BMP testingGrasses, green forage and fodder plantssingle study (2 samples)

Marrow kale — BMP: 2 studies, weighted mean 315 m³ CH₄/t VS

Fodder kale (fodder cabbage) is a high-yielding brassica plant, considered as energy biomass. The compilation contains several records from a single Finnish study.

CH₄ ≈ 52 % (estimate)

Published 2 January 2024Updated 29 October 20263 min readFeedstockData Editorial Team

Illustration: FeedstockData (AI, Google Gemini)

Weighted mean: 315m³ CH₄/t VS
Range: 310–320m³ CH₄/t VS
Records: 2single study (2 samples)
Publications: 1source
Temperatures: 35 °Cof the test

Methane in biogas

≈51–54% CH₄

Medium methane content · ≈ 5.2 kWh/m³ of biogas

estimate from the substrate type The collected studies contain no measurement. The interval follows from the approximate composition (carbohydrate-dominated (no protein or fat characteristics)) and the yields of compound groups according to FNR.

How we calculate it and what the zones mean

Rating for biogas plants

not rated — editorial rating for biogas plants

Not rated: no dry matter or volatile solids in the data. We calculate the rating when the dry matter and volatile solids of the material are known.

Editorial rating per the methodology

Add to the co-digestion calculator CSV data

BMP curves from 2 studies

Weighted mean Individual records

Dashed lines are a model curve (first-order kinetics, B(t) = B₀·(1 − e^−kt)); the end point comes from the publication. All curves are model curves.

Cumulative methane production over the test [m³ CH₄/t VS]. The thick line is the weighted mean of all records (315); dots mark the end values given in the publications. Point at the chart to read values; click a legend item to hide or show a record.

Records and sources

Download CSV

Source	BMP m³ CH₄/t VS	Temperature	Sample	Curve
Lehtomaki (2006) · 1	310	35 °C · mesophilic	Marrow kale	end point (model curve)
Lehtomaki (2006) · 2	320	35 °C · mesophilic	Marrow kale	end point (model curve)
Weighted mean	315	arithmetic mean 315, SD 7

Typical composition

Dry matter (DM): 13.1% (range 13–13.1)
Nitrogen: 2.7 % DM
C/N ratio: 16.5

Median and range of the determinations reported in the publications behind this substrate's BMP records (read from: CROPGEN D4); dry matter: 2 determinations, volatile solids: 0 determinations.

Sources: Lehtomaki (2006).

The composition of the raw material varies between batches — for plant calculations use an analysis of your own sample. The calculator inserts typical values automatically.

Process properties

seasonal
dilutes the feed (low DM)
editorial classification

Low confidence: the description is based on general characteristics of the substrate group, not on studies of this material. Treat it as a hint to be verified.

Advantages

Methane potential in the database: weighted mean 315 m³ CH₄/t VS (median 315; range 310-320; 2 records from 1 source).

Drawbacks and risks

Spread of results in the database: standard deviation 7 at a mean of 315 m³ CH₄/t VS (2 records from 1 source).

Co-digestion — what to combine it with, what to watch out for

combines well
group: Animal excreta (slurry, manure, poultry litter)
Co-digestion with excreta (slurry/solid manure) is the standard arrangement for plant biomass: they supply alkalinity and microflora.^[1][2]

Dosing

No dose data; brassicas are sometimes a source of sulphur, but the sources cited here give no confirmation for this substrate.

Introduce gradually, starting with a small dose and monitoring the process (e.g. FOS/TAC, pH, gas composition).

Practical requirements

Ensiling makes it possible to store seasonal biomass; properly ensiled plants (in the study maize, sorghum, forage rye, triticale) can be stored for up to a year without loss of methane production (Herrmann et al. 2011).

Sources of the process data

Lehtomaki, A. Viinikainen, T.A. Rintala, J.A (2006) Screening boreal energy crops and crop residues for methane biofuel production. Submitted to Biomass and Bioenergy
Weiland, P. (2010) Biogas production: current state and perspectives. Applied Microbiology and Biotechnology
Herrmann et al. (2011). Effects of ensiling, silage additives and storage period on methane formation of biogas crops. Bioresour. Technol.

The co-digestion calculator will assess a specific mixture containing this substrate.

What it is and where it comes from

Fodder kale, also called fodder cabbage (Brassica oleracea var. acephala), is a plant grown as animal feed, particularly in cool climates. It produces a large mass of leaves and stems and tolerates lower temperatures, so it is sometimes harvested in late autumn. In the context of biogas it has been tested as a potential energy crop for northern Europe. The compilation is based on a small number of records from a single study, carried out under mesophilic conditions.

Properties relevant to digestion

Kale has a high moisture content and well-digestible biomass, with a share of readily available carbohydrates and protein, and at the same time stems with a higher fibre content. Brassicas contain sulphur compounds (glucosinolates), from which hydrogen sulphide can arise in the digester, lowering the quality of the biogas and having a corrosive effect on the installation. The high moisture content results in rapid degradation after harvest; the material should be ensiled or fed to the digester shortly after harvest. The protein content lowers the C/N ratio, but increases the risk of ammonia release at a large share in the ration.

How to read the spread of results

The records come from a single publication, so they do not give a full picture of variability. In real batches the result depends on the variety, the harvest date (after frosts the composition of the leaves changes), the share of leaves and stems, fertilisation, the form of the material (fresh or ensiled) and sample preparation. There are also test parameters: inoculum, S/I ratio and time. The data therefore do not include the variability that can be encountered in other climates and cropping systems.

In biogas plant practice

In Poland fodder kale is not a common energy crop and regular deliveries cannot easily be counted on. If a farm grows it for feed, surpluses can be ensiled and added to the mix in a limited share. Harvesting and ensiling require careful management, and in the biogas plant H₂S must be monitored and a working desulphurisation system must be in place. Because the data are based on a single study, your own BMP test is essential before wider use. If kale is to be grown specifically for the needs of a biogas plant, the demand for nitrogen and sulphur fertilisers must be taken into account, together with the costs of harvesting in late autumn, when weather conditions hinder the work of machinery and transport.

Methodology in brief

BMP is the amount of methane obtained from volatile solids (VS) in a batch test, given in m³ CH₄ per tonne of VS (numerically the same as NmL CH₄/g VS in the publications) and converted to normal conditions (0 °C, 101.325 kPa). The weighted mean gives each publication a total weight of 1, split equally between its results for the substrate — a paper testing twenty varieties does not outweigh a paper with a single sample. In inter-laboratory programmes the unit is the laboratory (total weight 1), and within it the weight of a test grows with the number of bottles (replicates). Results after pretreatment (e.g. thermal, chemical, enzymatic) are shown separately and are not included in the mean.

Solid lines are curves measured in the tests. Where a publication gives only the final result, we draw a first-order kinetic model, B(t) = B₀·(1 − e^−kt): only the end point comes from the publication, and the shape of the curve serves purely as visualisation — do not read the production on a particular day from it. For this substrate k = 0.091 d⁻¹ was assumed (no kinetic data for the group – the median of all available rate constants k (93 values) was used).

The statistics describe the spread of published results — a descriptive compilation, not a meta-analysis or a guarantee of plant yield.

Full methodology and correction policy

Bibliography

Lehtomaki, A. Viinikainen, T.A. Rintala, J.A (2006). Screening boreal energy crops and crop residues for methane biofuel production. Submitted to Biomass and Bioenergy.

All sources of the site: bibliography.