Urban Waste Fertilizer: Effects on Yield, Nutrient Dynamics, and PTE accumulation

Abstract Recycling nutrients contained in urban wastes to agriculture is essential in a circular society. This study simultaneously compares different recycled fertilizers (household waste compost, sewage sludge, human urine) with mineral fertilization and animal manures. Tested were their long-term effects on yield, nutrient budgets, potentially toxic element (PTE) accumulation, and nitrogen (N)/carbon cycle (a.o. N efficiency, N losses, soil carbon). Therefore, data from a long-term field trial and predictions from the soil-plant-atmosphere model DAISY were evaluated. Based on trial data, human urine performed similar to the mineral fertilization for yield, N efficiency (MEF = 81%), and nutrient budget, while sewage sludge and compost were more like animal manures with lower yields, N efficiencies (MEF 70% & 19% respectively) and higher nutrient imbalances, especially P and S surpluses. Compost and sewage sludge applications resulted in net PTE inputs. Yet, plant uptake and soil accumulation seemed neglectable. Model outputs predicted N losses of 34–55% of supplied N. Losses were highest for compost, followed by deep litter, manure, sewage sludge, human urine, mineral fertilization, and slurry. Nitrate leaching was the main loss pathway (14–41% of N input). Within the compost and straw-rich manure treatments, about 25% of applied N, were stored in the soil which was accompanied by an increase in soil carbon. The study suggests substitution of established fertilizers with recycled ones is feasible. Thereby each fertilizer has advantages and disadvantages, and thus should be utilized according to their strength or in mixtures.