Swap straw is a new way to circulate straw

Straw swaps can optimise the yield of straw as a resource, so the straw is first used as bedding and then for biogas.

By Sofie Thanning Bell and Thomas Vang Jørgensen, ØkologiRådgivning Danmark

Disclaimer: This article has been automatically translated for your convenience. Reasonable efforts have been made to provide an accurate translation, however, errors or inaccuracies may occur, and some content (such as images, videos, PDF-files, etc.) has not been translated.

Straw has become a coveted commodity with competitive demand. This pushes up the price for heating plants, biogas, fertiliser and bedding. Sometimes, however, it may be possible to fulfil several of the straw's purposes.

When straw is burned in a heating plant, it obviously cannot be used again. If it is instead used as deep litter, it has actually been enriched for use in a biogas plant, and it still has nutritional value in the field when the digestate is returned from the biogas plant. This article illustrates the possibilities of combining all three utilisation options and how each party in the collaboration can make a profit from the straw.

Scenarios for the utilisation of straw

The BiogasDanmark trade association is working on scenarios for utilising animal manure, straw, catch crops and other biomasses from agriculture in biogas plants. Depending on which scenario is realised, the ambition is for biogas to replace Denmark's natural gas consumption by 2030 or 2033 at the latest.

Figure 1. Source: Biogas Outlook 2024 Biogas Denmark

Price is a barrier to using more straw for biogas

The main reason why biogas plants do not use more straw today is that straw is a relatively expensive raw material because it is alternatively used in straw heating plants. This means that farmers use as little straw as possible. As for biogas plants, on top of the high price of the raw material, they can add a large expense to pre-treat the straw to produce gas from it.

In short, the price of straw to heating plants is a barrier to using more straw in biogas plants. Although there are sufficient quantities of straw and crop residues available nationwide, it is inevitable that there will be a local battle for straw between livestock producers and biogas plants, unless we can succeed in creating co-operation between livestock producers, crop growers and biogas plants for the biomass that is available.

Sensible pricing of straw

The current prices for deep litter at around DKK 40/tonne do not incentivise livestock producers to deliver more deep litter for biogas, and biogas plants have no incentive to buy dry straw.

A market price for straw of around DKK 700-800/tonne and a settlement price for deep litter for biogas of DKK 0-40/tonne means that there is a lot of financial leeway to find a price point that allows biogas plants, livestock producers and crop growers to get a reasonable settlement for straw. At the same time, all parties earn more money because the straw that is currently cut in the fields is used for bedding, goes to biogas plants as deep bedding, and ends up at the straw producer as degassed biomass.

Straw exchange: more straw for bedding and biogas

A beneficial collaboration could be for biogas plants to buy straw directly from crop growers and lend it to livestock producers. The livestock producers use the straw for bedding and deliver it to the biogas plant as deep litter and slurry, and the biogas plant delivers the degassed biomass back to the crop farmer who produced the straw. The model is outlined below.

The collaboration is based on the biogas plant buying straw from the crop farmer at a price lower than the market price in return for the crop farmer receiving nutrients as degassed biomass. The biogas plant lends the straw to livestock producers who use it for bedding and send it to the biogas plant in slurry or as deep bedding.

Figure 2: The principle of co-operation between farmers and biogas producers illustrated. Ecological Consultancy Denmark.

Swapping straw has benefits for all parties

For the livestock producer:

Always straw available
No or reduced costs for purchased straw

For the crop grower:

Sells straw that would otherwise be cut
Structural value and fertiliser value from straw is returned
Saved cost of chopping

For the biogas plant

Increased amount of straw as raw material
More spreading area for degassed biomass at crop growers
Saved costs for pre-treatment of straw

What is an acceptable straw price?

The price of straw depends on the options available to sell it. Farmers have different ideas of what an acceptable straw price is, and the list below is a suggestion of what an acceptable straw price could be for farmers. The values are calculated based on budget calculations from Farmtal-Online 2025.

Farmer A: Straw is sold to a heating plant or mushroom production. Straw price DKK 720/tonne.

Farmer B: Straw is sold to a biogas plant, which returns the degassed biomass. Market price DKK 720/tonne minus structural value DKK 150/tonne minus fertiliser value DKK 70/tonne = DKK 500/tonne.

Farmer C: The farmer is happy as long as he can get rid of the straw at no cost. Recovers costs for salvage and storage. Baling, shredding, haulage and storage DKK 370/tonne.

Farmer D: The farmer usually chops the straw after the combine harvester and wants to keep the straw nutrients on the farm. In the swap straw model, he covers the costs of salvage and storage and saves on cutting costs for the combine harvester. 355 DKK/tonne. Baling, shredding, haulage and storage 370 DKK/tonne minus cutting costs 15 DKK/tonne.

The biogas plant can produce biogas on loan straw for deep litter when the straw price is DKK 370/tonne or lower, i.e. farmer scenario C and D with the same costs or lower than if they use pure dry straw.

Swap straw: what does the livestock producer have to pay?

If the biogas plant needs to maintain low production costs during periods with low gas prices, e.g. DKK 1._48/m3CH4, the livestock producer needs to pay for the straw. The calculation example below shows what the livestock producer needs to pay for straw if the biogas plant's costs are to be maintained at the level for deep litter as in scenario D above.

	Crop grower	Livestock producer		Biogas plant
	Sales price⁽¹⁾	Net, purchase cost	Selling price⁽¹⁾	Production cost
	Straw, kr./t.	Straw, kr./t.	Deep litter, kr./t.	Kr._/m3CH4
D. Loan straw	+355	-235	+40	1,48

1)Including biogas costs for storage and return to the farmer

The loan straw model has the potential to significantly reduce the price of straw for biogas. At the same time, it lowers the price of straw for bedding, and a larger part of the available straw passes through the stables before it reaches the biogas plant. This saves the biogas plant costs for pre-treatment of straw.