Fertilizer addition effect of novel recycling fertilizers from human excreta in a pot experiment with maize (Zea mays L.)

Recycling nutrients from human faeces is a practicable and effective process in terms of the circular economy. To test this, we carried out a pot experiment with a hygienized human faeces compost (HHFC) and a nitrified urine fertilizer (NUF) made from contents of dry toilets to determine the short‐term fertilizer addition effect. HHFC variants were created in increments equivalent to 10, 20, and 30 t ha−1 dry matter weight (DM) and as joint fertilizer application of HHFC and NUF. For the classification of the fertilizer addition effect, soluble concentrations of nitrogen, phosphorus, and potassium in the soil as well as contents in the plant (Zea mays L.) were analysed after a trial period of 8 weeks. Above‐ground biomass, plant height, and chlorophyll content of the leaves were also assessed. The sole compost variants showed no to slightly higher DM yields than the control, whereas the combined compost urine fertilizer variant achieved around 80% of the DM yield of the mineral‐fertilizer applied reference treatment. The soil's total nitrogen storage is significantly increased in our experiment by the addition of HHFC. The concentration of soluble phosphorus in the soil increases significantly with increased compost applications. However, in the combined compost urine fertilizer variant, sufficient nitrogen supply results in a low level of soluble phosphorus because of high plant biomass production. This trend is reflected in the phosphorus content of plant material. HHFC is considered a good phosphorus fertilizer, which is also confirmed in this experiment. A similar picture emerges for the supply of potassium from HHFC. Although the liquid urine fertilizer (combined with HHFC) does not achieve the DM yield of the mineral reference variant in the early phase of plant growth, it has clear advantages in supplying the crop with nitrogen. This study shows that the recycling of nutrients from human faeces is a potential strategy for conserving finite resources and promoting energy‐efficient agricultural practices in line with the circular economy.