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Lime (CaCO3) application has led to an inconsistent mitigation of greenhouse gas emissions (GHGs) from agricultural soils. In addition, only a few studies have investigated the impact of gypsum (CaSO4) on the release of GHGs. Therefore, here we investigated the impact of initial soil pH and nitrogen sources on CaSO4 and CaCO3 effectiveness in reducing the production of GHGs. We hypothesized that (i) liming presents the highest effectiveness in reducing GHGs when performed in acidic soil and under NO3−‐N fertilizer application, and (ii) application of CaSO4 is not effective in reducing GHG irrespective of the initial soil pH or nitrogen (N) source. Firstly, an incubation experiment was carried out to evaluate the effect of initial soil pH using acidic soil and neutral soil amended with CaSO4 and CaCO3. Subsequently, a second incubation experiment was conducted to investigate the effect of N source by applying calcium nitrate and urea in an acidic soil amended with CaSO4, CaCO3 and CaSO4 + CaCO3. The measured variables were soil pHH2O$$ {\mathrm{pH}}_{{\mathrm{H}}_2\mathrm{O}} $$, daily and cumulative emissions of N2O‐N, CO2‐C and CH4‐C, as well as NH4+‐N and NO3−‐N concentrations. CaCO3 did not affect N2O‐N emission under neutral soil pH, and NO3−‐N fertilizer application. However, CaCO3 increased N2O‐N release under acidic soil (+96%), and urea fertilizer application (+97%). Furthermore, CaCO3 and CaSO4 reduced CO2‐C emission from the neutral pH soil by 31%, and CaSO4 decreased the mean cumulative N2O‐N release from the soil fertilized with urea‐N by 43%. In conclusion, this study did not confirm liming as an alternative to reduce N2O‐N release under different initial soil pH and N sources. Furthermore, our results indicated that CaSO4 may decrease GHG emissions. Finally, these results suggest caution for considering liming as a strategy to mitigate N2O‐N emission from agriculture. [ABSTRACT FROM AUTHOR]

The acidic soils of western Newfoundland require liming for successful production of most crops. Locally sourced paper mill waste wood ash (WA) and paper sludge (SL) have potential as cheaper alternatives to limestone (LIME). Two greenhouse experiments evaluated WA and SL as liming and soil conditioning amendments for annual ryegrass (Lolium multiflorum) production. At 55 days after seeding, soil pH in WA (6.2 and 6.3) and wood ash and paper sludge (WASL) (6.0 and 6.3) were not different from that in LIME (6.0 and 6.5) for Experiments 1 and 2, respectively. However, pH in SL was 0.4 and 0.3 points lower than in LIME. Compared to LIME, WA, SL, and WASL produced 31%–52% and 57%–74% greater biomass yield in Experiments 1 and 2, respectively. N uptake was greater in WA (60 and 129 kg N ha−1) and WASL (51 and 97 kg N ha−1) compared to LIME (40 and 85 kg N ha−1), in Experiments 1 and 2, respectively. SL did not differ from LIME in Experiment 1, but reduced N uptake by 57% in Experiment 2. The results show significant potential of WA as an alternative amendment for liming and yield improvement of annual ryegrass grown in NL podzolic soils. However, SL has limited potential due to the risk of increasing N immobilization and residual soil mineral N when growing conditions are limiting. Combining SL with WA or biochar seemed to alleviate these risks. Overall, the adoption of these amendments for field production systems warrants serious consideration, following supplemental field studies to determine optimal application rates and timing. Core Ideas: The podzolic soils of Newfoundland have low pH and fertility, hence require liming.Locally sourced wastes, such as paper mill wood ash (WA) and sludge (SL), could be used as liming and nutrient sources.WA was equivalent to limestone (LIME) in improving and sustaining optimal soil pH.WA produced 52% and 74% greater annual ryegrass yield than conventional LIME application in podzolic soils. [ABSTRACT FROM AUTHOR]