The Strait of Hormuz and your butter
When the Strait of Hormuz effectively closed in March, it didn't just disrupt oil. A third of the world's fertiliser trade moved through that channel. NZ farming is feeling it.
There's a narrow channel of water between Iran and Oman, roughly 33 kilometres wide at its tightest point. In early March, commercial shipping through it effectively stopped. That single chokepoint handles around 20% of globally traded oil, a similar share of LNG — and, less noticed, about a third of the world's fertiliser trade.
For New Zealand farmers, that last figure matters more than most people realise.
Urea prices in the Middle East have risen to around US$650 a tonne — roughly double where they were a year ago — with up to 45% of global urea supply at risk from the disruption. Urea is the most common form of nitrogen fertiliser used in New Zealand agriculture. The dairy sector alone accounts for around 63% of all nitrogen fertiliser use nationally.
Here's the thing about urea: it doesn't come from soil. It's manufactured. New Zealand does have one ammonia-urea plant, built at Kapuni in South Taranaki in 1982, using natural gas from the Māui gas field. It produces roughly a third of what the country uses. The rest is imported. Over a fifth of NZ's global fertiliser supply comes from Saudi Arabia — which exports via the Strait of Hormuz. New Zealand holds no meaningful fertiliser reserves.
Ravensdown's chief operating officer Mike Whitty has been measured about the near term: NZ is in a reasonable position with stock either in the country or on the water for autumn, and there's a three-to-four month lag between ordering and delivery. Not an immediate shortage, then. But a structural exposure, quietly sitting there, now visible.
How the strait actually closed
Worth pausing on, because the common framing — that Iran closed the strait — isn't quite right, and the accurate version is more revealing.
Iran didn't physically blockade the waterway. It attacked enough vessels that the commercial risk calculus collapsed on its own. Transits fell 81% in a week. War risk insurance premiums reached levels that made most voyages economically irrational — reportedly $10–14 million for a single passage by a large tanker. Crew members gained formal rights to refuse under maritime labour contracts. Lloyd's Market Association was direct: "The reason ships are not moving is not through a lack of insurance; it is a question of the risk to crew and vessel safety."
The strait remained physically and legally open. It closed commercially. Iran didn't need a minefield — it needed to make the risk calculus unworkable, and the market did the rest.
That's the more unsettling version for anyone thinking about food supply. NZ's fertiliser doesn't just depend on geopolitics. It runs through a financial architecture — war risk underwriters, P&I clubs, freight markets — that most people in the food chain have never heard of, and that can seize up not through force but through the withdrawal of actuarial confidence.
Where does organic fit in this picture?
Certified organic farming in New Zealand prohibits synthetic nitrogen fertilisers. No urea. Nitrogen comes instead from biological fixation — clover and legumes pulling it from the atmosphere into the soil — plus compost, animal manure, and careful management of organic matter.
This isn't a new technology. Prior to the 1990s, New Zealand's pastoral systems were almost solely reliant on clover to fix nitrogen. Synthetic nitrogen wasn't a foundation of the system; it became one, gradually, as the dairy herd intensified. Organic farms never made that transition.
Recent European research found regenerative farms used 61% less synthetic nitrogen than conventional counterparts, with yields only around 2% lower. The NZ organic sector operates on similar principles — and while that research comes from the other side of the world, the underlying logic holds here too: farms that build nitrogen from within carry a different exposure profile when global supply chains seize up.
Different, not immune. Organic farms still run on diesel. Some use imported biological inputs with their own supply chain dependencies. The resilience is partial and specific — but on this particular vulnerability, it's real.
What this crisis is actually revealing
New Zealand's exposure to the Hormuz disruption is, as one analyst put it, "upstream, invisible, and offshore." The fuel price is visible at the pump. The fertiliser risk is less so. Downstream of fertiliser is pasture growth, dairy output, vegetable yields.
The call for a national food security plan — renewed loudly in recent weeks — rests on exactly this logic: not finding ourselves dependent on a few suppliers or supply routes, because when something goes wrong, you run out of options fast.
New Zealand has built an agricultural system that produces impressively for the world. In doing so, it quietly built supply-side dependencies most consumers never see. The urea price spike won't empty supermarket shelves tomorrow. But it makes visible something that was always there.
Farms that build their nitrogen from within are, structurally, different kinds of farms. That's not a moral argument. It's just what this moment makes clear.
Jamie Gray
