Responses of soil microbiota and nematodes to application of organic and inorganic fertilizers in grassland columns

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 set up 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, and Polaromonas asfA) were similar in all treatments. Grass dry matter yield and shoot uptake ofN, 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 phosphomonoesteraseproducing
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.