Environmental science: The shape of nitrogen to come
Although Earth's atmosphere consists of nearly 80% dinitrogen (nitrogen gas, N2), most living organisms cannot use this form of the element and require it to be converted into usable forms, such as ammonia. Humans have long exploited the ability of leguminous crops to fix dinitrogen into usable reactive nitrogen compounds, improving soil fertility. But the amount of reactive nitrogen produced in this way is now greatly exceeded by that produced industrially. Together with nitrogen oxides, another form of reactive nitrogen produced as a by-product of combustion processes, nitrogen compounds released into the environment by human activity are weaving a web of unforeseen consequences. Liu et al. quantify in their paper in "Nature" the massive scale of these changes to the nitrogen cycle across China, which are a direct result of increases in human activities such as food production, travel and energy consumption.