Research focusing on the nitrogen (N) application and N use of forage maize (Zea mays L.) in the boreal region is either limited or non-existent. The aim of this study was to investigate the response of yield, quality and N recovery efficiency (N_RE) of forage maize to an increase in the N application rate and different climatic conditions in two locations in Finland. The field experiment was conducted in southern (Helsinki; 60° N) and central (Maaninka; 63° N) Finland in 2019 and 2020. Dry matter (DM) yield, forage quality and N_RE were determined for N application rates of 100, 150 and 200 N kg ha⁻¹. The DM yield was similar to all studied N application rates. Moreover, there were no marked differences in the studied forage quality traits or the N_RE following the N application rates. However, the N_RE of maize was generally low at 45%. The current study recommends a N application rate of 100–150 N kg ha⁻¹ for forage maize in the boreal region. There is no need to increase the N application from current recommendations since climate conditions seem to limit the growth, development and N_RE of forage maize. The observed low N_RE of forage maize warrants further research in the future.

Forage maize (Zea mays L.) yield and nutritional quality fluctuate markedly in Northern Europe due to weather conditions. A field experiment was conducted in Southern Finland (Helsinki, 2018–2020) and in Central Finland (Maaninka, Kuopio, 2019–2020) to study the effect of harvest time and use of mulch film, in order to optimize the dry matter (DM) yield and quality. Treatments included oxo-biodegradable mulch film and no mulch, and three harvest times (the latter only in Helsinki). Mulch film increased DM yield on average by 2.3 Mg ha^-1 in Helsinki and by 3.8 Mg ha^-1 in Maaninka. Mulch film had a minor effect on the quality, and overall, the quality improved, although DM yield accumulation had already ceased. Nevertheless, the starch contents fluctuated and remained mostly below the target rate – 300 g kg^-1 DM – especially in Central Finland. The results indicate that mulch film improves forage maize yield, but a late harvest is still required to improve forage quality. However, climate conditions still restrict starch accumulation to ears in Northern European climate conditions, especially in the important milk production area in Central Finland.

Purpose: The land use and land use change (LULUC) emissions and removals are an important part of the carbon footprinting of forest products with the life cycle assessment (LCA). For example, in Finland, forests are an important—though reducing—carbon sink, which is not typically visible in global warming potential (GWP) of forest products. To improve the accuracy of forest LCA, a province-level dataset was combined for specific Finnish provinces following a top-down approach. Methods: The dataset of GWP_LULUC was created from Finnish forest statistics data from 2015 to 2021. A total of eight provinces from the northern and eastern Finland were included. The carbon pools in the dataset included living biomass (trees), mineral soils and drained organic soils. As a case study, the dataset values were applied for m³ and tonne C of harvested wood biomass of Norwegian Spruce, as well as 1 l of bioethanol production and 1 l of E20 (20% blend of bioethanol with petrol) vehicle use. Results and discussion: GWP_LULUC values varied between the studied provinces, from net negative to net positive. The variation was mostly attributed to living biomass carbon stock, followed by areas of drained organic soils in different provinces. Overall, GWP_LULUC showed an increasing trend in 2015–2021. When GWP_LULUC was added to the GWP of harvested wood biomass, it dominated and led to net negative GWPs in half the studied provinces. Yet, if GWP_LULUC emissions continue increasing, the currently net negative GWPs may approach zero and even become net positive. The contribution of GWP_LULUC was also high for bioethanol production and varied between the studied provinces. Conclusions: The created dataset will help improving the accuracy of Finnish forest LCA assessments and will be especially important for comparisons between fossil and bio-based products. The findings of the case studies highlight the importance of using province-level data in forest LCA whenever they are not limited by traceability and data availability.

Purpose: Recently, carbon opportunity cost (COC) approach has been mentioned in the European Commission’s draft of the updates on the Product Environmental Footprint (PEF) method, yet the COC approach has several limitations. In this commentary article, we aim to highlight the methodological and practical challenges of using COC approach in product environmental footprinting with life cycle assessment (LCA). Methods: The COC approach is typically based on the “foregone carbon sequestration” due to continued land use which postpones the natural regeneration. The foregone sequestration typically equals the difference in carbon stocks between current land use and the potential natural vegetation. In principle, the global warming potential (GWP) related to the transformation from historical land use (natural vegetation) to current land use overlaps with the GWP of the foregone sequestration. As an alternative to avoid double counting, we describe an additional COC approach. Results: The COC approach includes a risk of double counting, if it is applied simultaneously with the land transformation approach in product environmental footprinting with LCA. Double counting leads to overestimation of anthropogenic environmental impacts and harms the LCA principle of additivity. Furthermore, the suitability of the COC approach in attributional LCA is limited, since it does not represent the anthropogenic environmental impacts compared with the non-anthropogenic natural baseline. Regardless of the benefits of the additional COC approach in terms of avoided double counting, any COC approach includes high uncertainties related to the estimation of historical carbon stock and potential natural vegetation carbon stocks. Furthermore, the additional COC approach only provides benefits if potential natural vegetation exceeds the historical carbon stock. Conclusions: Overall, the COC approach based on foregone sequestration has a risk of double counting. Furthermore, any COC approach has high uncertainties and limited practical benefits, and therefore, we highly recommend keeping COC approaches apart from the European Commission’s PEF method.