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BMP testingGrasses, green forage and fodder plantssingle study (4 samples)

Ryegrass — BMP: 4 studies, weighted mean 520 m³ CH₄/t VS

Ryegrass is a high-yielding forage grass, grown as green forage and silage. In the compilation it is described by a single study covering several growth stages.

rating: goodCH₄ 61 %

Published Updated 3 min readFeedstockData Editorial Team

Photo Stephen James McWilliam / Wikimedia Commons, licence CC0 1.0, source file; changes: cropping

Weighted mean
520m³ CH₄/t VS
Range
409–627m³ CH₄/t VS
Records
4single study (4 samples)
Publications
1source
Temperatures
40 °Cof the test

Methane in biogas

High methane content · ≈ 6.1 kWh/m³ of biogas

measured mean of 4 studies BMP, range 58–62.8 %; in a batch test the CH₄ share tends to be higher than in a plant.

How we calculate it and what the zones mean

Rating for biogas plants

good — editorial rating for biogas plantsStable, usually accepted without a fee

Potential per tonne of fresh matter: very high (102 m³ CH₄/t); process risk: acidification. Handling costs: fibres, floating layer.

Why? Rating factors

Potential per tonne +3

  • +3potential 102 m³ CH₄/t fresh matter (BMP 520 × DM 21.6 % × VS 90.9 %)

Process stability −0.5

  • −0.5acidification: rapid degradation / acidic pH, risk of VFA accumulation, needs buffering

Handling and costs −0.5

  • −0.5fibres, floating layer — shredding and intensive mixing

Total points: 2 · thresholds: ≥ 2.5 very good, ≥ 1 good, below — neutral; negative with cumulative process risk.

Editorial rating per the methodology · confidence of the rating: low · excluding market prices

Add to the co-digestion calculator CSV data

BMP curves from 4 studies

Weighted mean Individual records

BMP curves: RyegrassCumulative methane production over time for 4 records and the weighted mean of 520 m³ CH₄/t VS. 4 of the curves are model curves (first-order kinetics).02004006008000510152025303540time [d]m³ CH₄/t VSPouech (b.r.) · 1: 409 m³ CH₄/t VS (model curve)Pouech (b.r.) · 2: 423 m³ CH₄/t VS (model curve)Pouech (b.r.) · 3: 619 m³ CH₄/t VS (model curve)Pouech (b.r.) · 4: 627 m³ CH₄/t VS (model curve)mean520

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 (520); 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
SourceBMP
m³ CH₄/t VS		CH₄ in biogas
% vol., measured		TemperatureSampleCurve
Pouech (b.r.) · 140960.1 %40 °C · mesophilicRay Grass Silageend point (model curve)
Pouech (b.r.) · 242362.8 %40 °C · mesophilicRay Grassend point (model curve)
Pouech (b.r.) · 361962.6 %40 °C · mesophilicRay Grassend point (model curve)
Pouech (b.r.) · 462758.0 %40 °C · mesophilicRay Grassend point (model curve)
Weighted mean52060.9 %arithmetic mean 520, SD 120

Typical composition

Dry matter (DM)
21.6% (range 21.6–21.6)
Volatile solids (VS)
90.9 % DM (range 90.9–90.9)
Nitrogen
2 % DM

Median and range of the determinations reported in the publications behind this substrate's BMP records (read from: CROPGEN D4); dry matter: 1 determination, volatile solids: 1 determination. DM from a single determination – indicative value.

Sources: Pouech, P. Fruteau, H. Bewa, H.. Agricultural crops for….

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

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.

No published process studies

The literature we use does not describe the advantages or drawbacks of digesting this substrate beyond the BMP test results. Below are process characteristics assigned on the basis of the type of material — an editorial classification, not a study result.

seasonal
seasonal availability — requires storage
fibrous
lignocellulose, long fibres → floating layer, harder mixing, slow degradation
easily degradable
sugars, starch, glycerol → fast hydrolysis and acidification (VFA), needs buffering

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

Dosing

No source-based dose limits; like other grasses — mixing with excrement.

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

  1. Pouech, P. Fruteau, H. Bewa, H. (None) Agricultural crops for biogas production on anaerobic digestion plants. Biomass for energy and industry 163-165
  2. Weiland, P. (2010) Biogas production: current state and perspectives. Applied Microbiology and Biotechnology
  3. Hendriks, A.T.W.M.; Zeeman, G. (2009) Pretreatments to enhance the digestibility of lignocellulosic biomass. Bioresource Technology
  4. Herrmann, C. et al. (2011) Effects of ensiling, silage additives and storage period on methane formation of biogas crops. Bioresource Technology

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

What it is and where it comes from

Ryegrass (genus Lolium) is a grass of high forage value, grown on sown meadows, in mixtures and as an alternating crop on dairy farms. It gives several cuts a season. The compilation contains several records from a single study: silage and ryegrass samples at different growth stages, all under mesophilic conditions. The records have no year assigned in the source database.

Properties relevant to digestion

Ryegrass contains a relatively large amount of soluble sugars, which eases ensiling and allows a stable, well-keeping silage to be obtained. Digestibility declines with maturation: at the heading stage the share of fibre and lignin is greater than in young green forage. The material works well with slurry and other substrates, because it has a moderate C/N ratio and carries no significant inhibition risks. A problem is sometimes contamination with soil and, at times, the formation of a floating crust when the fibre is long, which requires shredding.

How to read the spread of results

The records come from a single publication, and their variation mainly reflects the growth stage and the form of the material (silage and green forage). In practice the result is affected by the variety (tetraploid or diploid), cut number, nitrogen fertilisation, mowing date, ensiling method and particle size. Test parameters are added: inoculum, substrate-to-inoculum ratio and test length. A single source does not give a full picture of year-to-year and regional variability.

In biogas plant practice

Ryegrass can be a valuable component of the mix on farms that grow it, especially in the form of silage from lower-quality cuts or surpluses. It is harvested at an early stage to obtain better digestibility, and ensiled in accordance with good practice. The dose can be substantial, because the material is relatively safe for the process, but care must be taken over mixing. The energy value is worth confirming with a BMP test, taking the cutting date into account. If a biogas plant buys ryegrass from several farms, it is advantageous to record the cut number and harvest date for each batch. This later makes it possible to link changes in biogas production with silage quality and to plan mowing dates in subsequent seasons.

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

  1. Pouech, P. Fruteau, H. Bewa, H.. Agricultural crops for biogas production on anaerobic digestion plants. Biomass for energy and industry 163-165.

All sources of the site: bibliography.

Other substrates in the group “Grasses, green forage and fodder plants”