The Haber-Bosch process has transformed agriculture. Developed by German scientists Fritz Haber and Carl Bosch, the technique was first used to produce ammonia on an industrial scale in 1913. Since then it has provided farmers with a ready source of reactive nitrogen, which can be applied to crops directly and significantly increases yield. Farmers have enthusiastically embraced this “wonder-food”; since the 1960s the use of nitrogen fertilizers has increased nine-fold. But the resulting agricultural gains are also associated with substantial environmental losses.

“About 1% of applied nitrogen is released into the air as nitrous oxide, a powerful greenhouse gas with 300 times the warming power of carbon dioxide,” said Nathan Mueller of Harvard University, US. Meanwhile, making fertilizer using the Haber-Bosch process accounts for around 2% of global energy consumption. And the negative impact of nitrogen fertilizer on water quality is clear from the anoxic “dead-zone” that has developed in the Gulf of Mexico as a result of over-use of fertilizer in the United States.

Cutting nitrogen pollution could have major environmental benefits. With this in mind, Mueller and colleagues have used “crop-input” models to investigate how nitrogen fertilizer application could be minimized while still maintaining crop yields. By taking into account regional climate variations and the responses of various crops to differing levels of nitrogen application, they were able to see which regions of the world were under- or over-applying nitrogen fertilizer, and calculate how fertilizer application could be optimized.

More efficient use of nitrogen fertilizer on cereal crops could halve the amount used, without any decline in overall global food production, the team found.

“It’s possible to increase agronomic efficiency by applying fertilizers in an appropriate amount at the right time and place,” explained Mueller, whose findings are published in Environmental Research Letters (ERL). “High-tech options are also becoming available, with precision management systems and controlled-release fertilizers.”

The scientists also showed that redistribution of fertilizer has the potential to increase global crop yields by as much as one third. Specifically, China, western Europe, northern India and the United States could all reduce fertilizer application without major loss of yield. Meanwhile, modest increases in fertilizer use across sub-Saharan Africa and Eastern Europe would bring valuable yield rises.

“Since the response of crop yield to nitrogen is nonlinear – with greater yield gains for additional nitrogen at low application rates – the net result could be similar total crop production with much less total nitrogen application,” explained Mueller.

Achieving these changes in fertilizer use may not be easy but there are already some encouraging efforts. “Various regional efforts are underway,” Mueller told environmentalresearchweb. “For example, EU policies, including the Nitrates Directive, have stimulated increased efficiency and provide a model moving forward. And there is incredible work being done in China to demonstrate higher-efficiency systems through a countrywide network of 12,000 demonstration plots. The hope is that this distributed network will be able to reach the millions of small farmers throughout China.”

If we are clever about it, it should be possible to reduce the environmental impact of fertilizers at the same time as increasing food production: a win-win situation for all.

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