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Ramial chipped wood (RCW)

Small-diameter branches, chipped, brought to the soil as mulch or mixed into its surface to feed its life.

Explanation

RCW is made of small-diameter branches, chipped. The technique was born in Canada and aims to bring cultivated soil closer to a forest soil; recommendations mainly concern branches under 7 cm in diameter (Barthès, Manlay & Porte, 2010, review published in Cahiers Agricultures). The term names both the material and the technique. Spread as mulch or mixed into the top few centimetres of soil, it stimulates biological activity and adds organic matter to the soil; when buried, it can first penalise the next crop, especially in sandy soil.

Refined definition

The review by Barthès et al. (2010) brings together published trials, in temperate and tropical climates, whose results are statistically significant. RCW generally has a positive effect on yield there, except for the crop that immediately follows a first burial in sandy soil. Especially as mulch, it improves soil moisture, porosity and structure, enriches the soil in organic matter, stimulates its biological activity and increases nutrient availability in the medium term. The review sets apart, among neighbouring practices, mulches of wood chips that probably do not come from branches.

Key points

  • The first-year dip

    On a sandy-gravelly soil in Canada, yields fell in the first year after burying RCW (wheat), then were mostly higher than the control's in the following years. The review's authors explain this dip by nitrogen immobilisation by the soil microflora (what gardeners call “nitrogen hunger”), which an input of nitrogen, mineral or organic, can offset; immobilisation is stronger with fresh RCW than with composted RCW. As mulch, even on sandy soil, the effect on yield was positive from the first crop: a result obtained in a tropical climate, still to be confirmed in a temperate one (Barthès et al., 2010).

  • What the review cannot say

    Effects vary with the tree species used and the way it is applied (amount, frequency, chip size), and the available results hardly allow precise recommendations. The benefit of RCW compared with non-woody amendments is poorly documented, and that of a nitrogen-rich RCW, from legumes, is not established (Barthès et al., 2010).

Watch out for

  • • Burying RCW just before a crop, especially in sandy soil, risks a lower harvest for lack of nitrogen: offset it with a nitrogen input, or prefer mulching, which gave better results from the first crop in tropical trials (Barthès et al., 2010).
  • • Extracts of fresh RCW from broadleaves and conifers reduced the germination of cress, an effect attenuated after composting (Beauchemin et al., 1992, cited by Barthès et al., 2010): as a precaution, it is not spread over seedlings.

Examples

  • • RCW mulch at the foot of shrubs and fruit trees
  • • Hedge prunings, chipped
  • • RCW spread over a resting bed, well before growing on it

Sources

  • Barthès, B.G., Manlay, R.J. & Porte, O. (2010). Effets de l'apport de bois raméal sur la plante et le sol : une revue des résultats expérimentaux. Cahiers Agricultures, 19(4), 280-287.