# Digestate Management and Processing Practices: A Review
## 7 Fertilization Value of the Digestate  
Modern agricultural production is becoming increasingly intensive while the demand for the development of new fertilizers, that can help overcome obstacles in global agricultural production, is constantly increasing. The increasing intensity of agricultural production, along with the expansion and development in the food industry, leads to an increase in the amount of organic waste produced globally. To produce a high-quality organic fertilizer sustainably, organic waste needs to be managed as a valuable resource that could significantly support agricultural production. The most appropriate and valuable way to use or reuse organic waste is through fertilization. Some of the potential benefits of using organic wastes are the possible improvement of soil fertility, provision of plant nutrients in agricultural production, and increase in soil organic content [192]. Considering climate change and fossil fuel constraints, DG is considered an environmentally friendly fertilizer that can be sustainably used for food production [193]. It can be used in various types of agricultural productions and can reduce dependence on inorganic fertilizers. However, its application can sometimes cause nitrate and phosphate pollution of groundwater. Therefore, the selection of the method of DG application is crucial and it determines whether DG is a solution or a problem for the environment and agricultural production. When applied adequately, DG can maintain grassland productivity, reduce environmental impact and increase biomass yields [64]. Ref. [194] conducted six-year field experiments at two challenging sites in southwestern Germany in which they evaluated the impact of (a) mineral fertilizer, (b) combined solid DG fraction and mineral fertilizer, (c) solid DG fraction, (d) combined liquid DG fraction and mineral fertilizer, and (e) liquid DG fraction on silage maize biomass yield, perennial grassland and in intercropping of clover grass and tritcale. The objective of the study was to determine whether separated DG can supplement or replace mineral fertilizers and what influence it has on long-term yield performance in different biomass cropping and fertilizer systems. The results showed that the application of mineral fertilizer combined with the liquid fraction of DG resulted in the highest biomass yields in all cropping systems. In contrast, fertilization using only the solid fraction of the DG resulted in the lowest yields in all plots. Yields in plots fertilized with the solid fraction of DG were not significantly different from the control. The authors concluded that the use of separate biogas DG gave similar results to mineral fertilizers and had comparable results. Although in some systems (intercropping) it is possible to completely replace mineral fertilizers with DG, the best results are obtained with the application of mineral fertilizers combined with DG, which can reduce the use of mineral fertilizers by up to 66%. Mineral N from DG is generally poorly immobilized in the soil, due not only to the low C/N ratio but also to the content of highly stable OM. When the DG is incorporated into the soil, the NH\({}_{3}\) ions undergo an immediate nitrification process. When comparing different types of DGs, the DG produced after AD of sewage sludge has a high rate of nitrification and mineralization of OM and its capacity to supply the plants with mineral N is comparable to the urea. Because of its characteristics, it can at least partially, substitute or complement synthetic N fertilizers and reduce their use in agricultural production [195]. Application of DG can have a stimulating effect on soil C matter decomposition supplying the soil with an additional pool of readily available mineral N. However, it also can cause excess NH\({}_{3}\) volatilization and dispersal of oxidized forms of N through nitrate (NO\({}_{3}\)) leaching or nitrous oxide (N\({}_{2}\)O) emissions.