Nitrogen balance: circular economy with urine | nd-aktuell.de

Urine contains important plant nutrients such as nitrogen and phosphorus. Accounting for one percent of the total wastewater volume, it is responsible for 70 to 80 percent of the nitrogen and 45 to 60 percent of the phosphorus in the wastewater. But as various field tests show, urine and feces could be usefully used as fertilizer.

The citizen science project Urban Cycles showed that recycled fertilizer made from urine works in hobby gardens. Coordinated by the Leibniz Institute for Vegetable and Ornamental Crops (IGZ), garden teams in Berlin fertilized their vegetables for a season with recycled fertilizer made from synthetic urine. Compared to control beds that were fertilized with nettle manure, horn shavings or not fertilized at all, the yields were higher. The experiments in hobby gardens will also be continued this year.

Dr. Schmidt explains the world

Stephanie Schoell

As a polymath of the nd editorial team, the science journalist Dr. Steffen Schmidt has an answer to almost every question – and if he doesn’t, he answers another one. All episodes can be listened to on: dasnd.de/schmidt

In a test with white cabbage in Großbeeren/Brandenburg, results were just as good with urine fertilizer as with fertilizer established in organic farming. In comparison, the yields of compost made from human feces are lower. His Study results The research team led by Franziska Häfner at the IGZ published it a year ago in the specialist journal “Frontiers in Environmental Science”.

The team planted white cabbage in three soils that differed primarily in their clay content. The fertilizers were applied individually, and there were also combinations of stool compost and urine fertilizer. The latter is based on artificial urine as a starting material and contains all the substances that can be found in human urine, such as urea, creatinine and salts.

Vinasse, a fertilizer approved for organic farming based on residues from the sugar and alcohol industries, was used as a comparison product. The most productive were plants fertilized with the urine fertilizers Aurin or Crop or with Vinasse on sandy soil with a low clay content. Here the yield was around 72 tons per hectare. The fertilizers made from human urine were therefore just as good as the fertilizers approved for organic farming. The combination of stool and urine fertilizer performed somewhat worse. The pure stool compost variant produced even lower yields.

The team examined the white cabbage for 310 substances and found only minimal traces of the drug carbamazepine. Nitrate-enriched urine fertilizers such as Aurin and Crop have enormous potential as fertilizers in agriculture, the scientists conclude. Their effectiveness is comparable to other fertilizers and they have a lower heavy metal load.

The combined use of nitrified urine fertilizer and fecal compost leads to slightly lower crop yields, explains Franziska Häfner. In the long term, however, it increases the carbon content of the soil and thus supports climate-resilient food production.

With proper processing and quality controls, up to a quarter of the synthetic mineral fertilizers used in this country could be replaced by recycling from human urine and feces, emphasizes the study leader. If the number of farm animals and the cultivation of fodder plants were reduced, even less artificial fertilizer would be necessary. The consumption of fossil natural gas would also decrease.

But how does urine get to where it is needed? For example, by collecting it in special toilets and processing it in a targeted manner. As part of the “Combined Regenerative Organic Food Production” project at the German Aerospace Center, for example, a filter system was developed that can produce a mineral fertilizer with a high nitrogen content from urine. This could be used to fertilize vegetables in a space greenhouse. When waste such as urine is recycled to produce food, the nutrient cycle is closed. What applies to long-term missions to Mars can also be important for survival on Earth.

However, urine fertilizers are banned in gardening and agriculture in this country. In view of the promising results, scientists are calling for their approval.

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