Monday, July 4, 2022

Nitrogen footprint: high pollution and loss of resources due to manure

In Germany, manure is usually applied to arable or grassland areas without pretreatment. The nitrogen released has a negative impact on the environment.
Credit: Markus Breig, KIT

Factory farming for meat production harms the environment. In addition to the directly emitted methane, the spreading of liquid manure releases climate-damaging nitrogen compounds such as ammonia and laughing gas into the atmosphere. In addition, the groundwater is contaminated with nitrate via the liquid phase. Researchers at the Karlsruhe Institute of Technology (KIT) have now examined how the manure that is produced in livestock farming and is often used as fertilizer affects the nitrogen footprint. They have shown that the nitrogen pollution from manure from beef production is three or eight times higher than for manure from pork and poultry meat production.

Large quantities of nitrogenous fertilizers and animal feed are used in agriculture. A significant part of the nitrogen used is released into the environment unused, for example by washing out nitrate from arable soils or by ammonia emissions from animal husbandry. “It is known that meat production has a very negative impact on the global nitrogen balance. The Nitrogen footprint calculator So far, however, it has not shown what a large proportion of the amount of manure that is generated in it,” says Prantik Samanta from the Engler Bunte Institute - Water Chemistry and Water Technology at KIT. “At the same time, these amounts of nitrogen mean an enormous loss of resources. Because recovering nitrogen is very expensive in terms of energy. "The doctoral student and first author of the study has now examined together with colleagues how much nitrogen about manure in beef, pork and poultry meat production pollutes the environment and is lost as a raw material. In addition, they calculated how much energy would be needed to process the manure and recover nitrogen. Again, this could be made available specifically as fertilizer.

Largest nitrogen loss in beef production

"We have found that the nitrogen loss per kilo of meat can be calculated directly with a virtual nitrogen factor, or VNF for short," says Samanta. “The relationship between the total nitrogen intake and the corresponding nitrogen loss per kilogram of meat production is linear. "The VNF compares nitrogen loss with the nitrogen content in the meat. The greatest loss is reflected in the manure to be disposed of or treated. The results show that beef production has the greatest impact on the nitrogen footprint in most parts of the world. The nitrogen loss is three or eight times higher than for manure from pork and poultry meat production. The researchers attribute this to the high feed requirements and the high basal turnover of cattle. The nitrogen losses in pig and poultry meat production are more likely to be due to poor barn conditions than to feed and the digestion of the animals.

In their investigations, the researchers also compared several countries: “Japan releases the largest amount of nitrogen in relation to the meat consumed, followed by Australia. This is also due to the fact that the values are shifted if the country's export or import feed and meat on a larger scale,” said Samanta. “As a result, the amount of manure to be treated per kilogram of meat is also highest in Japan." The nitrogen loss from meat production is lower in the USA and Europe.

Price increases for meat due to high energy requirements

The researchers also calculated how much energy would be required to minimize the entry of nitrogen into the environment as much as possible. “When producing one kilogram of beef, 140 grams of ammonium nitrogen remain in the cattle manure. To regain this, we need seven kilowatt hours of energy. For comparison: Germans consume an average of around 29 kilowatt hours of electricity per week per capita,” the scientist points out. When treating one kilogram of pig and poultry manure, the energy requirement drops significantly to less than three or 0.8 kilowatt hours.

"Our results clearly show how high the energy consumption for the manure treatment would be in order to reduce the entire nitrogen footprint in animal husbandry," says Samanta. At the moment, this energy requirement is not taken into account when pricing: “If you include it, the meat price would have to increase by 0.20 to 1.50 euros per kilo, depending on the type of meat."

Original publication:
Prantik Samanta, Harald Horn and Florencia Saravia: Impact of Livestock Farming on Nitrogen Pollution and the Corresponding Energy Demand for Zero Liquid Discharge. MDPI Water

Source/Credit: Karlsruhe Institute of Technology

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