On March 12, 2026, a farmer in Sussex County, Delaware, opens the rotation plan for six fields and finds a crop name beside each one and nothing else. This is an example. All six fields passed last season’s check because the planned crop went in, yet nothing on paper says whether the rotation held back a pest or a disease. Lateness costs money too: in Illinois trials, soybeans planted June 20 yielded about 10 bushels an acre less than soybeans planted May 20, or $100 an acre at an example price of $10 a bushel. So before planting, write beside each field the problem the rotation targets, the date you measure it and the crop that goes in if planting slips past a set date.
A rotation is a planned order of different crops in the same field. Ticking off the planned crop answers whether the plan was followed. Whether it worked needs a second line beside each field: the problem the crop order is meant to hold back.
Can corn and soybeans taking turns still let a pest build up?
Yes, and which one depends on the field. Start with soybean cyst nematode, or SCN, a microscopic worm that feeds on soybean roots. A nonhost is a crop the worm cannot feed on. The management guide written by university specialists says that in a field planted to a nonhost, SCN numbers will not increase and should decrease, and its list of nonhosts includes corn and wheat.
Wheat gives less than it seems. The same guide says that soybeans double-cropped after wheat count as a full year of soybeans, because a significant increase in SCN is just as likely there. The worm can also cost yield without any visible sign: the guide says SCN can cause substantial yield loss without causing symptoms. Looking at the plants does not tell you whether the rotation held it back.
White mold runs on a longer clock. The fungus survives in the soil as sclerotia, resting structures that release the spores that infect the crop. The Crop Protection Network says that two to three years of a nonhost crop, such as corn or small grains, can reduce the number of sclerotia. Sclerotia buried 8 to 10 inches deep can stay viable for more than three years. One year of corn between two soybean crops falls short of that minimum in a field with white mold.
Which crop answers which problem is for the farmer and the agronomist to decide; what the agronomist decides sets out that split. Write the problem beside the field so the decision has something to answer.
When should you measure whether the rotation worked?
At a time of year you fix in the plan, and the same time every round. For SCN, the guide says the ideal time to sample the soil is as close to soybean harvest as possible, when numbers tend to be highest. Counts taken in different months are hard to compare.
How far a nonhost crop lowers SCN depends on where the field is. The guide says numbers may decrease by as much as 90 percent in the southern United States but only 10 to 40 percent in the north. It adds that several rotation sequences may be needed before an appreciable drop shows. One round of counts proves little in either direction.
So write the count and its date for each field, and compare the same field year by year. The field’s yield goes in the same row; each field’s yield year by year shows how to keep that record.
What do you do when the planting window closes?
Set the last planting date for each field ahead of time, and write the crop that replaces the planned one if that date passes. Without that line, someone decides at the tractor, field by field.
What late planting costs comes from planting date trials. Irwin, at the University of Illinois, reports soybean trials at six Illinois sites from 2010 to 2020, with the cumulative yield loss by date in bushels and in percent. Losses stay small until about May 10 and then climb quickly.
| Planting date | Bushels lost per acre | Share of yield lost |
|---|---|---|
| April 20 | 1 | 2% |
| April 30 | 2 | 4% |
| May 10 | 4 | 6% |
| May 20 | 7 | 10% |
| May 30 | 10 | 14% |
| June 10 | 13 | 19% |
| June 20 | 17 | 25% |
These are Illinois trials, so the Sussex County farm should ask its state extension service for trials near its fields. Irwin also warns that the response of yield to planting date is uncertain, especially for very late planting. Treat the table as a size of the risk, not a forecast.
The window rule has three parts: the last date to plant the planned crop in that field, the crop that replaces it, and who decides, the farmer or the agronomist. At planting, record each change as “followed the rule” or “decided on the spot”. At season’s end, that record separates a late spring from a plan that did not hold.
Does rotating pay?
It often does, and the clearest loss comes from dropping rotation altogether. Davis and colleagues ran a trial in Iowa from 2003 to 2011 that set a corn-soybean rotation against 3-year and 4-year rotations adding a small grain and a forage legume. With reduced agrichemical inputs, the longer rotations gave yields and profit similar to or greater than the two-year rotation’s.
A farmdoc budget from 2012 puts numbers on the other direction. At its long-run prices of $4.50 a bushel for corn and $10.50 for soybeans, returns were $364 an acre for corn-corn-soybeans, $362 for corn-soybeans and $299 for continuous corn. Its projected 2012 prices were higher, at $5.35 and $11.85. At those, leaving corn-corn-soybeans for continuous corn paid $16 an acre more in the first year, then $23 less in the second and $37 less in every year after.
The figures date from 2012 and your costs differ. The article itself says each farm should use its own projected costs. The pattern to check is the timing: dropping rotation pays at once and costs later.
What do I write first, and who checks it?
Write the sequence and the problem for the field with the longest history of trouble, and agree the measuring date with your agronomist before the next planting. The dated page is what the end of the season is checked against.
The sequence itself is set in the three-year production plan, and the same page-and-check habit works for any other line of farm management.