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BMP testingGrasses, green forage and fodder plantssingle study (5 samples)

Millet/foxtail millet and clover mixtures — BMP: 5 studies, weighted mean 304 m³ CH₄/t VS

Mixtures of millet or foxtail millet with clover are summer catch crops harvested as green forage. In the dataset they come from a single publication that describes several variants.

rating: goodCH₄ ≈ 53 % (estimate)

Published Updated 3 min readFeedstockData Editorial Team

Photo Tess Mattew / Wikimedia Commons, licence CC BY-SA 4.0, source file; changes: cropping

Weighted mean
304m³ CH₄/t VS
Range
276–374m³ CH₄/t VS
Records
5single study (5 samples)
Publications
1source
Temperatures
38 °Cof the test

Methane in biogas

Medium methane content · ≈ 5.3 kWh/m³ of biogas

estimate from the substrate type The collected studies contain no measurement. The interval follows from the approximate composition (protein from total nitrogen (N 1.5 % DM × 6.25)) and the yields of compound groups according to FNR.

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: high (77 m³ CH₄/t); no particular threats to stability. No additional handling requirements.

Why? Rating factors

Potential per tonne +2

  • +2potential 77 m³ CH₄/t fresh matter (BMP 304 × DM 28.4 % × VS 89 %)

Process stability 0

  • 0no factors

Handling and costs 0

  • 0no factors

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 5 studies

Weighted mean Individual records

BMP curves: Millet/foxtail millet and clover mixturesCumulative methane production over time for 5 records and the weighted mean of 304 m³ CH₄/t VS. 5 of the curves are model curves (first-order kinetics).01002003004000510152025303540time [d]m³ CH₄/t VSLallement et al. (2023) · 1: 276 m³ CH₄/t VS (model curve)Lallement et al. (2023) · 2: 282 m³ CH₄/t VS (model curve)Lallement et al. (2023) · 3: 285 m³ CH₄/t VS (model curve)Lallement et al. (2023) · 4: 304 m³ CH₄/t VS (model curve)Lallement et al. (2023) · 5: 374 m³ CH₄/t VS (model curve)mean304

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 (304); 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		TemperatureSampleCurve
Lallement et al. (2023) · 1 DOI27638 °C · mesophilicmillet and cloverend point (model curve)
Lallement et al. (2023) · 2 DOI28238 °C · mesophilicMix moha and cloverend point (model curve)
Lallement et al. (2023) · 3 DOI28538 °C · mesophilicmillet and cloverend point (model curve)
Lallement et al. (2023) · 4 DOI30438 °C · mesophilicmillet and cloverend point (model curve)
Lallement et al. (2023) · 5 DOI37438 °C · mesophilicmillet and cloverend point (model curve)
Weighted mean304arithmetic mean 304, SD 40

Typical composition

Dry matter (DM)
28.4% (range 15.9–50.3)
Volatile solids (VS)
89 % DM (range 88–92)
Nitrogen
1.5 % DM
C/N ratio
27.1

Median and range of the determinations reported in the publications behind this substrate's BMP records (read from: MY-D); dry matter: 4 determinations, volatile solids: 3 determinations. C/N was calculated as the ratio of C and N content (% DM) from the same source.

Sources: Lallement et al. (2023).

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
  • 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 304 m³ CH₄/t VS (median 285; range 276–374; 5 records from 1 sources).
  • A summer catch crop (millet or Moha with clover) described in the Lallement 2023 database.

Drawbacks and risks

  • Spread of results in the database: standard deviation 40 at a mean of 304 m³ CH₄/t VS (5 records from 1 sources).

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

Dosing

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

  1. Lallement, A.; Peyrelasse, C.; Lagnet, C.; Barakat, A.; Schraauwers, B.; Maunas, S.; Monlau, F. (2023) A Detailed Database of the Chemical Properties and Methane Potential of Biomasses Covering a Large Range of Common Agricultural Biogas Plant Feedstocks. Waste 1(1), 195–227
  2. Weiland, P. (2010) Biogas production: current state and perspectives. Applied Microbiology and Biotechnology
  3. 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

Millet and foxtail millet are warmth-loving cereals that grow quickly in summer, and clover is a leguminous plant that enriches the soil with nitrogen. Mixtures of these plants are grown as summer catch crops, that is, after the main crop is harvested, and are harvested as green forage or silage. The dataset includes several records from a single publication: several variants with millet and clover and one mixture of foxtail millet with clover, tested under mesophilic conditions.

Properties relevant to digestion

The composition depends on the proportions of the components: millet and foxtail millet supply fibre and carbohydrates, and clover supplies protein. The biomass is moist and relatively readily digestible if harvest takes place before ripening. Ensiling requires attention, because clover has a high buffering capacity and the sugar content may be low. The material is seasonal, and the catch crop yield is sometimes low and dependent on the weather in the second half of summer. At a large share of the mixture in the feed, the ammonia concentration may rise.

How to read the spread of results

Several records come from a single publication, so their variation reflects different variants of the mixture and batches, not independent sources. In reality the result depends on the proportions of the species, the sowing and harvest dates, the weather, the form of the material and sample preparation. The inoculum, the substrate-to-inoculum ratio and the test time also have an effect. The results therefore do not provide a reliable basis for planning production, but only give guidance on the range.

In biogas plant practice

Summer catch crops with millet or foxtail millet and clover can be an addition to the mix on farms looking for a way to increase biomass production without competing with food crops. The condition is good planning of sowing and harvest and the possibility of ensiling at suitable quality. They require shredding and checking that the material is not contaminated with soil. The dose range should be set after a BMP test of the farm's own batch. It is worth remembering that in dry years the yield of a summer catch crop may be very low, so a biogas plant should not base steady supplies on it. Treating it as an occasional supplement avoids feedstock shortages. It is also good to record the composition of the mixture and the harvest date of each batch.

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. Lallement, A.; Peyrelasse, C.; Lagnet, C.; Barakat, A.; Schraauwers, B.; Maunas, S.; Monlau, F. (2023). A Detailed Database of the Chemical Properties and Methane Potential of Biomasses Covering a Large Range of Common Agricultural Biogas Plant Feedstocks. Waste 1(1), 195–227. DOI: 10.3390/waste1010014 DOI

All sources of the site: bibliography.

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