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Case Study

Increasing apple leaf litter decomposition with the application of soil biostimulant Digester

Stephen Wrigley, BioStart Limited Auckland.
Gerard Besamusca, AgConsult Waihi.
Karin Watson, BioCult Lab Cambridge.
Tim Herman, Fruitfed Supplies Hastings.
Brian McLay, Hastings.

July 2003

Key words
Leaf litter, Digester, Mycorrhizae, Nitrogen.


The trial was run in a block of mature Fuji in Twyford, Hawke’s Bay. Leaves were collected on 18 July 2003 and spread between wire mesh cages which were put back onto the orchard floor and pinned to the ground.

Treatments used were:

  • Control - Nitrogen 30kg/ha 
  • Digester 2lt/ha
  • Digester 4lt/ha 
  • Digester 2lt/ha + Nitrogen 30kg/ha

Treatments applied 23 July. Water rate was 250 L/ha.

Photos were taken of the cages 3, 44, and 100 days after application

Root samples were collected from 6 trees in each treatment and send to BioCult  Laboratories to determine mycorrhizal colonisation rates.



  • The results show that 3 days after application there was no difference between the various treatments and control.
  • At the end of the trial 100 days after treatment there were some clear differences. The 4lt/ha Digester and the 2lt/ha Digester + 30kg/ha Nitrogen had clearly increased the rate of breakdown.
  • Both the 4lt/ha Digester and 2lt/ha Digester + 30kg/ha Nitrogen were statistically significant. 


TreatmentRoot branches/gm% Ecto colonization% VAM colonizationComments
Control~8050%13%No EM layer on fine roots, only some on thicker roots. No clusters.
30kg/ha Nitrogen~10050%27%Again thinner layer of EM. Some loose clusters.
2lt/ha Digester~150100% on fine roots27% hard to assess with thick EMDese cluster of pine like EM antlers growing directly off main roots.
4lt/ha Digester~12072%53%Less dense clusters, long fine roots, thinner EM layer.
2lt/ha Digester + 30kg/ha Nitrogen ~8060%7%Much thinner layer of EM on fine end roots. No clusters.
  • Both Digester treatments have had a significant  mycorrhizal response.
  • The addition of Nitrogen has suppressed the mycorrhizal  response caused by the Digester.


  • 4lt/ha Digester and 2lt/ha Digester + 30kg/ha Nitrogen accelerated leaf litter decomposition.
  • 4lt/ha Digesterand 2lt/ha Digester increased Mycorrhizla colonization and root branches.

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