Recycling-derived Phosphorus Fertilizers as a Sustainable Alternative to Triple Superphosphate Fertilizers

Microbial activity is adamant for the nutrient cycling in soil. Generally, mineral phosphorus (P) fertilizer is applied to soil to improve plant growth, however, significant amounts are immobilized quickly. Mineral fertilizer can cause soil degradation, affecting the microbial community. Alternative, recycling-derived fertilizers (RDFs) need to be evaluated as suitable replacement for finite mineral P fertilizer. The impact of four RDFs (two ashes, two struvites) on the soil microbiome in comparison with a P-free control and triple superphosphate (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. Struvites displayed highest P bioavailability at high P application rates in the pot trial, yielding higher biomass on average. Furthermore, P solubilization 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. Non-metric multidimensional scaling (NMDS) analysis of phoD illumina sequencing data showed significant separation between all treatments of the microcosm trial. Understanding the impact of RDF application on the soil P cycle is vital to sustainable agriculture.