Since the 19th century, phosphorus has been used as a fertilizer in agriculture to help plants grow and thrive. To do this, the material has to be mined or artificially produced, which consumes resources. In order to save resources, the recycling of human faeces can be considered. However, due to the Fertilizer Ordinance, this may only be used for research purposes and not in agriculture. A team from Humboldt-Universität zu Berlin (HU) has now provided new data to adapt the regulation.

Faecal compost as an effective phosphorus fertilizer

In a three-year series of experiments, the research team tested novel agricultural fertilizers on maize plants for the first time: They were treated with compost made from human faeces and a liquid fertilizer derived from human urine. The starting material came from dry toilets. The excrement was heated in a container for seven days and then composted. The results of the study showed that the urine-based fertilizer proved to be an effective source of nitrogen, while the faecal compost was an effective phosphorus fertilizer. The phosphorus concentration increased both in the soil and in the plants. The result was similar for the potassium content. 

A basis for reassessment

According to the researchers, these results provide a data basis for re-evaluating the Fertilizer Ordinance. “Based on the data collected, we can say that these fertilizers, as natural products, can be a useful addition to the nutrient cycle in agriculture,” says Jan-Ole Boness from the Albrecht Daniel Thaer Institute of Agricultural and Horticultural Sciences at HU. Their demand: human excrement should also be included in the list of permitted source materials for fertilizers.

In a follow-up project, the research team would like to investigate further properties of the new recycled fertilizers, such as possible pollutant residues and effects on the climate.

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