Harvest now or wait: what drying costs against what the field loses
Sigurd Lindquist, CCA, Chetek, Wisconsin
Every point corn dries on the stalk is a point you do not pay to dry. Every day it stands, some of it can go on the ground. Put in your corn, your fuel and your bid, and the page shows the drying bill now and after 7, 10 or 14 days. How much the field loses is your call; the page tells you how much it can lose before waiting stops paying.
Drying cost
0.018 gallons is Iowa State's average for a high-temperature dryer; they give 0.010 to 0.025 depending on the dryer and the weather.
Your bid and your weather
Type your bid, or let the page fill one in.
Field loss, your number
Leave field loss blank and the page shows how much loss waiting can stand. Stalk quality, lodging, ear drop and the weather decide the real number; you know your field.
Enter your moisture, yield and drying cost.
Day by day
| Day | GDD | Moisture | Drying $/ac | Saved | Break-even loss, bu/ac |
|---|---|---|---|---|---|
| Fills in from your numbers. | |||||
GDD is the forecast heat that day (86/50). Moisture is the estimate. Saved is drying saved against harvesting today; break-even loss is the field loss, in bushels an acre by that day, that would eat it.
Moisture by the monthly drydown rates below. The forecast heat column fills in once you enter a ZIP.
Show the math
How fast corn dries in the field
NDSU extension engineer Ken Hellevang put the usual field drying by month in a table, and Iowa State used the same rates in 2022. Standing corn dries toward the air's equilibrium moisture and slows as it gets close, so the page stops at that month's number.
| Month | Points a week | Points a day | Dries toward, % |
|---|---|---|---|
| September | 4.5 | 0.64 | 15 |
| October | 2.5 | 0.36 | 16 |
| November | 1.0 | 0.14 | 19 |
| December | 0.5 | 0.07 | 20 |
NDSU also says standing corn dries about 0.3 to 0.4 points a day in October and 0.15 to 0.2 in November in normal weather, and that field drying is normally cheaper than the dryer until mid to late October, the dryer after that.
Some extension guides predict drydown from growing degree days instead of the calendar. The page reads your 14-day temperature forecast and shows the heat each day, but does not turn it into moisture until we have read those rules in the original publication. Until then the estimate is the calendar rate, or your own rate if you enter one.
What a point of drying costs
Iowa State's rule of thumb: gallons of LP = 0.018 x bushels dried x points removed. Purdue's fact sheet GQ-3 lists the heat a column dryer needs per bushel. An LP gallon holds 92,000 BTU, so fuel a bushel is the BTU divided by 92,000, times the price.
| From, % | BTU a bushel to 15% | LP gal a bushel | Gal a bushel a point |
|---|---|---|---|
| 22% | 12,589 | 0.137 | 0.0195 |
| 24% | 15,447 | 0.168 | 0.0187 |
| 26% | 18,118 | 0.197 | 0.0179 |
| 28% | 20,624 | 0.224 | 0.0172 |
| 30% | 22,978 | 0.250 | 0.0167 |
GQ-3 Table 1, column dryer at 100 cfm a bushel and 180°F air. Purdue's example: 28% to 15% with LP at 60 cents is 20,624 x 0.60 / 92,000 = 13.5 cents a bushel. The per-point column lands close to Iowa State's 0.018. Electricity for fans and augers is extra; GQ-3 figured 0.7 cents a bushel. Iowa State adds that a high-temperature dryer costs about 14% more to run for every 20 degrees colder the outside air, so a point dried in November costs more than one dried in October.
Questions
How fast does corn dry down in the field?
About 4.5 points a week in September, 2.5 in October, 1 in November and 0.5 in December. That is NDSU's table (Hellevang, 2009), and Iowa State used the same rates in 2022. NDSU also puts October at 0.3 to 0.4 points a day and November at 0.15 to 0.2. Their example: 35% corn on October 11 dries to about 27% by November 1 and about 22% by December 1. The weekly rates give 27.7% and 23.5%.
How much LP does it take to dry a point of corn?
Iowa State's average is 0.018 gallons a bushel a point in a high-temperature dryer, anywhere from 0.010 to 0.025 depending on the dryer and the weather. Taking 5 points out of 1,000 bushels is about 90 gallons. Purdue's GQ-3 table works out to 0.017 to 0.020 gallons a bushel a point drying to 15%.
When does waiting on field drydown stop paying?
When the corn stops drying or the field starts losing more than the drying saves. Corn dries toward the air's equilibrium moisture, which NDSU puts near 16% in October, 19% in November and 20% in December, and it dries slower each week. NDSU says field drying is normally cheaper than the dryer until mid to late October and the dryer is cheaper after that.
What field loss should I put in?
Yours. Stalk strength, lodging, ear drop, deer and the weather decide it, and they differ field to field. Leave it blank and the page shows the loss that would eat the drying savings. Purdue's GQ-3 example: drying 28% corn to 15% instead of 22% corn cost $7.02 an acre more in fuel and electricity at 130 bushels, so a field loss of 3.5 bushels an acre at $2 corn would pay for drying the wetter corn.
Does the weather forecast change the estimate?
Not yet. The page shows the forecast heat for each of the next 14 days, but the moisture estimate uses the published monthly rates or your own rate. Some guides predict drydown from growing degree days; the page will use that once we have read the rule in the original publication.
Where does the bid come from?
Type your own, or enter your ZIP and the page uses the nearest elevator's posted corn bid from the same boards as the cash bids page. With no ZIP, pick a state and the page uses the latest corn futures settle less that state's median basis, labeled as such.
Sources
- Hellevang, NDSU: Post-harvest tips for later maturing corn (2009). The field drying and equilibrium moisture table by month; points a day in October and November; the 35% corn example.
- TeBockhorst, Dougherty and Mensing, Iowa State ICM: Options for fall grain drying and marketing (Oct 20, 2022). Weekly drydown by month; 0.018 gallons of LP a bushel a point (0.010 to 0.025); 14% more fuel per 20 degrees colder.
- Uhrig and Maier, Purdue: Costs of drying high-moisture corn, Grain Quality Fact Sheet 3 (1992). BTU a bushel by moisture, 92,000 BTU a gallon of LP, and the break-even field loss.
Bids: the nearest posted bid comes from the same elevator boards as cash bids near me. The state default is the futures settle less the state's median basis from the basis page. Forecast temperatures: Open-Meteo, the same service the GDU calculator uses. Every number here is an estimate; your moisture tester and your fuel bill are the real ones.