Thursday, 29 January 2015

Climate change: and farming with less nitrogen

When we think of 'greenhouse gases', the one that comes to mind most readily is carbon:
Futures Forum: Climate change: the great carbon offsetting scam
Futures Forum: Climate change: IPPR's Low Carbon Manifesto: "there should be a shift in focus away from large-scale generation to energy efficiency, new sources of finance for low-carbon infrastructure and a recognition of the huge role that the regions play in low-carbon energy generation."
Futures Forum: Climate Change: "It appears the more carbon we emit, the less we want to believe we’re contributing to the problem."
Futures Forum: Climate change: "The implication of no immediate action is worryingly clear."

... followed perhaps by methane:
Futures Forum: Good gas, bad gas........ Anaerobic Digestion and Methane from Livestock...

But what about nitrogen?

The large increase in the use of nitrogen fertilizer for the production of high nitrogen consuming crops like corn has increased the emissions of nitrous oxide.

Although nitrogen fertilizer is essential for profitable crop production, the development of practices for more efficiently using nitrogen fertilizer has the potential to significantly reduce nitrous oxide emissions while also reducing production costs and mitigating the nitrogen contamination of surface and ground waters.

Global warming – agriculture's impact on greenhouse gas emissions | Ag Decision Maker
BBC - Weather Centre - Climate Change - Nitrous Oxide
Nitrogen - The Bad Guy of Global Warming - The Naked Scientists
Anthropogenic nitrogen plays a double role in climate change

Fertilizer produces far more greenhouse gas than expected

Farmers’ overuse of nitrogenous additives may explain puzzling emissions


With an overload of fertilizer, soil microbes on farms may belch unexpectedly high levels of nitrous oxide, a greenhouse gas with 300 times as much heat-trapping power as carbon dioxide. The finding may help explain why agricultural nitrous oxide emissions are much higher than some scientists had predicted and could give clues for how to curb farm pollution.

Soil microbes have long been known to convert nitrogen-rich crop fertilizers, including manure and synthetic fertilizers, into nitrous oxide. After more than 1,000 field experiments, climate scientists calculated in the mid-2000s that the dirt dwellers spew about one kilogram of the greenhouse gas for every 100 kilograms of fertilizer, or roughly 1 percent. Researchers generally thought that emissions would scale up linearly: doubling fertilizer would double the emissions of gas.

But the predictions didn’t match up with real-world numbers. Estimating regional and global fluxes of atmospheric nitrous oxide levels a few years ago, researchers pegged the microbial conversion of fertilizer to gas at somewhere between 1.75 and 5 percent. Either the initial calculations were off or there were unknown sources of nitrous oxide, says biogeochemist Phil Robertson of Michigan State University in East Lansing. The latter was unlikely, he adds.

From cornfield experiments in Michigan in 2005, Robertson and colleagues found that the relationship between the amount of fertilizer and production of greenhouse gas is not always linear. When farmers apply larger amounts of fertilizer than initially tested, the relationship appears exponential — applying 200 kilograms of fertilizer could result in four kilograms of gas, for instance. Most of the original field experiments, he says, didn’t look at microbial gas conversion with excess fertilizer, far more than crops need. In such situations, the crops take up as much nitrogen as they can, and the rest goes to soil microbes, Robertson says. “They effectively go to town on that nitrogen,” he says.

Fertilizer produces far more greenhouse gas than expected | Science News

Does climate change affect soil? | Soils Matter, Get the Scoop!

A UK Parliamentary Committee has just published a report looking at reducing the amount of nitrogen we use in farming today:

Emissions from Crops - Parliament UK

With a useful overview from the RuSource pages:
GHG emissions from crops - Arthur Rand Centre

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