Due to the growing costs of agricultural production and the need to protect the environment, there has been a need to intensify activities leading to an increase in the effectiveness of natural biological processes. These measures should increase the biodiversity of the environment, enable the adaptation of microorganisms and the protection of plants and soils against the background of the concept of sustainable agricultural development. The soil is an important environment in which many elements are transformed, including nitrogen necessary for the proper yielding of plants. The aim of the article is to present the microbiological aspect of nitrogen transformation, starting with a review of historical findings and then to discuss the progress of the latest developments that have contributed to a detailed understanding of the biochemical reactions occurring during nitrogen transformation in soil. Moreover, the aim of the study is to present the current state of knowledge on the dynamics of nitrogen uptake and conversion by various species of microorganisms and the relationship between the activity of nitrogen microorganisms and nitrogen uptake by plants. The article also includes the latest information on the possibility of using microbiological biostimulants supporting plant growth (PGPR) and protection against the effects of phytopathogens.

The aim of the conducted research was to assess the effectiveness of the nitrification process, at different concentrations of ammonium nitrogen, in biologically treated wastewater in one of the largest municipal and industrial wastewater treatment plants in Poland. The studies also attempted to acclimate nitrifying bacteria to the limited concentration of ammonium nitrogen and determined the efficiency of nitrification under the influence of acclimated activated sludge in the biological wastewater treatment system. The obtained results indicate that the concentration of ammonium nitrogen above 60.00 mg·dm⁻³ inhibits nitrification, even after increasing the biomass of nitrifiers. The increase in the efficiency of the nitrification process in the tested system can be obtained by using the activated sludge inoculated with nitrifiers. For this purpose, nitrifiers should be preacclimated, at least for a period of time, allowing them to colonize the activated sludge. The acclimated activated sludge allows reducing the amount of ammonium nitrogen in treated sewage by approx. 35.0%. The process of stable nitrification in the biological treatment system was observed nine days after introducing the acclimated activated sludge into the aeration chamber.

Increasing consumption of processed potatoes and consumer preference for buying potatoes washed and packed in transparent packages are a reason for increasing quality standards for potatoes. Processing and trade require potato tubers with smooth skin and without signs of disease, such as common scab, black scurf, and silver scurf. It is necessary to introduce protective measures to reduce the growth of pathogens causing these diseases and, at the same time, are safe for the environment and the consumer. To meet these requirements, the effects of application to soil and treatment of seed potatoes in the following solutions were examined: biological control agents (BCAs): Pythium oligandrum (BCAPo), Bacillus subtillis str. QST 713 (BCABs); microbial soil additives (MSADs): Efficient microorganisms (EM), UGMax soil conditioner, Biogen Rewital (BR); plant growth promoter (PGP): Ecklonia maxima (PGPEm) for the infection of the tubers by Streptomyces scabies (S.s), Rhizoctonia solani (R.s) Helminthosporium solani (H.s) and potato yield. Average Disease Severity Index (DSI) for common scab (S.s) 62.0%, black scurf (R.s) 57.88%, and silver scurf (H.s) 54.24%, obtained from three growing seasons, indicate their significant economic importance. The bio-preparations used significantly reduced their intensity. The effectiveness of protection for individual pathogens varied and was highly dependent on hydrothermal conditions. The analyzed preparations showed E between 8.0% and 50.8% against S.s. However, a stronger effectiveness was found in relation to H.s (12.9–56.6%) and R.s (19.5–69.2%). In years with water deficit, PGPEm and MSADs are more effective than BCAs in protecting potato tubers from skin diseases and contribute to higher yield increases. There was a significant negative correlation between the total DSI and the potato tuber yield.

Water reuse is now becoming a global necessity. However, one of the drawbacks in releasing wastewater into the environment is some persistent pollutants that are not completely removed in wastewater treatment plant. Residual bacteria and antibiotics in the inflowing wastewater can contribute to the antibiotic resistance spread in the aquatic environment. This study determined the effectiveness of activated sludge process for fecal coliform bacteria elimination, and also the Escherichia coli resistance to antimicrobial agents as erythromycin, azithromycin, clarithromycin, ofloxacin, ciprofloxacin, trimethoprim, and metronidazole in treated wastewater. The research was carried out using the membrane filtration technique, and the susceptibility of isolates to antimicrobial agents was tested by the disc diffusion method. The concentrations of fecal coliform bacteria and Escherichia coli differed significantly depending on the seasonal period in which it was carried out. Despite up to 99% reduction in the number of sanitary indicators in biologically treated wastewater, 89% of E. coli isolates resistant to the tested antibiotics was found, while 100% of the isolates were susceptible to metronidazole. Most of the isolates showed resistance to trimethoprim, and the fewest isolates were resistant to ofloxacin, indicating that some strains may react differently to antibiotics.

COD is an arbitrary indicator of the content of organic and inorganic compounds in wastewater. The aim of this research was to determine the effect of COD of industrial wastewater on the nitrification process. This research covered wastewater from acrylonitrile and styrene–butadiene rubbers, emulsifiers, polyvinyl acetate, styrene, solvents (butyl acetate, ethyl acetate) and owipian^® (self-extinguishing polystyrene intended for expansion) production. The volume of the analyzed wastewater reflected the active sludge load in the real biological treatment system. This research was carried out by the method of short-term tests. The nitrification process was inhibited to the greatest extent by wastewater from the production of acrylonitrile (approx. 51%) and styrene–butadiene (approx. 60%) rubbers. In these wastewaters, nitrification inhibition occurred due to the high COD load and the presence of inhibitors. Four-fold dilution of the samples resulted in a two-fold reduction in the inhibition of nitrification. On the other hand, in the wastewater from the production of emulsifiers and polyvinyl acetate, a two-fold reduction in COD (to the values of 226.4 mgO₂·dm⁻³ and 329.8 mgO₂·dm⁻³, respectively) resulted in a significant decrease in nitrification inhibition. Wastewater from the production of styrene, solvents (butyl acetate, ethyl acetate) and owipian^® inhibited nitrification under the influence of strong inhibitors. Lowering the COD value of these wastewaters did not significantly reduce the inhibition of nitrification.

The basic foundation of plant production consists in plant protection treatments, which largely shape the quality of plant raw material intended for the food industry. Due to its long growing season, horseradish requires more treatments than average. Intensive protection based on synthetic pesticides favours the accumulation of their residues in plants and generates serious environmental problems. We have examined the effect of chemical protection and its reduced variant as well as three variants of biological protection, differentiated in terms of preparations used for seedlings treatment (Pythium oligandrum, Bacillus subtilis, and Ecklonia maxima), on the content of dry matter, protein, fat, carbohydrates, and the disease severity index (DSI) of Verticillium wilt of horseradish roots. The quantitative and qualitative changes in the microorganism communities associated with this disease were determined. Thirty-four species of fungi and Globisporangium irregulare have been shown to contribute to the pathogenesis of Verticillium wilt. The following were found with the highest frequency: Verticillium dahliae (14.37%), G. irregulare (6.87%), Ilyonectria destructans (6.73%), Fusarium acuminatum (6.53%), Rhisoctonia solani (6.75%), Epicoccum nigrum (5.56%), and Alternaria brassicae (5.36%).We found that water deficit promotes the increase of DSI and reduces the number and richness of fungal species isolated from diseased roots. The variant of biological protection with treatment of seedlings of E. maxima extract and with reduced chemical protectionin dry seasons give the best protective effects. Under conditions of optimal water supply, biological protection (P. oligandrum) is more effective than chemical protection. Biological protection increases biodiversity in the population of microorganisms that contribute to blackening of the conductive bundles of horseradish roots. There is a significant negative correlation between the number of isolated microorganisms and the DSI value. Increasing the number of the CFUs is accompanied by a reduction in the symptoms of Verticillium wilt of horseradish roots. Biological protection in years with sufficient water supply results in a significant increase in the content of dry matter, protein, and carbohydrates in horseradish roots. Under the influence of protective treatments, the ash content in the roots and its alkalinity decrease.