Evaluation of the Use of Biogas Plant Digestate as a Fertilizer in Field Cultivation Plant

Biogas production in an agricultural biogas plant is connected with generation of large amounts of postdigestion liquid as a result of anaerobic decomposition of plant debris. Due to its physicochemical properties, post-digestion liquid can be used as a fertilizer. A possibility of agricultural utilization of digestate as a fertilizer was investigated. Digestate obtained from an agricultural biogas plant was tested for the content of macroelements and heavy metals. The content of macroelements was also examined in the soil before and after digestate application. Digestate was used for in the cultivation of fodder winter rape and winter wheat. The content of macroelements as well as the content of protein in the grains of winter wheat fertilized with digestate were on the same levels as in the grains of wheat fertilized with mineral fertilizers. Similar tendency was also observed in winter rape grains. Digestate utilization as a fertilizer brings tangible benefits in agricultural production and can reduce the negative effects of mineral fertilization and contribute to development the sustainable agriculture. The study has shown that digestate can be used as a fertilizer. INTRODUCTION Biogas production from anaerobic decomposition has been highly developed in recent years. In this process, large amounts of liquid are also produced. Post-digestion liquid is rich in nitrogen and phosphorus. It is possible to utilize digestate as a fertilizer on farmland (Dębowski et al., 2016). A biogas plant located in agricultural areas should collect organic products from local farms. Farmers, on the other hand, in their efforts to ensure soil quality on their farms, should use digestate from local biogas plants as a fertilizer (Comparetti et al. 2013, Garfi at al. 2011, Kowalczyk-Juśko et al. 2015, Tao et al. 2014). Fermented biomass has the same or higher agricultural value than liquid manure since it contains more mineral components (including nitrogen) and less organic matter. Digestate also has undesirable properties, such as: smell, viscosity, considerable humidity and high content of fatty acids which are phytotoxic, this is why digestate can be pathogenic (Bustamante et al., 2014). The use of post-digestion liquid as a fertilizer brings substantial benefits for agriculture; the possibility of using fermented biomass as a fertilizer contributes to improved soil fertility and higher crop yields. The utilization of post-digestion liquid as a fertilizer leads to the reduction of the use of mineral fertilizers (Cecchi, Cavinato, 2015, Cai et al., 2016, Di Maria et al., 2013). The aim of this investigation is to examine the justifiability of digestate utilization as a fertilizer in field cultivation of biennial plants, and also compare the content of macroelements after fertilization with digestate and mineral fertilizers in winter rape and winter wheat cultivation.