The impact of biogas digestate typology on nutrient recovery for plant growth: Accessibility indicators for first fertilization prediction

In recent years, anaerobic digestion of organic waste (OW) is rapidly appearing as a winning waste management strategy by producing energy and anaerobic digestates that can be used as fertilizers in agricultural soils. In this context, the management of the OW treatment process to maximize agro-system sustainability satisfying the crop nutrient demands represents the main goal. To investigate these traits, two protocols to assess the plant availability of digestate nitrogen (N) and phosphorus (P) were evaluated. With this aim, the N and P availability was determined on 8 digestates and 2 types of digestate-based compost from different OW via sequential chemical extractions (SCE). In addition, the digestates were tested in soil incubations and in plant pot tests with Italian ryegrass and compared with chemical fertilizer and a non-amended control soil. The N extracted from digestates via SCE was related to soil N mineralization and plant N recovery. The C: N ratio had negative impact on mineralized N and its recovery in shoots (ShootsN = −0.0085.(C/N)+0.172, r2 = 0.67), whereas water extractable mineral N was positevely related to the root N apparent recovery fraction (N-ARF) with (RootsN = 5E−5.Nsolublemin+0.0138, r2 = 0.53). The shoot P-ARF was positively correlated with the inorganic water extractable fraction of P (ShootsP =0.1153.H2O-Pi−0.2777.H2O-Po+0.0249, r2 = 0.71) whereas the root P-ARF was positively correlated with the less accessible fractions (RootsP = (b) 0.0955.NaHCO3-Po+0.0955.NaOH-Po-0.0584NaHCO3-Pi+0.0128, r2 = 0.8641). Feedstock digestate typology impacted the N and P recovery results leading to a better description of the typology properties and a first nutrients ARF prediction.