Effects of Harvest and Fertilization Frequency on Protein Yield and Extractability From Flood-Tolerant Perennial Grasses Cultivated on a fen Peatland

Abstract

Paludiculture, and in particular the cultivation of perennial grasses as biomass feedstock for green biorefineries, may be an economic and environmentally sustainable option for agricultural peatlands in temperate regions. However, the optimal biomass quality for protein extraction from flood-tolerant grasses is largely unknown. The aim of this study was to define the combined effect of harvest and fertilization frequency, with one to five annual cuts, on protein yield and extractability for the grasses tall fescue (TF) and reed canary grass (RCG), cultivated on an agricultural fen peatland in Denmark.The content of protein fractions was determined according to the Cornell Net Carbohydrate and Protein System (CNCPS). We assessed protein extractability by lab-scale biorefinery techniques using a screw-press followed by acid precipitation of true protein. The two methods were compared to correlate potential extractable protein yields with actual biorefinery outputs. We found the highest annual biomass and crude protein (CP) yields in the two cut treatments, with 13.4 and 15.6 t dry matter (DM) ha−1 year−1, containing 2.9–3.4 t CP ha−1 year−1 for TF and RCG, respectively. The highest neutral-extractable (fractions B1 and B2) true protein yields of 1.1 and 1.5 t ha−1 year−1 were found in the two cut treatments, representing 39% (TF) - 45% (RCG) of total CP. Using biorefining techniques, we were able to precipitate up to 2.2 t DM ha−1 year−1 of protein concentrate, containing up to 39% CP. Significant correlations between methods were found, with a distinct relationship between CNCPS fractions B1 + B2 and CP yield of the protein concentrate, indicating the suitability of the CNCPS as an indicator for extractable protein yields. Biomass and CP yields were not significantly improved beyond two annual cuts. However, timing and harvest frequencies significantly affected plant maturity and consequently extractable CP contents and protein concentrate yields. We conclude that TF and RCG are promising feedstocks for green biorefineries due to high biomass, extractable CP, and protein concentrate yields, and highlight the potential of flood-tolerant grasses, cultivated on wet agricultural peatlands, for an enhanced valorisation beyond the common utilisation for bioenergy.

Coupling the benefits of grassland crops and green biorefining to produce protein, materials and services for the green transition

“…For biorefining, the protein content in grass biomass depends on nitrogen availability, frequency and timing of cutting, similar to the systems on intensive arable land. Recent research found crude protein contents of up to 2.9–3.4 t/ha/year, and precipitated protein concentrates of up to 1.2–2.2 t/ha/year, for reed canary grass and tall fescue, cultivated on wet organic soils (Nielsen, Stødkilde, et al, 2021). Optimal timing of harvest seems to remain the most critical factor for biomass and protein yields.…”

“…In addition to experiments on university experimental farms, research is also performed on farmers' fields; e.g. to analyse crop productivity and protein content, and greenhouse gas balance on lowland organic soils (Kandel et al, 2013, 2016; Nielsen, Elsgaard, et al, 2021, Nielsen, Stødkilde, et al, 2021).…”

“…The cultivation of flood-tolerant species, e.g. reed canary grass, festulolium and tall fescue on wet or temporarily flooded organic soils, also known as paludiculture, has documented high annual yields of up to 10-19 t DM/ha (Jørgensen et al, 2021;Kandel et al, 2013Kandel et al, , 2016Nielsen, Stødkilde, et al, 2021). This is comparable to the productivity of grass in rotation on drained soils under similar fertilisation rates of 160-240 kg N/ha per year.…”

Root-To-Shoot Ratios of Flood-Tolerant Perennial Grasses Depend on Harvest and Fertilization Management: Implications for Quantification of Soil Carbon Input

“…With an increasing policy focus on wetland restoration, including paludiculture, for GHG mitigation and nutrient retention, as well as the concomitant need to point out sites with the highest mitigation potential, not only assessments of GHG emissions and optimum management (e.g., Geurts et al, 2019;Tanneberger et al, 2020;Nielsen et al, 2021) but also siteand plant community-specific BGB NPP should be taken into consideration for an accurate evaluation of the C sink potential.…”

“…While currently an effort is made to review R/S for different biomes and climate zones (e.g., Qi et al, 2019), an assessment of the R/S of grasses under different harvest frequencies is still lacking. This is particularly true for flood-tolerant grass species, which are increasingly introduced on both wetland and upland soils for both climate change mitigation and added-value products, such as grass protein as a substitute for soy (Nielsen et al, 2021). Hence, there is a need for consolidated estimates of R/S for commonly used paludiculture crops under different harvest frequencies (Karki et al, 2014).…”