Written by Ryan McGuine //
The incredible crop yields made possible by modern, intensive agriculture have literally made it possible to feed the world. Fossil fuels, which are used to power mechanized cultivation and as feedstocks for fertilizers and pesticides, are central to intensive agriculture. Indeed, comparisons of historical energy returns to farming (the ratio of food energy harvested versus the energy needed to produce those harvests) clearly indicate two distinct eras: one dominated by food energy inputs for human and animal labor, and another dominated by fossil fuel inputs. Chief among the fossil fuel-derived agrochemicals is nitrogen fertilizer, in the form of ammonia.
In 1843, Justus von Liebig worked out that of the macronutrients nitrogen, phosphorus, and potassium, the one in shortest supply will determine the crop yield. Even though nitrogen is abundant in the air, it has proved the most challenging of the three to provide in a form that could be applied to fields. However, in 1909 Fritz Haber discovered a high pressure reaction between natural gas and air to synthesize ammonia, a compound rich in nitrogen, which was later commercialized by Carl Bosch at BASF. The Haber-Bosch process is now responsible for the majority of the world’s nitrogen fertilizer, and has transformed diets around the world — humans have doubled nitrogen flows into the environment in just 50 years, and today’s diets would contain nearly 40% fewer calories in its absence. Traditional diets based on a few staple cereals, legumes, and tubers have been replaced by a wide variety of fruits and vegetables, and increased meat, dairy, and fish. Due to land constraints, though, supplying that meat and dairy cannot be supplied by expanded grazing. and must be achieved by the intensifying feed crop cultivation.
Growing more food on less land is central to the development process — it raises farmers’ incomes, while freeing up labor to do more creative or more productive activities. Increasing crop yields is also good for the environment because it helps prevent deforestation of less fertile, more biologically important areas. For example, tropical forests are incredible stores of carbon dioxide and biodiversity hotspots, but the cleared land is not very good for growing crops, so ever more forest must be cut down. Meanwhile, the soil in places like Iowa or Kansas is very fertile, and much of the biodiversity exists is underground, making them great locations for intensive agriculture. In addition, while many in low-income countries would benefit from higher meat consumption, eating marginally less meat in the developed West would help reduce land use in the coming decades. Staple crops like cereals, legumes, and tubers have lower environmental footprints per calorie than fruits and vegetables by many metrics, so replacing meat with staples is more sustainable than doing so with fruits and vegetables.
However, the environmental impact is not all good. Nitrogen fertilizer leads to both local water pollution, and global air pollution. Regarding the former, it makes its way from farm fields and into waterways, where it causes problems like large algae blooms which are unpleasant to humans and toxic to aquatic wildlife, and contamination in drinking water that people depend on. Regarding the latter, it stimulates microbes in the soil to convert nitrogen to nitrous oxide, a potent greenhouse gas, at a faster rate than occurs naturally. As such, nitrogen fertilizer is an example of a negative externality, in that it creates a profit for farmers, but also creates a range of costs which get distributed across society. This means that ammonia, and the price that consumers pay for food, is cheaper than it would be if the cost of ecological damage was paid by farmers.
Fertilizer runoff follows the environmental Kuznets curve, so even though more fertilizer than ever gets applied today, less than ever gets taken up by crops. The nitrogen use efficiency (NUE) of grain crops in small-scale test plots can reach 85-90%, but NUE in commercial fields is never that high — average NUE in the USA is 68%, 30% in India, 25% in China, and 72% in Africa. In the USA, application does not change very much between years and efficiency has been slowly increasing for decades, while application has doubled in Asia over just 20 years, and remains persistently low across Africa. Similar to other global environmental challenges, reaching sustainability targets probably requires different responses by different regions. In this case, success might look like sustaining marginal annual NUE growth in technologically-advanced places where fertilizer is already widely used like Europe and the USA, rapidly raising Asia’s NUE, and preventing Africa’s from dipping too low as it expands application in pursuit of better yields.
There are a variety of solutions based on farming practices that can reduce nitrogen runoff. For example, no-till farming practices paired with cover crops (things grown during the winter when fields are usually left empty) increase the nutrient content in soils, reduce pests and weeds, and keep fertilizer from washing off fields. Further, anywhere from 5-15% of cropland is not very good — including hillsides with eroded soil, low-lying land which accumulates rainwater, etc — and planting strips of prairie grasses, whose deep roots are effective nitrate sinks, on the least productive land could reduce nitrates in water leaving fields by up to half. In poor countries, NUE can be improved by applying nitrogen only when and where it will actually reach plant roots, which can be done with low-tech methods like fertilizer briquettes that can be planted close to roots, as well as with high-tech “precision agriculture” practices. These include using algorithms to analyze plant health and soil conditions to customize the amount and timing of fertilizer applications, and sharing that information with farmers via mobile phones.
There are also policy solutions that can help. First, and most importantly, governments should pay farmers that utilize the solutions listed above because they are crucial to preventing long-term environmental damage, but do little for farmers’ immediate bottom lines. Second, reducing food waste would help reduce fertilizer application, since roughly one-quarter of all food produced globally is thrown out. Most food waste occurs “close to the fork” in high-income countries, but “close to the farm” in low-income countries, so it can be reduced by donating unmarketable crops and changing food date product dating practices in the former, and enhancing access to markets, increasing the amount and quality of post-harvest storage in the latter. Third, very large sellers of food can leverage their buying power to push suppliers to source crops from farms that minimize environmental impact per calorie. One model of this approach is Walmart’s Project Gigaton, which seeks to avoid 1bn metric tons of greenhouse gases from its supply chain by 2030, and includes agriculture as a focus sector.
Finally, there are major institutional factors that could be improved. For example, many farmers do not own their own land — up to half of farmland in the American midwest is not owned by those who farm it, and there have been multiple waves of recent farmland acquisitions in low-income countries by foreign investors — which reduces incentives for them to invest in the very long-term future of their land. Additionally, agricultural subsidies constitute gigantic, tangled webs which make price movements in agricultural commodity markets challenging to interpret without an intricate knowledge of the various policies. These distort farmer incentives even more, and in most countries disproportionately reward large-scale, monocrop farms growing animal feed.
Intensive agriculture enabled by nitrogen fertilizer is integral to today’s high level of well-being — no method of traditional agriculture can consistently produce enough food to eliminate widespread malnutrition on its own — but doing less of it on the margin in order to maintain the land’s ability to support it is prudent. Being the unfortunate side effect of gigantic, commodity industries that underpin modern life, the sheer scale makes nutrient pollution feel intractable. However, it also means that small changes by a few actors have the potential to make an outsized difference. Thus, the most effective path to minimizing nutrient pollution probably requires some combination of more low-intensity agriculture, continually improving the intensive agriculture that is done, and finding new and better ways to feed people like vertical farming and meat alternatives.