Sulfur is very important as an additive for fertilizer. While it has other industrial uses, farmers depend on it to condition the soil, usually in concert with phosphate fertilizer. I know a bit about this, both as an ex-farmer, and as a mining company employee. Our firm, then known as Duval, a division of Pennzoil, had a very large underground molten sulfur mine in Culberson County, TX USA. It was one of the gems of our portfolio. The mine operated a bit like an oil well. The sulfur was underground in liquid form, under great pressure. We drilled wells into the formation, and injected steam to keep the sulfur molten as it came to the surface. It was piped into heated tanks, and then loaded onto special rail cars. We had a unit train that rolled twice a week from the mine to Galveston, and then returned for the next run. At Galveston, the sulfur was loaded onto our Duval ship, also steam-heating the sulfur to keep it liquid, and sailed to Tampa, where the sulfur was unloaded and a fertilizer miner/manufacturer there blended it into the finished product for farmers.
Many of the railcars we used were ours. We had a rail car shop on our site, competent to both repair and build rail cars with steam jackets that kept the sulfur molten as it rolled across Texas to Galveston. That was a story; when the mine started, the cars were leased. At that time (late 70s) the US had some tax rules that favored investment. If you bought an asset like a rail car for say $100,000, you could deduct the entire amount from your taxes in that very year! This little tax shelter attracted investors; doctors, lawyers, businessmen, people who had a few spare hundred thousands around they could get a total write-off for. It was good for the investors up front; but the car user, such as Duval, needed them all the time in the unit train.
Now you may not know, but if a rail inspector thought something was wrong with a car, such as bad brakes or hubs, they had the authority to pull it off the train and send it to a rail repair yard immediately. The repair work would be done in the shop’s good old time, and then the car went back into ‘service’. But that did not have to be the Duval train. The car could go anywhere.
Duval was a substantial firm, but not big business for the railroad. So we had little leverage to get the cars back. Often our precious heated sulfur cars would wind up in Mexico or some other out-of-the-way place, especially the ones owned by the doctors and lawyers, who had even less leverage than we did. So we had a licensed repair facility, and checked out the cars after each round trip, to reduce the chances of having a car pulled off. When the tax law was repealed, steam-jacketed cars were in short supply. So Duval made our repair facility into a construction facility as well, and gradually we built enough cars to fill the unit train, which I think was 150 cars long. That way we were the owners, and could make even more sure to get them back each trip.
On a side note, guess what happens if the steam jacket isn’t kept hot— the sulfur solidifies. You may remember from high school chemistry that sulfur has several solid phases at normal temperatures, and the one that was in a cooled car was a brown glasslike solid, not the pleasant yellow sulfur crystals you might be familiar with. Then you have to steam the cars extra hard for a couple of days to get the sulfur to change phase to the liquid form needed for transport and removal. The same is true in spades on the ship, and in the inventory tanks at each end. Don’t let the sulfur cool down!!
I understand that the Culberson County liquid sulfur mines closed down in the 90s; all the operational expense was too much; sulfur as a by-product of oil refining was cheaper and closer to Tampa; that’s what is used today. It’s still transported molten, though. according to the story below, “Third-quarter molten sulfur contracts delivered to Tampa, Florida, settled at a record $705 per long ton, up from $655 in the second quarter, while U.S. Gulf spot export prices reached $1,100 to $1,150 per metric ton in July as buyers competed for supplies that would normally have come from the Middle East”.
Middle East, got that? Hormuz has lots of oil refineries, and hence lots of sulfur to export. So we have shortages of sulfur to combine with phosphate for fertilizer. Many domestic fertilizer plants are reducing production because they can’t get enough sulfur. One ton of DAP fertilizer requires roughly 1.5 to 2 tons of phosphate rock, 0.4 ton of sulfur and 0.2 ton of ammonia. Some plants are running close to 40% of capacity.
The article indicates also that sulfur is becoming more important for farmers as a crop nutrient. It’s partly because of our efforts at cleaning up the air. Farms historically received substantial sulfur through atmospheric deposition, as sulfur dioxide from coal-fired power plants and industrial facilities ultimately settled onto farmland as sulfate. Air-quality improvements have sharply reduced that source: Iowa State University agronomists report that atmospheric sulfur deposition in Iowa has fallen to almost zero and estimate that plant-available sulfur in soils has declined 34% to 86% over the past two decades, making deficiency in corn and alfalfa increasingly common.
However, more sulfur isn’t always the answer. High nitrogen rates do not cause sulfur shortages in soil. It’s just that adequate nitrogen removes a yield constraint, and makes sulfur the next binding constraint. And actually, some farmers may be applying sulfur too frequently. Sulfur does not disappear as quickly from soil as some people think, and you might not need to apply it every year; maybe four years on, then two years off. Testing is the trick.
The moral of the article is that we’d better start paying attention to sulfur for agriculture and its complex supply chains, not just bundle it with the cost of fertilizer.
Posted Friday, August 28, 2026 8:00 am By Jessica Hunt
