Diesel and the Harvest

Diesel passed six dollars a gallon in September. Before the war with Iran began in February, it was under four.

That matters for the fall harvest. One Iowa farmer put the cost of running his combine at a thousand dollars a day — and harvest can run thirty days.

Fertilizer is the other half of it. About a third of the world's seaborne fertilizer moves through the Strait of Hormuz, which has been largely closed since the war started. Prices spiked hard in the spring. They've eased some — but anhydrous ammonia, the nitrogen farmers put down this fall for next year's crop, is still over nine hundred dollars a ton.

Here's what's genuinely uncertain. Higher input costs also tighten supply, which can push crop prices up. In 2022, that offset was enough to protect farm income. Whether it works this time depends on how long the strait stays closed.

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The war and the chokepoint. The conflict began February 28, 2026, with U.S. and Israeli airstrikes on Iran, and triggered the closure of the Strait of Hormuz — the passage through which roughly 20 percent of the world's traded oil and significant volumes of liquefied natural gas move. Brent crude rose from about $70 per barrel to over $110 within days. (Purdue Center for Commercial Agriculture)

Diesel. The national average was $3.72 to $3.81 per gallon the week before the war began, depending on the source — Bureau of Transportation Statistics reports $3.72, AAA $3.76, and WPR cited $3.81. The script says "under four dollars" rather than picking among them. Prices reached $5.35 by late April, hit $5.85 on September 4 — reported as a record — and were around $6.05 by September 11-12. That is roughly a 60 percent increase in six months.

A caution on "record." Outlets are reporting the September figures as all-time highs, and that is standard practice for fuel prices, but the comparison is nominal. Diesel peaked near $5.81 in June 2022, which is roughly $6.40 in current dollars — so in inflation-adjusted terms this may not yet be a record. An earlier draft of this script said "the highest price on record" and the phrase was cut for this reason. (Fortune/AP; Daily Caller citing BTS)

Harvest fuel cost — the Iowa figure. Navigator Research conducted two in-person focus groups with Iowa farmers on September 10, 2026, published September 18. One participant said it would cost him $1,000 per day to run his combine during fall harvest. Another described the squeeze plainly: "We're just kind of still doing the same thing we're doing, but the fuel prices are just killing us…because it's double what we are accustomed to paying."

Two caveats on this source. Navigator states explicitly that qualitative focus-group results are not statistically projectable — this is one farmer's figure for his own operation, not an average. And the $1,000 figure is Navigator's summary of what the participant said rather than a direct quotation. The script attributes it as one farmer's account for this reason. Nearly all participants self-described as independent, Republican-leaning, or strong Republican.

For comparison, the AP interviewed Jason Kurtz, a corn and soybean farmer near Forest City, Missouri, whose combine uses 200 gallons a day and who expected to run it about 30 days, plus additional diesel for a tractor and trucks. A Florida farmer described "an average day of harvest" at 400 to 500 gallons, likely covering a whole operation rather than a single machine. An earlier version of this script used "hundreds of gallons a day"; the Iowa dollar figure replaced it because a cost is more legible to a listener than a volume, and because the source is regional. (Navigator Research; Fortune/AP; WEAR-TV)

Fertilizer — and why the script avoids specific urea figures. Roughly a third of global seaborne fertilizer transits the Strait of Hormuz. Gulf Cooperation Council members supply about a quarter of global urea exports, and natural gas accounts for 70 to 80 percent of the variable cost of ammonia production, so a gas price shock passes straight through to nitrogen.

The trajectory: urea was $455 per ton on February 27, the day before the war. It reached nearly $700 by late April and peaked above $800 in the spring. It has since fallen. DTN reported retail urea at $655 per ton in the fourth week of August, down 5 percent month over month, and urea futures dropped further in September — explicitly attributed to "signs of progress in negotiations aimed at restoring shipping through the Strait of Hormuz," along with China relaxing export restrictions and weakening seasonal demand.

Anhydrous ammonia has moved differently and is the more relevant number for a fall audience: $923 per ton in late August and still rising, against $862 in February. Michigan Farm Bureau's analysis found farm-level urea prices jumped 56 percent after the strike while anhydrous rose 33 percent — the increases were not uniform. Because these prices move weekly and in different directions, the script describes the pattern rather than citing figures that would date it. The anhydrous number is the exception, because anhydrous is applied in fall for the following year's crop, which is the decision a listener faces right now. (DTN, Sept. 2; Trading Economics; Michigan Farm News; WPR/Harvest Public Media)

The affordability squeeze. An American Farm Bureau Federation survey found roughly 70 percent of responding farmers nationwide could not afford all the fertilizer they needed. Note this is a survey of self-selected respondents rather than a representative sample. USDA projects U.S. farm spending on fertilizer, lime, and soil conditioners will rise 15.3 percent in 2026, about $5.3 billion. CoBank reported fuel and fertilizer prices up 20 to 40 percent since the war began, and warned that higher diesel costs alone could add thousands of dollars per farm. (WPR; Daily Caller citing USDA)

The offset argument — the script's closing paragraph. Purdue's Ken Foster and Bernhard Dalheimer published a balanced assessment in March 2026 making several points the script draws on directly: farmers are not passive, and adjustments to fertilizer application rates and crop mix will moderate yield losses while simultaneously tightening grain supplies and supporting output prices. Farmers who pre-purchased or contracted fertilizer before the conflict are largely protected for the 2026 season, so exposure is heavily determined by purchasing timing. And historical precedent, notably 2022, shows that sustained energy-driven cost shocks often produce enough commodity price response to preserve and sometimes improve net farm income.

Their bottom line is the script's: "Duration is everything: a short conflict resolved in weeks is likely a manageable cost squeeze; a prolonged Strait closure would eventually push grain prices high enough to partially offset margins." (Purdue)

Why the offset may not hold this time. Two complications worth noting. Farmers facing high input costs may cut fertilizer application, which reduces yield — so the same farmer can face both higher costs and lower production. And the tariff environment has weakened export demand for soybeans in particular, which limits the price response that would otherwise offset input costs. Several farmers interviewed this fall described a "half crop" from drought on top of the cost increases.

Related Civic Minute segments: the energy series, particularly on fuel prices and supply disruption.