Abstract
The carbon (C) and nitrogen (N) mineralisation rates of five digestates were studied and compared with pig slurry, compost, and a solid fraction of digestate in aerobic incubation experiments. The objective was to identify the most relevant drivers of C and N mineralisation based on the physicochemical properties of the products. Net organic nitrogen mineralisation of digestates (Nmin,net) was on average 30%, although the range was relatively wide, with digestate from pig manure (39%) reaching double the value of digestate from sewage sludge (21%). The total carbon to total nitrogen (TC:TN) (r = −0.83, p < 0.05) and ammonium nitrogen to total nitrogen (NH4+-N:TN) (r = 0.83, p < 0.05) ratios of the products were strongly correlated with Nmin,net, adequately mirroring the expected fertilising potential of the products. The digestates had C sequestration values between 50 and 81% of applied total organic carbon (TOC), showcasing their potential to contribute to C build-up in agricultural soils. The carbon use efficiency of the amended soils was negatively correlated with dissolved organic carbon (DOC) (r = −0.75, p < 0.05) suggesting that catabolic activities were promoted proportionately to the DOC present in these products. Ratios of DOC:TOC (r = −0.88, p < 0.01) and TC:TN (r = 0.92, p < 0.01) were reliable predictors of the fraction of C that would remain one year after its incorporation and thus could be used as simple quality parameters to denote the C sequestration potential of digestates prior to their use in the field.
Highlights
The European Union (EU) has resolutely set its sights on transitioning away from the linear paradigm of “take, make, dispose” towards a circular economy model that fosters the reducing, reusing, and recycling of resources, as exemplified by the adoption of the Fertilising Products Regulation (FPR) ((EU) 2019/1009), which sets the stage for a unified European market of organic waste-derived fertilisers
For undigested pig slurry (U_PS), total carbon (TC) was in the lower range (277 g TC kg−1 DM) while its TC:Total nitrogen (TN) ratio was the lowest of all at 1.99
total organic carbon (TOC):TC was relatively widespread across products (0.77–0.99), the highest value coming from COM_1, the lowest from U_PS (Table 4)
Summary
The European Union (EU) has resolutely set its sights on transitioning away from the linear paradigm of “take, make, dispose” towards a circular economy model that fosters the reducing, reusing, and recycling of resources, as exemplified by the adoption of the Fertilising Products Regulation (FPR) ((EU) 2019/1009), which sets the stage for a unified European market of organic waste-derived fertilisers. This vision will involve the upscaling and incentivisation of C farming initiatives, understood as a series of practices intended to increase C removal and storage in the land sector This roadmap should translate into concrete actions such as the enhancement and conservation of soil organic carbon (SOC) in arable land. Biomethane is rapidly gaining traction for its potential to decarbonise both the transportation sector and the public gas grid [3,4] It follows that with an increasing capacity to process organic waste streams owing to the European AD sector’s steady growth, the opportunity arises to develop adequate management strategies for digestate [5]. With this new hybrid class of fertilisers, among which digestate is featured, the current maximum nitrogen (N) application limit of 170 kg N ha−1 y−1 etched in the Nitrates Directive (ND) (91/676/EEC) would be lifted for certain animal manure-derived products in Nitrate Vulnerable Zones (NVZ)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
