Ramial Chipped Wood

Technical articles

Living soils Water management Weeding Nitrogen hunger Productivity Fertilization Agroforestry Soil regeneration NBSOIL RCW

Ramial Chipped Wood

Ramial Chipped Wood (RCW) corresponds to a mixture of shredded wood branch fragments. Its use, inspired by the functioning of forest soils, was developed in the 1970s in Canada. Spreading the shredding residues on agricultural soils promotes the development of soil fauna and flora, sources of many benefits for Water management, soil fertility, and crop productivity. RCW is considered an aggregating material whose primary purpose is to restore degraded soils and increase soil organic matter content. It is used both in large-scale crops and in market gardening or viticulture. Besides its interest for restoring agricultural soils, RCW can also serve as livestock bedding.

Wood decomposition and humus creation

Basidiomycete fungi in the soil are the microorganisms that initiate wood decomposition, particularly the lignin in wood. These soil fungi live in aerobic conditions (in the presence of air) and cannot survive at depth. Other insects and microorganisms constituting the soil fauna and flora then contribute to wood decomposition through the mechanical action of their mandibles and thanks to enzymes from lignivorous organisms. All this soil life is the origin of humus creation.

Composition of RCW

The table below provides an analysis of the composition of an RCW made from poplar branches.

Analyzed fraction nature	% in RCW composition
Cellulose	51%
Lignin	18%
Hemicellulose	14%
Soluble fraction	13%
Mineral matter	4%

Nutrient richness

Source CTA, B. Noel

Element	Mass per m³ of RCW
Nitrogen N	1.8 kg/m³
Phosphorus P2O5	1.8 kg/m³
Potassium K2O	1.7 kg/m³
Calcium CaO	7.0 kg/m³
Magnesium MgO	1.7 kg/m³

Benefits

A reasoned use of RCW provides many advantages :

Soil restoration

• Increase in soil organic matter and humus creation. The humus layer can reach a depth of 10 cm after 6 months and up to 20 to 30 cm after one year. Applying 100 m³ of RCW/ha allows obtaining 7.5 tons of humus/ha formed within two years after application. This corresponds approximately to the amount of humus that can be formed by 10 years of manure application.

• Improvement of soil structural stability, for which soil life is the main guarantor. By promoting the development of soil fauna and flora, RCW reduces compaction and soil erosion.

Water management

• In the short term, RCW reduces runoff and promotes soil moisture retention when used as mulch.

• In the longer term, it increases water infiltration and water storage in the soil through humus creation and enhanced soil biological activity. It increases crop resistance to drought and can reduce or even eliminate irrigation.

Crop productivity

• Yield increase, provided the phenomenon of nitrogen hunger is anticipated.
• Reduction of certain crop diseases such as fusariosis. Wood-decomposing organisms produce certain antibiotic molecules that protect crops from pathogens and parasites.
• Improvement of organoleptic qualities and shelf life of fruits and vegetables.
• Reduction or even elimination of weeds through a mulching effect.
• Reduction of young trees mortality.

RCW presents an economic interest if its use leads to increased yields and reduced use of chemical inputs.

It also helps limit water pollution caused by leaching of nitrogen from chemical fertilizers. Unlike nitrogen in nitrate form, nitrogen contained in humus cannot be leached because it is bound to organic matter (notably for protein formation).

Drawbacks

Using RCW comes with some drawbacks :

• RCW decomposition extends over several months.

• RCW can provide shelter for rodents (e.g., voles).
• Soil warming and drying are slowed in spring, which can delay crop establishment.
• Some crops such as root vegetables (carrots notably) may be hindered by the presence of RCW.
• A depressive effect on crops may be observed during the first 6 months after RCW application. Several factors can explain this effect : presence of allelopathic compounds, competition between soil flora, nitrogen hunger...
  

Allelopathy phenomena

Polyphenols, including tannins, and terpenes are allelochemical molecules produced by plants that can inhibit the germination and development of other plants or microorganisms. These molecules are natural antifungals. This type of interaction is similar to allelopathy, i.e., "all biochemical interactions between plants themselves or through microorganisms". These compounds can be responsible for a depressive effect on crops during the first six months after RCW use. They are produced in variable amounts depending on the tree species. Moreover, not all plant species and varieties have the same sensitivity to polyphenols and terpenes.

Several practices can limit these allelopathic effects :

• Wait at least 6 months before sowing crops.
• Prefer applying RCW as mulch rather than incorporating it into the soil. Incorporation favors contact of polyphenols and terpenes with roots.
• Avoid tree species that contain many tannins and terpenes for RCW production (see "Choice of species" paragraph).
• Perform the watercress test (germination of watercress seeds) to detect possible allelochemical compounds.

Nitrogen hunger

Nitrogen hunger on a potato plant

During wood decomposition, some bacteria consume part of the nitrogen present in the environment. There is then competition for nitrogen resources between the plant and microorganisms. This results in growth slowdown and leaf yellowing. This nitrogen hunger phenomenon is temporary and lasts on average 6 months. Nitrogen immobilized in microorganisms is then gradually released into the soil for crop use. Nitrogen hunger is measurable and predictable. The amount of nitrogen immobilized by microorganisms can be estimated at one nitrogen unit per 1 m³ of RCW humification. Nitrogen hunger is too often blamed as the main factor responsible for crop depression, overshadowing other possible causes. Nitrogen hunger should not occur without RCW incorporation into the soil.

To ensure nitrogen hunger is not an obstacle to RCW success, several technical routes are possible :

• Sow a legume (white clover, alfalfa, pea, lupin…) together with RCW use or one season before RCW establishment.
• Compensate with a nitrogen-rich fertilizer as a last resort. However, excess nitrogen can disrupt nitrogen mineralization and promote nitrophilous weed development. Approximately 1 kg of nitrogen per m³ of RCW is needed. The amount of nitrogen (from fertilizers and mineralization) immobilized by soil microorganisms can also be estimated by the following calculation : %N immobilized = 27% soil N + 7.5% / cm of RCW.

The table below shows the percentages of nitrogen temporarily unavailable due to soil life depending on the amount of RCW applied to the soil according to the above formula :

Source : B. Noel

RCW quantity	% N immobilized (fertilizer and mineralization)
1 cm = 100 m³/ha	34.5%
2 cm = 200 m³/ha	42%
3 cm = 300 m³/ha	49.5%
4 cm = 400 m³/ha	57%

Thus, for an application of 300 m³/ha of RCW, it is recommended to double nitrogen fertilization of crops to compensate for nitrogen made unavailable during the first year of RCW use.

RCW production

Choice of species

Not all tree species are equivalent for RCW success.

Several recommendations for tree species choice favor RCW success :

• Use tree and hedge species locally available on site to avoid RCW transport.

• Where possible, use diversity of tree species available for RCW production.
• Favor deciduous trees over conifers with a maximum of 20% conifers to limit allelopathic effects due to conifer terpenes. Species rich in tannins (acacia, oak, beech,...) should also be avoided. Allelopathic effects are less marked with white wood species such as poplar or birch.

Branch harvesting

RCW can be produced from tree and hedge pruning residues. It is recommended to harvest young branches of less than 2 years (ideally one year). Their diameter is less than 7 cm. The smaller the diameter, the richer they are in mineral elements. Lignin in young branches is still polymerizing, which gives them some flexibility and facilitates wood degradation by fungi.

Harvest period

Branches should be harvested in autumn or winter (between October and March) for several reasons :

• It is the dormancy period of trees. Branches are the richest part of the tree in nutrients (minerals, amino acids, proteins,…) in autumn, after leaf fall. Indeed, leaves fall after returning half of their mineral elements to branches. 75% of tree nutrients are contained in branches with diameter less than 7 cm. These resources stored in branches can be mobilized by the tree the following spring for bud and new branch production.

• Autumn is also when nitrogen is abundant in soils, limiting nitrogen hunger.
• The cover formed by RCW protects soil fauna and flora from frost.

Volume of harvested branches

The table below provides an estimate of the number of trees to prune and the time needed to obtain different volumes of RCW (1 and 150 m³). Working time includes tree pruning and branch stacking.

Indicative data from an RCW production experiment in agroforestry conducted in 2011

RCW volume	RCW mass	Volume of branches cut	Number of trees pruned	Working time
1 m³	0.2 tons	2 m³	2	26 min
150 m³	34 tons	304 m³	187	64h12

Wood shredding

Basidiomycete fungi cannot penetrate tree bark. Wood fragmentation increases the exposure surface of wood and initiates colonization of exposed wood by fungi capable of degrading lignin. Fragment size should be between 5 and 10 cm. The smaller the size, the better the biodegradation and its effect on the soil.

RCW shredding. Antoine Chedru

A mechanical wood chipper is an expensive investment that can be reduced by purchase through a CUMA or rental.

This step can be done using a hammer mill (rather than a knife chipper). Choosing the smallest mesh size for the calibration grid allows obtaining a very fine chip.

Sorting waste (plastics, for example) sometimes present in branches before shredding can be useful.

The table below provides an estimate of the working time needed to shred the volume of cut branches. Shredding duration can vary from 10 minutes to one hour per m³ of wood. This duration can vary greatly depending on chipper capacity.

Indicative data from an RCW production experiment in agroforestry conducted in 2011

RCW volume	Volume of branches cut	Shredding time
1 m³	2 m³	16 min
150 m³	304 m³	39 h

Limit storage duration

RCW should be used as soon as possible after shredding. If it is not possible to use RCW immediately after shredding, it is recommended to store it sheltered from weather for a maximum of a few weeks. Low winter temperatures limit biological degradation of wood during storage.

Obtaining RCW

When RCW cannot be produced on site, it is always possible to contact municipal services, tree pruners, or landscapers to obtain it.

Shredding residues must not have been chemically treated after felling to comply with Organic farming regulations.

Production costs

The estimated production cost of RCW is €18/m³. It includes costs of the different production steps : pruning and stacking, shredding, transport and/or storage. This cost remains almost the same whether shredding is done by an external service or by oneself using a rented mechanical chipper.

When shredding is done by an external service, expect about €8/ton of RCW, i.e., €2/m³.

Chipper exchange and rental service

RCW Génération is an online service to find RCW and chipper rental: https://www.brfgeneration.fr/

RCW use

RCW is an effective tool to enrich soils in organic matter provided it is used wisely. Feedback recommends conducting soil analyses to ensure regular monitoring of soil biological activity during RCW implementation.

Required quantities

In temperate climate, a self-fertile forest or grassland soil contains on average 8% humus over 30 cm depth. In theory, the annual quantity of RCW to apply to reach 8% humus in an agricultural soil would be 100 m³/ha, i.e., a 1 cm layer on the soil. This also corresponds to applying 300 m³/ha, i.e., a 3 cm layer to be renewed after 3 years.

Experience feedback generally recommends :

• A volume of RCW of 30 to 300 m³/ha, i.e., a 0.3 to 3 cm thick RCW layer. This quantity is often determined by the limited amount of available wood.
• A renewal frequency of 1 to 10 years, to be adapted according to crops, soils, and production goals.

The table below gives an estimate of the volumes of cut branches, number of trees to prune, and working time needed to produce enough RCW to cover 3 cm layers on areas of 500 m² and 1 ha of soil.

Indicative data from an RCW production experiment in agroforestry conducted in 2011

Area to cover (over 3 cm thickness)	RCW volume	RCW mass	Branch volume	Number of trees pruned
500 m²	15 m³	3-4 tons	30 m³	18-19
1 ha	300 m³	68 tons	600 m³	373

Working time includes stacking, shredding, transport and/or storage, and downtime (breaks,...).

Market gardening

The simplest route, recommended in market gardening, is to apply 3 cm of RCW, i.e. 300 m³/ha every 3 years. To avoid nitrogen hunger (when RCW is incorporated into the soil), an autonomous nitrogen legume, such as fava bean, can be sown. Another solution is to double the nitrogen fertilization of crops in the first year following the application of RCW.

Field crops

In field crops, a lower input of RCW of 40-50 m³/ha is recommended. Experience feedback recommends a renewal every 6 years because the decomposition time can be long. The use of RCW in field crops can pose difficulties for export and industrial processing. Undecomposed RCW fragments can be incorporated into the harvest and later found in processing equipment (in sugar factories, in brushes for flax fibers, etc.).

Equipment

RCW spreading can be done using a manure spreader (with spreading table).

To limit compaction caused by agricultural machinery, spreading can be done perpendicular to the usual passage direction, directly on stubble, on frozen soil in winter, or on dry soil.

Application as mulch or incorporation into the soil

RCW spreading as mulch without soil incorporation. Antoine Chedru

RCW can be used as mulch or superficially incorporated into the soil without turning it over by harrowing (spring harrow rather than disc harrow). Several passes may be necessary. Incorporation should preferably be limited to the top 10 centimeters of soil. However, some feedback reports good results obtained with incorporation at 12 cm using a rotary plow or a rotary tiller with straight blades (combined tool). Fungi capable of decomposing lignin do not survive in depth where oxygenation is reduced. Poor wood decomposition and accumulation of organic matter at depth would favor oxygen-consuming bacterial activity and could lead to root asphyxiation. Incorporation at shallow depth allows RCW decomposition in the presence of oxygen and under good moisture conditions (between 60 and 100%).

Both RCW application methods have their respective advantages and disadvantages :

	Without incorporation	With incorporation
Decomposition rate	Slowed	Fast
Nitrogen hunger	Less significant	More significant

In soils where biological activity and structural stability are not optimal, soil incorporation is preferred during the first use of RCW.

Precautions

• Never bury it;
• It is preferable, to start the machine, to apply it before a large cover of legumes or a legume in crop so that the system begins to stabilize between the nitrogen need for the degradation of this RCW and a possible nitrogen hunger on the crop in place (which is avoided by establishing a legume);
• Apply RCW in quantity: depending on the quantity available, prefer to apply it in a single plot to reach tonnages on the order of 20 - 30 t/ha rather than trying to sprinkle a little everywhere with the aim of correcting the organic matter content (1 ton corresponds to about 2 - 3 cubic meters of RCW);
• Perform a liming amendment so that the biological activity can structure the soil by using calcium and humus.

Forest litter supplement

In degraded soils where biological activity is very low, it may be necessary to reintroduce soil organisms involved in wood decomposition trophic chains. Adding forest litter at a rate of 10 to 20 g/m² of forest litter is sufficient.

Sowing

Sowing can be done immediately after RCW incorporation, using a standard seed drill. In no-till seeding, RCW can be applied without incorporation when biological activity and soil stability are sufficient.

Use of RCW as livestock bedding

RCW must be used quickly after shredding and stored under a tarp protected from the weather, if necessary. The recommended volume of RCW for a 100 m² barn is 1.5 m³ of RCW/day. One m³ of RCW is equivalent to 40 kg of straw. The RCW manure can be composted at the edge of fields before spreading.

Photo gallery

This article was written with the kind participation of Francis Bucaille, Olivier Tassel and Antoine Chedru.

Sources

• BRF, 2022, AgroLeague
• Precautions for using RCW in agriculture, AgroLeague
• B. Noel, P. Frenay. 2006. RCW and aggradation. [05/10/2022]. https://www.youtube.com/watch?v=3hQ1AymcWws
• Bucaille, F. & Selosse, M. A. (2020). Revitalizing soils: Diagnosis, fertilization, protection. Dunod.
• Le Monde. How to use B.R.F. (Ramial Chipped Wood) in the garden?. https://jardinage.lemonde.fr/dossier-934-utiliser-brf-bois-rameal-fragmente.html
• Permaculture Design. Mulch in permaculture. https://www.youtube.com/watch?v=9HsmDs5cIlU
• Sikana Nature. What materials for RCW? | Sustainable agriculture (Ramial chipped wood). [05/10/2022]. https://www.youtube.com/watch?v=-_43CWwPb6M
• Sikana Nature. How to use RCW (Ramial Chipped Wood) | Sustainable agriculture. [05/10/2022]. https://www.youtube.com/watch?v=J4tuFtVdnhU