Living on air I 15 Pulled out of thin air Adding nutrient nitrogen Let’s go back to our little boat bobbing around on the ocean. We’re surrounded by an endless amount of water, and yet we’re thirsty. Our water bottle is empty. Fortunately it starts to rain – but not enough to fill our bottle. We have to come up with something clever. The same is true of nitrogen. We are surrounded by it, and yet we cannot consume it. To do that, we first have to convert it to nutrient nitrogen. The amount of nutrient nitrogen available in natural sources (lightning strikes, soil bacteria) has always been small, but until quite recently it was enough to feed the world population. That was largely thanks to farmers, who are preeminent nitrogen experts. Intent on improving their crops and increasing their harvests, farmers started using nutrient nitrogen many centuries ago, in the form of bird droppings, farmyard dung, and compost. They also let fields lie fallow to “save up” nutrient nitrogen.
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