Long-term soil health effects of human urine and other bio-based fertilizers: A comprehensive field study

Urban Farm DB summary

Using a long-term field trial (the CRUCIAL experiment) running for more than 20 years in Denmark, this study compared the long-term effects of bio-based fertilizers (BBFs) — compost, sewage sludge, cattle slurry, and human urine — against conventional mineral NPK fertilizer on soil physical, chemical, and biological properties. Mineral NPK fertilizer supported crop productivity and improved certain soil properties but did not deliver the broader soil health benefits of organic amendments; compost and sewage sludge notably increased soil organic carbon, cation exchange capacity, porosity, water content at field capacity, and microbial activity while reducing bulk density and clay dispersibility. Human urine produced a nitrogen fertilizer effect on crop yield comparable to NPK, but showed a higher sodium adsorption ratio than NPK and a negative trend in bulk density (though values stayed below critical thresholds), indicating a need for complementary organic matter input, and carbon-rich bio-based fertilizers reduced crop production per unit of nitrogen applied.