease in yield after May 10 somewhere between 2-2.5 bu/day as the planting window narrows there will be some economic considerations that may be required to make rational decisions. These charts from the Agronomy Guide might come in handy.
Table 1.4-8. Estimated grain yields for various planting dates and population rates. Figures shown are most applicable to fields with less than 125 bushels per acre
| Planting date | Plants/A at harvest | ||||||
|---|---|---|---|---|---|---|---|
| 12,000 | 14,000 | 16,000 | 18,000 | 20,000 | 22,500 | 25,000 | |
| Optimum yield (percent) | |||||||
| April 20 | 72 | 78 | 83 | 87 | 90 | 93 | 95 |
| April 25 | 75 | 81 | 86 | 90 | 93 | 96 | 98 |
| May 1 | 77 | 83 | 88 | 92 | 95 | 98 | 100 |
| May 6 | 78 | 83 | 88 | 92 | 95 | 98 | 100 |
| May 11 | 77 | 83 | 88 | 92 | 95 | 98 | 99 |
| May 16 | 75 | 81 | 86 | 90 | 93 | 96 | 98 |
| May 21 | 73 | 78 | 83 | 87 | 91 | 94 | 95 |
| May 26 | 69 | 75 | 80 | 84 | 87 | 90 | 92 |
| May 31 | 64 | 70 | 75 | 79 | 82 | 85 | 87 |
| June 5 | 59 | 64 | 69 | 73 | 77 | 80 | 81 |
| June 10 | 52 | 58 | 63 | 67 | 70 | 73 | 75 |
Table 1.4-8B. Estimated grain yields for various planting dates and population rates
| Planting date | Plants/A at harvest | ||||||
|---|---|---|---|---|---|---|---|
| 10,000 | 15,000 | 20,000 | 25,000 | 30,000 | 35,500 | 40,000 | |
| Optimum yield (percent) | |||||||
| Source: University of Illinois | |||||||
| April 1 | 54 | 68 | 78 | 88 | 95 | 99 | 99 |
| April 10 | 57 | 70 | 81 | 91 | 97 | 100 | 100 |
| April 20 | 58 | 71 | 81 | 91 | 97 | 100 | 99 |
| April 30 | 58 | 70 | 80 | 89 | 95 | 97 | 96 |
| May 9 | 55 | 68 | 77 | 86 | 91 | 93 | 91 |
| May 19 | 50 | 63 | 72 | 80 | 85 | 86 | 84 |
| May 29 | 44 | 56 | 65 | 73 | 77 | 78 | 75 |
| June 8 | 35 | 47 | 56 | 63 | 67 | 67 | 64 |
This spread sheet will allow one to compare corn to soybean incomes. farmdocdaily: Planting Delays and Switching to Soybeans: A New FAST Spreadsheet
With Corn which is heat dependent growing degree days become important. This chart details the latest planting dates based on a hybrid requiring 2600 heat units to develop. As the season progresses short season hybrids may need to be reviewed and used as necessary.
Soybeans do not lose yield at such a dramatic rate as corn however there are issues with switching. First off if any residual herbicides have been used the carryover can be an issue. Particularly for atrazine based products. ALS materials are another concern, however, there are STS varieties of soybeans that could work in that scenario.
In summary, it is too early to determine the best course of action as of today. It appears that in our area mid may returns to corn mimic soybeans however by the first week of June returns favor soybeans. More updates as this spring unfolds will be available through Extension research.
