Assessment of Recycling-derived Fertilizers as an Alternative to Mineral Fertilizers – Effects on the Soil Microbiome

Phosphorus (P) is an essential macronutrient for all living organisms and is applied as fertilizer in agroecosystems to improve crop growth. Recycling-derived fertilizers (RDFs) have been developed for nutrient recovery from Europe’s largest waste streams as a sustainable alternative to this finite resource. The impact of four RDFs (two ashes, two struvites) on the soil microbiome in comparison with a P-free control and triple super phosphate (TSP) as mineral fertilizer was investigated in a pot trial and a subsequent microcosm trial (subset of samples). For both experiments perennial ryegrass was cultivated for 54 days. The pot trial was conducted at P fertilization rates of 20 and 60 kg P ha-1 in quadruplicates. After the pot harvest the bulk soil was stored until the microcosm trial was conducted, using the control, TSP and the two ashes at 60 kg P ha-1 in six replicates. Pot trial results showed highest P bioavailability from struvites at high P rates, also resulting in higher biomass yield on average. Furthermore, P solubilization capabilities from tri-calcium phosphate was enhanced in the RDFs treatments, while the TSP treatments were negatively affected. For the microcosm trial, most probable number (MPN) analysis showed that phytate-utilizing bacterial abundance was significantly increased in one of the ashes and had also remained higher in the RDF treatments after storage. Understanding the effects of recycling-derived fertilizer application on the soil P cycle is vital for developing a more sustainable agriculture.