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Using livestock residues as alternative fertilizers is a sustainable practice which recycles nutrients that would otherwise be lost. However, organic fertilizers may have a large impact on N2O emissions, offsetting the beneficial effects of C sequestration. After four years from biochar application, greenhouse gas fluxes were monitored for two years from a Maize field fertilized with digestate, slurry, or urea, with and without biochar. The objectives of the present study were to assess (i) the climate feedback of using residues from the livestock chain as alternative fertilizers and (ii) the contribution of biochar in mitigating GHGs emissions, while increasing the organic C in soil. Digestate was shown to have the highest impact on CO2 and N2O emissions from soil, with respect to mineral fertilization (+29 and +142%), more than slurry (+21 and −5%), whereas both residues positively affected CH4 uptake (+5 and +14%, respectively). The maximum N2O peaks occurred between 7–20 days after fertilization, accounting for 61% of total emissions, on average. Biochar was effective in reducing N2O emissions derived from mineral fertilization and digestate (−54% and −17%, respectively). An excess of labile organic matter and N induced the highest CO2 emissions and N2O peaks, independent of—or even triggered by—biochar. Mitigation of GHG emissions, from soils fertilized with livestock chain residue, can be obtained using biochar, but with limitations dependent on (i) the quantity of organic matter added, (ii) its quality, and (iii) the time from application: those aspects that deserve further investigations. [ABSTRACT FROM AUTHOR]

Biochar, included as a soil amendment by EU Regulation 2019/1009, has been shown to increase soil organic C stock and nutrient retention. We investigated the effect of biochar incorporation alone (B) and in association with mineral (BMin), digestate (BDig) and slurry (BSlu) fertilization, compared to the respective controls without biochar (C, Min, Dig and Slu), in a silage maize–Italian ryegrass rotation, on yield, soil fertility parameters and nitrous oxide (N2O) emissions. Two types of biochar in three doses (0.2, 0.45, 0.9%) were tested in two cropping seasons. Biochar did not significantly affect maize yield; however, BDig tended to increase silage yield and the ear component compared to Dig, while BMin tended to reduce maize N uptake compared to Min. Biochar incorporation significantly increased soil organic C (+31%) and cation exchange capacity (CEC) (+13%) in all the fertilization treatments; BMin and BDig also showed an increase compared to biochar alone (B). Emission of N2O was mainly driven by fertilization, digestate exhibiting the highest emissions. Biochar addition decreased the cumulative N2O emissions consistently in all the fertilization treatments, though not significantly. The association of biochar with organic fertilizers, in particular digestate, appears promising in increasing the fertilizer efficiency and reducing N2O emissions. [ABSTRACT FROM AUTHOR]