Comparison of GHG emissions from annual crops in rotation on drained temperate agricultural peatland with production of reed canary grass in paludiculture using an LCA approach.

Drained peat soils contribute significantly to global human-caused CO2 emissions and reducing peat degradation via rewetting is high on the political agenda. Ceasing agricultural activities on rewetted soils might lead to land owner resistance and high societal expenses to compensate farmers. Continued biomass production adapted for wet conditions on peat soils potentially minimizes these costs and helps supplying the growing demand for e.g. materials, fuels and feed. Here we used a life cycle assessment approach (cradle to farm gate) to investigate the greenhouse gas (GHG) emissions related to three cases by applying IPCC (Intergovernmental Panel on Climate Change) emission factors and specific site conditions at a bog and a fen site that represent widely distributed temperate peat soils. Besides soil emissions, upstream emissions from input, operational emissions and emission related to rewetting construction work were included. The analyzed systems were deeply drained cash cropping on agricultural bog (potatoes (Solanum tuberosum L.), spring barley (Hordeum vulgare L.) and oat (Avena sativa L.), permanent Reed canary grass (RCG) (Phalaris arundinacea L.) production on non-drained bog and permanent RCG production on shallow-drained fen. The annual mean water table depths (WTD) were -70, -38 (estimated) and -13 cm, respectively. Results showed estimated GHG emissions of 40.5, 26.1 and 20.6 Mg CO2eq ha-1, respectively, corresponding to a 35% GHG reduction for the non-drained bog case as compared to the drained bog case, despite that the obtained WTD due to ceased drainage did not adhere to the IPCC rewetting threshold of -30 cm. Emissions related to crop management represented 7, 14 and 19% of total emissions. In the RCG cultivation on fen case, the WTD were controlled primarily by the water table of the nearby stream and total GHG emissions were even lower as compared to the RCG production on the non-drained bog reflecting the difference in WTD. Rewetting projects need to include careful knowledge of the specific peat area to foresee the actual reduction potential.

Annual protein yield and extractable protein potentials in three legumes and two grasses.

BACKGROUND: New protein sources with low environmental and climatic impact are needed. Perennial crops show advantages as compared to annual crops and the upcoming biorefinery technology can extract proteins from the perennial biomass for protein concentrate production. The search for best-suited biomass crops needs to include harvest during the full growing season to support economic viability of biorefinery plants. Here we examined two grasses under increasing N fertilizer regime (175, 350 and 525 kg N ha-1 ) and three legumes, subject to a four-cut strategy. The well-defined Cornell Net Carbohydrate and Protein System (CNCPS) was used to estimate potential extractable protein. A key, previously presented in the literature, was applied in order to translate the CNCPS results into potential extracted protein concentrate. RESULTS: Crude protein (CP) yield per hectare was highest in red clover in 2015 (2907 kg CP ha-1 ) and the fertilized (525 kg N ha-1 ) tall fescue in 2016 (2435 kg CP ha-1 ). When translating the numbers into potential extraction of protein concentrate, the red clover had the highest protein concentrate yield per hectare in 2015 (835 kg CP ha-1 ) and lucerne in 2016 (803 kg CP ha-1 ). CONCLUSION: The results revealed that the entire season needs attention for optimization and not only the first cut, since both CP yields and quality peaks in different cuts across the five species and 2 years. Further knowledge of CP yield responses to field management and species mixtures are needed in order to advise farmers on the optimal crop for biorefining. © 2021 Society of Chemical Industry.

Linking Protein Quality in Biorefinery Output to Forage Crop Crude Protein Input via the Cornell Net Carbohydrate and Protein System.

The biorefinery technology aiming at protein extraction is rising and identification of suitable plant biomass input with valuable protein compounds for extraction is needed. Forage crops have been evaluated by the Cornell Net Carbohydrate and Protein System (CNCPS), and the result used as proxy of extractable protein in a biorefinery process. This serves as a helpful link between crop production and refinery output; however, the method has never been validated. Such validation is the main aim of this study. Five forage species-white clover, red clover, lucerne, perennial ryegrass, and tall fescue-were cut at four dates during spring and processed in a lab-scale refinery (screw press and subsequent protein precipitation from the green juice). The pulp fraction and the precipitated protein concentrate were both CNCPS analyzed to follow the initial crude protein (CP) plant input into these two fractions. Total recovery in concentrate was highest for the legumes, which points to an advantage of these species in protein extraction setups. High recovery of B1 and B2 (50% or higher for the grasses) in the pulp demonstrated a large proportion of soluble protein ending up in the fibrous pulp and shed light on the reason behind high feed quality of the pulp fraction. In conclusion, the existing tentative assumption of extractable protein being equal to CNCPS fractions of B1 and B2 and partly B3 was shown to be too simplified. The presented findings can improve crop species screening in terms of expected extractable protein yield.

Nitrous oxide emissions from oilseed rape cultivation were unaffected by flash pyrolysis biochar of different type, rate and field ageing.

Nitrous oxide (N2O) emission from winter oilseed rape (WOSR) cultivation may compromise the sustainability of oilseed rape biodiesel. Typically, greenhouse gas budgets of WOSR cultivation assume an N2O emission factor (EF) of 1% of the N added in fertilizer and crop residues. Management options to reduce direct soil emissions of N2O include the application of biochar, but efficacy and mechanisms of N2O suppression are elusive. We measured N2O emissions in a WOSR field trial on a sandy loam soil in Denmark over 402 days in 2017-2018, comparing biochar applications from two feedstocks (wheat straw and pig manure fibers), two application rates (1.5 and 15 Mg ha-1) and field ageing of up to three years. Further, a controlled incubation experiment was performed to examine the effect of biochar dose and ageing on N2O production and consumption by denitrification. Biochar treatments had no significant effects on cumulative N2O emissions (1.71-2.78 kg N ha-1 yr-1). Likewise, no significant effects were found on crop yield, yield-scaled N2O emission, soil mineral N content, gravimetric soil moisture or pH. The fertilizer induced EF was 0.51% which is well below the IPCC Tier 1 EF of 1%. High doses of fresh, but not field-aged biochar suppressed N2O production under anoxic conditions ex situ, suggesting that biochar with sufficient liming capacity could mitigate N2O emissions from denitrification also under field conditions. Yet, rates of up to 15 Mg ha-1 flash pyrolysis biochar in the current in situ study, which comprised a pronounced summer drought, showed no significant N2O mitigation. This highlights the need for selecting dedicated biochars and doses and test them in multi-year studies to conclude on their N2O mitigating effect. Yet, in relation to sustainability of WOSR cultivation for biodiesel, the current study suggests that C sequestration by biochar is not compromised by increased N2O emissions.

Biochar potentially mitigates greenhouse gas emissions from cultivation of oilseed rape for biodiesel.

Winter oilseed rape (WOSR) is the main crop for biodiesel in the EU, where legislation demands at least 50% savings in greenhouse gas (GHG) emissions as compared to fossil diesel. Thus industrial sectors search for optimized management systems to lower GHG emissions from oilseed rape cultivation. Recently, pyrolysis of biomass with subsequent soil amendment of biochar has shown potentials for GHG mitigation in terms of carbon (C) sequestration, avoidance of fossil based electricity, and mitigation of soil nitrous oxide (N2O) emissions. Here we analyzed three WOSR scenarios in terms of their global warming impact using a life cycle assessment approach. The first was a reference scenario with average Danish WOSR cultivation where straw residues were incorporated to the soil. The others were biochar scenarios in which the oilseed rape straw was pyrolysed to biochar at two process temperatures (400 and 800 °C) and returned to the field. The concept of avoided atmospheric CO2 load was applied for calculation of C sequestration factors for biochar, which resulted in larger mitigation effects than derived from calculations of just the remaining C in soil. In total, GHG emissions were reduced by 73 to 83% in the two biochar scenarios as compared to the reference scenario, mainly due to increased C sequestration. The climate benefits were higher for pyrolysis of oilseed rape straw at 800 than at 400 °C. The results demonstrated that biochar has a potential to improve the life cycle GHG emissions of oilseed rape biodiesel, and highlighted the importance of consolidated key assumptions, such as biochar stability in soil and the CO2 load of marginal grid electricity.

Using lidar to assess the development of structural diversity in forests undergoing passive rewilding in temperate Northern Europe.

Forested areas are increasing across Europe, driven by both reforestation programs and farmland abandonment. While tree planting remains the standard reforestation strategy, there is increased interest in spontaneous regeneration as a cost-effective method with equal or potentially greater benefits. Furthermore, expanding areas of already established forests are left for passive rewilding to promote biodiversity conservation. Effective and objective methods are needed for monitoring and analyzing the development of forest structure under these management scenarios, with airborne laser scanning (lidar: light detection and ranging) being a promising methodology. Here, we assess the structural characteristics and development of unmanaged forests and 28- to 78-year old spontaneously regenerated forests on former agricultural land, relative to managed forests of similar age in Denmark, using 25 lidar-derived metrics in 10- and 30-m grid cells. We analyzed the lidar-derived cell values in a principal component analysis (PCA) and interpreted the axes ecologically, in conjunction with pairwise tests of median and variance of PCA-values for each forest. Spontaneously regenerated forest in general had increased structural heterogeneity compared to planted and managed forests. Furthermore, structural heterogeneity kept increasing in spontaneously regenerated forest across the maximal 78-year timespan investigated. Natural disturbances showed strong impacts on vegetation structure, leading to both structural homogeneity and heterogeneity. The results illustrate the utility of passive rewilding for generating structurally heterogeneous forested nature areas, and the utility of lidar surveys for monitoring and interpreting structural development of such forests.