On-farm experimentation of anaerobic digestate distribution methods for advancing circular economy in the agroecosystem

Abstract Purpose This study evaluates the effectiveness of various anaerobic digestate distribution methods, including liquid digestate with a nitrification inhibitor, liquid digestate applied with variable rate application (VRA), and solid digestate, compared to mineral fertilizer. The objective was to assess their agronomic performance, nitrogen use efficiency (NUE), and environmental impact in winter wheat production within a circular economy framework. Method A two-year on-farm experiment was conducted across two farms covering a total area of 47 hectares. The treatments evaluated included liquid digestate with nitrification inhibitor (LD+), liquid digestate with variable rate application (VRA), liquid digestate with both nitrification inhibitor and VRA, solid digestate (SD) and mineral fertilizer (MF) with or without VRA. The study measured wheat yields, protein content, nitrogen use efficiency (NUE), and compared the agro-environmental sustainability of digestate and mineral fertilizer applications. Results Winter wheat production under digestate applications achieved yields (>5.9 t ha −1 ) and protein content (>5.3%) comparable to mineral fertilizer. The mineral fertilizer showed higher NUE (69%) than all digestate fractions, with LD+ at 43% and SD at 25%. The liquid digestate application with VRA increased NUE to 49%, but the nitrification inhibitor had no significant effect on NUE.The agronomic performance of solid digestate was comparable to mineral fertilizer at one site but lower at the other. However, solid digestate exhibited lower agro-environmental sustainability. Conclusion Liquid fractions of anaerobic digestate can serve as alternatives to mineral fertilizers, providing promising agronomic results when combined with precision farming techniques such as VRA. However, their NUE and overall performance were lower than mineral fertilizers, with variability across sites due to soil conditions and environmental factors. Solid digestate demonstrated mixed agronomic outcomes and raised concerns regarding its longer-term impact on soil sustainability. Further long-term studies are needed to assess its full effects on soil structure and organic matter dynamics.