Different Response of Carbon and P-Related Soil Properties toward Microbial Fertilizer Application

While some studies regarding the effect of biofertilizers on plants, including their yield and quality, less is known about how they affect the soil properties, especially the microbial and enzymatic properties. Biofertilizers are promising for enhancing the nutrient availability in agricultural soils and reducing the reliance on inorganic fertilizers. The aim of this four-year-long field experiment was to assess the influence of the use of UGmax biofertilizer, which contains bacterial strains enhancing the soil phosphorus availability, e.g., the Pseudomonas spp. strains from Azotobacter and Penicillium genera, on the soil P forms and acid and alkaline phosphatase activity (AcP, AlP) in the surface soil horizon (Ap). Winter wheat was cultivated in 2005, 2006, and 2008, while winter rapeseed was cultivated in 2007 in a research area (2 hectare) that was selected for the investigation. These plants were selected because they are the main agricultural crops in Poland. UGmax was applied in three successive years after the plants had been harvested. One dose of the biofertilizer (0.7 L per hectare) was applied after the harvesting of wheat had been harvested (2005–2007), while the second dose (0.3 L per hectare) was applied as a top dressing in the spring, when the plants were beginning to grow (2006–2008). Forty soil samples were taken in 2005 (the control year without the application of UGmax). In the following years (2006–2008), 20 soil samples were taken from the area after the UGmax had been applied in the previous year, as well as 20 soil samples from the control area. A grid soil sampling technique (40 m × 25 m) was used to assess the changes in the soil properties across both of the studied areas. The soil samples were taken from the surface (Ap) horizon. Only at the end of the experiment (2008) did the application of UGmax remarkably increase the organic carbon (Corg) and total nitrogen (Nt) content, while the microbial biomass carbon (MBC) content was notably higher in the field with UGmax than in the control. The available P content (Pavail) was significantly higher in the field with UGmax compared to these without the biofertilizer in 2006 and 2008, while no considerable relation was noted for the total phosphorus (Ptot) and water soluble P (Pwater) content in any of the study years. Over the entire period of the experiment, the AcP and AlP were notably lower in the soil samples that were collected from the UGmax field compared to that of the contro