Consumption of Soil Nitrogen by Plants under the Application of a Mineral Fertilizer, Green Manure, and Biopreparation (the study involves 15N)

The use of soil nitrogen by spring wheat plants in sod-podzolic medium loamy soil enriched with a stable nitrogen isotope 15N was researched in a model experiment involving the application of ammonium nitrate and white mustard biomass and seed inoculation with associative nitrogen fixer Rhizoagrin. It is established that plants primarily consume nitrogen contained in the recently applied mineral fertilizer. After the application of white mustard biomass and seed inoculation with Rhizoagrin, spring wheat consumes soil nitrogen; after the combined application of the above components and ammonium nitrate, spring wheat consumes both soil nitrogen and nitrogen contained in the fertilizer. The plant biomass accumulation increases predominantly due to nitrogen contained in the recently applied mineral fertilizer, regardless of whether it was applied separately or in combination with green manure and seed inoculation with the biopreparation. The increase in the plant biomass accumulation reaches 14–28% in comparison with the control variant (no fertilizers). After the application of the nitrogen fertilizer, either separately or in combination with green manure and the biopreparation, the concentration of nitrogen in spring wheat increases by up to 1.5 times. A clear upward trend is observed in relation to the nitrogen concentration in plants after the application of white mustard biomass and seed inoculation with Rhizoagrin. As a result, the total nitrogen accumulation in plants increases twofold after the application of the nitrogen fertilizer and by 1.2 times after the application of white mustard biomass and seed inoculation with the biopreparation. This is due to the presence of nitrogen compounds available to plants in the growing medium. The accumulation of 15N in plants characterizes the consumption of soil nitrogen by them. This parameter decreases after the application of the nitrogen fertilizer and remains equal to that in the control variant (no fertilizers) after the application of white mustard biomass and Rhizoagrin. This indicates that plants consume large amounts of mineralized soil nitrogen after the application of the two latter components and that nitrogen fertilizer is not a factor in the mineralization of soil organic matter. The application of white mustard biomass prior to spring wheat sowing and inoculation of its seeds with Rhizoagrin ensure that plants consume soil nitrogen in the initial vegetation period.