The halt in fertilizer shipments from the Arabian Gulf due to the war with Iran brought to mind the German chemist Justus von Liebig, one of the leading advocates of the mineral nutrition theory for plants in the 19th century. Liebig is widely known for promoting what is now called Liebigs Law of the Minimum.

This law states that the scarcest essential nutrient is the one that limits plant growth. In other words, once farmers run short of one critical nutrient, adding more of the other nutrients cannot compensate for the missing element.

Liebigs law now appears set to impose itself in a major and alarming way during the upcoming planting season, because the Arabian Gulf supplies 36% of the worlds urea one of the main nitrogen fertilizers along with 29% of anhydrous ammonia, another key nitrogen fertilizer, in addition to 26% of diammonium phosphate and 13% of monoammonium phosphate.

To revisit some high school biology basics, nitrogen, phosphorus, and potassium are the primary nutrients required by plants. These nutrients do not come from air or water and must instead be supplied through the soil. One exception is certain legumes such as soybeans, which are capable of fixing nitrogen from the atmosphere for internal use.

Adding these nutrients to the soil improves both crop quality and yields. But massive quantities of two of the three key nutrients are no longer flowing from the Arabian Gulf.

At the same time, around 20% of the worlds liquefied natural gas exports from the Gulf region have also been disrupted. In countries such as India, imported LNG is used as a feedstock for domestic nitrogen fertilizer production.

There may also be additional complications affecting fertilizer supplies that are not yet fully visible.

Rising prices pressure farmers worldwide

Higher fertilizer prices have already pushed wheat farmers in Argentina to consider reducing their use of urea fertilizer, meaning less nitrogen availability for crops.

The alternative would be shifting toward crops that require fewer fertilizers, which could ultimately reduce wheat output.

In Egypt, one farmer decided to abandon wheat cultivation a fertilizer-intensive crop in favor of other crops, while cutting his planted area to only half of its usual size because he could no longer afford fertilizers, seeds, and other agricultural chemicals, including herbicides and pesticides that are often derived from petroleum products.

A recent survey by the American Farm Bureau Federation also showed that 70% of US farmers cannot afford all of their fertilizer needs.

Liebigs law goes beyond fertilizers

As is becoming increasingly clear, Liebigs Law does not apply only to agricultural fertilizers.

Modern farming equipment depends almost entirely on diesel fuel. The sharp rise in diesel prices came after US farmers had already made planting decisions for the current season, meaning the immediate impact will likely appear in the form of weaker profits rather than lower production.

However, if diesel prices remain elevated, farmers may eventually reduce planted acreage or switch to lower-cost crops.

Diesel clearly needs to be viewed as an essential agricultural input, just like fertilizer itself.

The foundational materials of modern civilization

The analysis extends far beyond agriculture, as Liebigs Law can also be applied to the critical inputs underpinning modern society as a whole.

Energy expert Vaclav Smil argues that the modern world depends on four core materials: cement, steel, plastics, and ammonia.

Ammonia, of course, is a key input for nitrogen fertilizer production, which has already been discussed. The other three materials are so deeply embedded in modern life that their importance often goes unnoticed.

Smil highlights an especially important point at a time when oil and natural gas supplies from the Arabian Gulf are being disrupted: production of all four materials relies heavily on fossil fuels.

Beyond these industries, the world now appears close to discovering that losing large amounts of oil and natural gas could constrain the production of a vast range of goods fundamentally dependent on these resources and their derivatives exactly as Liebigs Law would predict.

A real test for the global economy

The risk of such constraints on the global economy was always visible to those willing to see it, but the dominant assumption had long been that such limits would never truly emerge, or that if they did, they would only be temporary.

That assumption is now facing a real test.

And if oil analyst Art Berman is correct in his assessment that the world may never again return to the pre-war levels of oil production seen before the conflict with Iran, then the belief in unlimited supply will have to give way to a new reality one defined by constrained production of many of the worlds most essential materials.