Nitrogen is the fragile link in the food chain, and the substitutes do not arrive in one season

An explainer published by phys.org restates a dependency that most food-price commentary skips: research suggests roughly half the world's population is fed thanks to synthetic nitrogen fertilizers ^[1], and making those fertilizers is a gas business before it is a farming one ^[4]. That is why a disturbance in energy markets eventually shows up as a higher price for bread, breakfast cereal and dairy ^[9].

The chemistry leaves little room to manoeuvre. Nitrogen is almost 80% of the air, but plants cannot use it until it has been converted into forms such as ammonium or nitrate ^[2]. The Haber-Bosch process does that industrially, combining atmospheric nitrogen with hydrogen at extremely high temperatures to make ammonia, which is then turned into urea and ammonium nitrate ^[3]. Natural gas, mainly methane, supplies both the energy to run the factories and the hydrogen itself ^[4]. So the price of a tonne of urea follows the gas market closely, and rises quickly when energy does ^[5]. According to the article, recent disruptions to global energy supplies, including Russia's invasion of Ukraine and the prolonged U.S.-Iran war, have caused nitrogen fertilizer prices to surge ^[6].

The demand side has almost no give. Farmers cannot simply stop applying nitrogen: too little means lower yields, poorer grain quality and reduced income ^[8]. Australia's exposure is structural rather than seasonal, since the country imports about 3.5 to 4 million tonnes of fertilizer a year, which leaves growers there vulnerable to fluctuations in international energy markets ^[7].

Building more domestic ammonia capacity is the obvious industrial answer, and it carries its own bill. Haber-Bosch is one of the world's largest industrial sources of greenhouse gases, with ammonia production accounting for roughly 2% of global carbon dioxide emissions and generating between 430 and 500 million tonnes of carbon dioxide each year ^[10]. Taken at face value, that share and that tonnage imply a global total of about 21.5 to 25 billion tonnes of carbon dioxide ^[11]. New plants would be added to a process that is already a large emitter ^[12], so import substitution does not come free.

That is the context for the biological options, and it is worth being precise about what they are. Organic and biological fertilizers are made from compost, animal manure and other recycled organic matter, usually converted through composting or anaerobic digestion, in which microorganisms break down the material into nutrient-rich products ^[13]. Some are inoculated with beneficial microbes that help plants access nutrients, either by releasing them as the material decomposes or by colonizing roots and the surrounding soil ^[14]. Existing research has yielded promising results, with certain biofertilizers improving crop yields and nutrient absorption ^[15].

The limitations are the operational story. Biofertilizers typically contain far lower concentrations of nitrogen than conventional products, so a farmer must apply more of them to deliver the same plant-available nitrogen ^[16]. That is a tonnage, handling and spreading problem, not just an agronomic one. They may also release nutrients only at certain temperatures, or in soils with enough moisture or enough beneficial microbes, which makes them less predictable than synthetic fertilizer, with soil type among the other variables ^[17]. These are management tools that need matching to a field, not drop-in replacements that can be ordered in a tight year.

Worth watching: whether biofertilizer products start being sold on plant-available nitrogen per tonne rather than on category claims ^[16], whether trial results specify the soil temperature and moisture conditions under which nutrients were actually released ^[17], and whether Australia's import volumes move at all as gas-linked prices move ^[7].