This study evaluated the effect of one-time phosphate fertilization on the soil microbiota, its cycling of phosphorus (P) and grass growth. Soil columns were established in a greenhouse using a P-limited Irish soil (index 1), planted with Lolium perenne and fertilized with 0 (control), 5 (quarter), 10 (half) and 20 (full)kgPha as inorganic phosphate. Only traces of phosphate in soil solution were detected over the 14week experiment, even after phosphate fertilization. Grass dry matter yield between treatments was not significantly different. Full phosphate fertilization significantly reduced the arbuscular mycorrhization (AM) rate, bacterial- and fungal-feeding nematode population, bacterial phoD gene abundance, but increased alkaline and acid phosphatase activities at the time of harvest. Full and half P treatments significantly shifted the bacterial, fungal and AM community structures compared to the control. Furthermore, the control had a significantly higher relative abundance of bacterial genera including Bacillus, Bradyrhizobium, Paenibacillus, Nocardioides and Balneimonas, that have been associated with P mobilization in the past, when compared to the full phosphate treatment. These results suggest that a positive effect of a single phosphate application on plant growth in a soil can be cancelled out by its negative effect on the soil microbiota and their ecosystem services.

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Enhancing the role of the soil microbiota in plant phosphorus (P) and sulfur (S) supply through application of organic fertilizer could reduce dependencies on non-sustainable synthetic fertilizers. To compare the effects of organic/inorganic fertilizers on the soil microbiota, soil columns with Lolium perenne (ryegrass) were setup in a greenhouse and amended with an inorganic fertilizer, cattle slurry (organic), or urea (P-and S-free control). Ryegrass rhizosphere of the slurry treatment had significantly higher abundances of bacterial-feeding nematodes, mycorrhizal colonization, cultivable heterotrophic bacteria, phosphonate-and sulfonate-utilizing bacteria, arylsulfatase activity, available P and Variovorax asfA gene copies compared to the inorganic and urea treatments. Phosphomonoesterase activities, and gene abundances involved in organic P and S transformations (phoD, phoC, Burkholderia & Polaromonas asfA) were similar in all treatments. Grass dry matter yield, shoot uptake of N, P and S were significantly higher in the inorganic treatment compared to the urea and slurry treatments. Community compositions differed significantly between the three fertilizer treatments and included the bacterial, alkaline phosphomonoesterase-producing bacterial, fungal, AM fungal, and nematode communities. Bacteriodetes were found in higher relative abundance in the organic treatment while Acidobacteria were more abundant in the urea and inorganic fertilizer treatments. These community shifts correlated significantly with grass dry matter yield, uptake of N, P and S, mycorrhizal colonization, enzyme activities, abundances of bacteria and bacterial-feeding nematodes. We concluded that organic fertilization promoted soil microbes and nematodes which have the potential to support sustainable plant growth, provided that the overall nutrient requirements are met.

Various nutrient recycling technologies are currently under development in order to alleviate the dependency of non-renewable raw material for the production of mineral phosphorus fertilizers commonly used in agriculture. The resulting products, such as struvites and ashes, need to be assessed for their application as so-called recycling-derived fertilizers (RDFs) in the agricultural sector prior to commercialization. Here, we conducted a short-term (54 days) trial to investigate the impact of different phosphorus fertilizers on plant growth and the soil P cycling microbiota. Lolium perenne was grown with application of superphosphate (SP) as inorganic fertilizer, two ashes (poultry litter ash (PLA) and sewage sludge ash (SSA)), and two struvites (municipal wastewater struvite (MWS) and commercial CrystalGreen® (CGS)) applied at 20 and 60 kg P ha−1 in four replicates. A P-free control (SP0) was also included in the trial. Struvite application increased plant dry weights, and available P acid phosphatase activity was significantly improved for struvites at the high P application rate. The ash RDFs showed a liming effect at 60 kg P ha−1, and PLA60 negatively affected acid phosphatase activity, while PLA20 had significantly lower phoD copy numbers. P mobilization from phosphonates and phytates was not affected. TCP solubilization was negatively affected by mineral SP fertilizer application at both P concentrations. The bacterial (16S and phoD) communities were only marginally affected by the tested P fertilizers. Overall, struvites appeared to be a suitable substitute for superphosphate fertilization for Irish L. perenne pastures.

Sulfate fertilization supports growth of ryegrass in soil columns but changes microbial community structures and reduces abundances of nematodes and arbuscular mycorrhiza Article Type: Research Paper