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

Vetch-oat mixture — BMP: 2 studies, weighted mean 405 m³ CH₄/t VS

A vetch and oat mixture is a classic green forage or cover crop, combining a legume with a grass cereal. The dataset is based on a small number of records from a single Finnish study.

CH₄ ≈ 52 % (estimate)

Published 10 December 2021Updated 29 October 20263 min readFeedstockData Editorial Team

Photo Krzysztof Ziarnek, Kenraiz / Wikimedia Commons, licence CC BY-SA 4.0, source file; changes: cropping

Weighted mean: 405m³ CH₄/t VS
Range: 400–410m³ 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 (405); 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	400	35 °C · mesophilic	Vetch oat mixture 50% common vetch 50% oat	end point (model curve)
Lehtomaki (2006) · 2	410	35 °C · mesophilic	Vetch oat mixture 50% common vetch 50% oat	end point (model curve)
Weighted mean	405	arithmetic mean 405, SD 7

Typical composition

Dry matter (DM): 20.6% (range 15.5–25.6)
Nitrogen: 2.9 % DM
C/N ratio: 16

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
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 405 m³ CH₄/t VS (median 405; range 400–410; 2 records from 1 sources).

Drawbacks and risks

Spread of results in the database: standard deviation 7 at a mean of 405 m³ CH₄/t VS (2 records from 1 sources).

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

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

The vetch and oat mixture is a traditional fodder mixture: vetch, a leguminous plant with climbing shoots, uses oats as a support. It is grown for green forage, silage or as a catch crop. The dataset contains several records from a single Finnish study for a mixture in a proportion of half common vetch and half oats, examined under mesophilic conditions.

Properties relevant to digestion

Vetch contributes protein and nitrogen, and oats carbohydrates and fibre, so the mixture has a more balanced C to N ratio than oats alone. Digestibility depends on the stage of development: it is best before the oat heads emerge and the vetch seeds form, after which the share of woody stems increases. Ensiling is possible, but the protein content increases buffering capacity, so wilting is recommended. The material is seasonal, and its yield and composition vary between years. At a large share of the mixture in the feed, the risk of ammonia release increases.

How to read the spread of results

The records come from a single study and have the same description of the mixture, so the divergence between them reflects the variability of replicates or dates, not different materials. In reality the result depends on the ratio of vetch to oats in the crop (which changes from year to year), the harvest date, the form of the material and sample preparation. Test parameters are added to this: inoculum, substrate-to-inoculum ratio and test length. Given the limited database, the results are indicative.

In biogas plant practice

The vetch and oat mixture is suitable as a supplement on farms that grow it for feed or as a cover crop. It should be harvested at the appropriate stage, shredded and ensiled in line with good practice. In the mix it works well with nitrogen-poor substrates. Harvesting a cover crop involves costs and weather risk, so planning of supplies should take yield variability into account. The dose is worth verifying with a BMP test. Because the botanical composition of the crop changes from year to year, the result from one batch should not be carried over to subsequent seasons without checking. A simple analysis of the share of vetch in a sample of green forage and comparison with previous deliveries is sufficient.

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.