The Impact of Exogenous Organic Matter on Wheat Growth and Mineral Nitrogen Availability in Soil

Application of exogenous organic matter (EOM) to soil enriches it with micro- and macro-elements necessary for the proper growth and yield of crops. One of these elements is nitrogen, which is a major nutrient affecting crop production worldwide. Therefore, the aim of our study was to assess the impact of various EOM treatments (with and without mineral fertilization) on wheat yield characteristics and the dynamics of mineral nitrogen release. This study was conducted as a pot experiment using three soils characterized by different physicochemical properties, which were collected from the Polish–Czech Republic transboundary area. A spring wheat (the Tybalt cultivar) was selected as the model test plant. The EOMs tested in the experiment included three soil amendments (animal meal, industrial compost, and digestate) characterized by different potential impacts on plant growth and development. The efficiency of the selected amendments was analyzed in two doses, set at 50% and 100% mineral nitrogen ratios (equivalent to 70 and 140 kg ha⁻¹, respectively). The content of mineral nitrogen (N-NH₄⁺ and N-NO₃⁻) in soils before sowing and after harvesting, and the quality and biomass of the wheat yield were determined. The application of an entire N rate in the form of EOM did not cause any decrease in the wheat yields or a clear diversification of the wheat biomass. However, the appropriate selection of rates and fertilizer combinations resulted in an increased amount of available nitrogen being introduced into the soil (a 9–31% and 17–38% increase of N-NH₄⁺ in soils before sowing and after harvesting, respectively, and a 4–63% and 10–34% increase of N-NO₃⁻ in soils before sowing and after harvesting, respectively), which resulted in an increase in grain weight, reflecting yield and grain quality (from 2% to 12% higher grain weight compared to the control). The applied EOMs were characterized by readily transforming forms of organic nitrogen into N-NH₄⁺ and further increasing the speed of its conversion into N-NO₃⁻, indicating the capacity of these treatments to act as substitutes for synthetic nitrogen fertilizers.