Cow Manure Makes Dandy Organic Fertilizer, Say Cornell Researchers

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Cows are an environmental nightmare. Not only do they take up lots of space that might be better used for solar panels, they emit copious quantities of methane from both ends. Where there are cows, there are no trees to absorb carbon dioxide from the atmosphere. In fact, large tracts of the Amazon rainforest have been chopped down to make room for more cows to meet the insatiable appetite of humans for the meat we get from slaughtered cows.

Cows have another problem. They turn millions of tons of feed into millions of tons of excrement, popularly known as cow flops or meadow muffins that many young boys enjoy flinging at each other in the pasture before dinner. As John Denver would say, “Thank God I’m a country boy!”

Unfortunately, there is far more manure than there are fields to spread it on these days, so the stuff is stored in liquid form in large lagoons, which is okay until the retaining wall breaks. In some places, farmers have learned to cover their lagoons with tarps that capture the methane created when the stuff ferments and turn it into what truly is natural gas, as opposed to the unnatural stuff that frackers force from the Earth using toxic chemicals under intense pressure.

Researchers at Cornell University say they have devised a new way to convert bovine waste into sustainable fertilizer to replace the concoction of chemicals farmers use on their crops today. They say that heating it at between 700 and 1200 degrees F in the absence of oxygen– a process known as pyrolysis — retains valuable nutrients from dairy lagoons while transforming them into a manageable, ecologically friendly biochar.

“Manure is usually a liquid problem and it has increasingly been an issue of disposal,” says Professor Johannes Lehmann of the Cornell College of Agriculture and Life Sciences. “Using pyrolysis of solid manure and retention of nutrients from the liquid onto the biochar, we can create a fertilizer from waste. That’s a marketable commodity. Farmers can spread this fertilizer when the field crops need it, instead of when the farmers need to get rid of manure.”

According to Cornell, “Biochar is a solid, charcoal-like material formed by heating biomass in the absence of oxygen in a process known as pyrolysis. Though not a fertilizer, biochar — when applied to soil — boosts fertility by helping to retain water in the soil when it is dry, and it helps to promote drainage when conditions are wet and retain soil nutrients.”

Commercial fertilizer made of nitrogen, phosphorus, and potassium is created using carbon inputs like natural gas, sulfur, coal, and rock deposits. If agriculture can recycle nitrogen, Lehmann says, farming can reduce the carbon input that comes from fossil fuel.

Doctoral student and lead author Leilah Krounbi then figured out a way to enhance the biochar. First she treated it with carbon dioxide (of which humanity has an inexhaustible supply) and then used it to grow radishes and tomatoes. Those vegetables grew up to 35% larger and had an 83% greater nitrogen uptake compared with manure biochar alone.

“Once we make a dry fertilizer out of what was once a liquid problem, it is no longer an issue of disposal,” says Professor Lehmann. “It’s safe because the solids are pyrolyzed. There are no pathogens, no hormones, or antibiotics residues or any other material that could contaminate soil or water.”

Nitrogen management is a major challenge throughout the farming world. In New York State, for example, dairy manure waste production averages 12.8 million metric tons annually, enough to easily fertilize the state’s 43,000 acres of corn. A farmer who grows 200 acres of corn spends about $28,000 annually for commercial fertilizer. Meanwhile, a dairy farmer with 550 cows spends about $25,000 annually on manure storage, the researchers say.

You can see where this is going, right? “Coupling the local excess of manure nutrients with regional fertilizer needs could help farmers save money and alleviate environmental issues,” Krounbi said. If all the available dairy waste in New York were pyrolyzed, that would yield up to 42,232 metric tons of nitrogen with a commercial value of $21.5 million annually. The best part it, that would meet up to 82% of New York State’s nitrogen fertilizer needs and substantially reduce environment pollution.

“You’re reducing the volume of the solid waste product that has 90% water and reducing it to zero water,” Lehmann said. “If we retain nutrients from the liquid as we have shown in this study, you’re going from these huge lagoons that are noticeably emitting odor and climate gases such as methane and reducing that footprint by an order of magnitude. That’s a huge saving all around.”

The research was funded by the National Science Foundation, the US Department of Agriculture and Cornell Atkinson.


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Steve Hanley

Steve writes about the interface between technology and sustainability from his home in Florida or anywhere else The Force may lead him. He is proud to be "woke" and doesn't really give a damn why the glass broke. He believes passionately in what Socrates said 3000 years ago: "The secret to change is to focus all of your energy not on fighting the old but on building the new."

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