To understand why fertilizer works, we need to get some basic plant biology out of the way. Plants need large amounts of three nutrients: nitrogen, phosphorous, and potassium. Combine those with water and sunlight and plants will grow.
In a natural ecosystem, nutrients are naturally cycled. Plants grow, using these substances, then they die. Microbes decompose them and new plants use the same nutrients to grow again. You know, the whole circle of life thing.
Agriculture gives us civilization exactly because it disrupts this balance. Humans use plants to mine nutrients out of the soil and then eat them. We can even measure the amount of nutrients that a crop can mine for us. For example, a hectare of maize in the US needs about 22 kilograms pounds of nitrogen per tonne of yield. We call this the plant’s mineral uptake. Problem is, the corn on the cob you’re eating is full of the nutrients that the next generation of plants would have used. We’ve taken nutrients out of the cycle, so we’ve got to replace them or the soil will be depleted.
That’s the point of a fertilizer. Since the beginning of agriculture, people have tried to stuff as much nitrogen, phosphorous, and potassium into the soil as they could. But nitrogen, above all, is, as a Cornell paper put it, "the essential element." While phosphorous is needed to make carbohydrates, nitrogen is a necessary component of proteins, which have long been known to be " the most important and most essential part of our food".
Manure has some nitrogen in it, which is why it was used on fields. Some plants — legumes — evolved the ability to support colonies of bacteria that pull nitrogen from the air and convert it from its inert N 2 (dinitrogen) form into ammonia (NH 3).That’s why people have tended to rotate crops throughout time, trying to balance the differing nutrient needs of a system of plants.
But there were limits to the amount of nitrogen that could be obtained from natural processes for high-intensity agriculture. If your goal was to maximize yields, especially of protein, you needed a way to not only replace what you were taking out of it, but actually juice the topsoil with extra nitrogen. The question was: how do you take some of the abundant N 2 in th air and convert into a nitrogen compound that is easily used by plants?
Up next, the story of how chemical fertilizer, a double-edged sword if there ever was one, was created. I’ll give you a hint–we used fossil fuel.
So, this is a post in a continuing series dedicated to exploring new fertilizer technologies that could reduce their environmental impact and energy usage while increasing food security.
See Also:
In Search of New Fertilizer Tech (No, Really)
Image: flickr/weaselmcfee
