Protein yield and extractability of flood-tolerant perennial grasses cultivated on a riparian fen, affected by harvest and fertilisation frequency

Paludiculture, defined as agriculture on wet or rewetted peatlands has been proposed as a mitigation strategy to reverse unsustainable environmental impacts such as land subsidence, nutrient release to surface water and greenhouse gas emissions from traditional agriculture on drained peatland. In particular, the production of biomass feedstock from flood-tolerant perennial grasses for green biorefining to protein and other value-added products may be a viable economic and environmentally sustainable option for temperate peatlands. However, optimal quality characteristics of the biomass for protein extraction have yet to be defined.

In 2018, field plots cultivated with different flood-tolerant perennial grasses were established in an agricultural fen peatland in Denmark. Of these, a total of eight plots cultivated with reed canary grass (RCG) and tall fescue were each subdivided into six sub-plots with different management regarding harvest and fertilisation. Harvest frequencies ranged from one to five times in the period between mid-May to mid-October at intervals of 4-6 weeks. The sub-plots received fertilisation of 100 kg ha^-1 of both N and K prior to each harvest. Protein extractability of the grasses was assessed by lab-scale biorefinery techniques using a screw press followed by precipitation of true protein in the resulting juice. This was compared with protein fractions classified by the Cornell Net Carbohydrate and Protein System (CNCPS).  The biorefinery extractable protein yields (fresh weight) ranged from 10 % to 25 % of the fresh mass input, dependent on treatment, with summer harvests having the lowest yield. Evaluation of the easily extractable crude protein (CP) CNCPS fractions B1 and B2 showed yields of between 61.8 – 110.7 g CP kg^-1 DM.  Preliminary processing of data showed that the cumulative yields of extractable crude protein for the growing season seem highly affected by management.