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Case Study

Increasing brassica crop trash breakdown with the application of biostimulant Digester

BioStart Limited.
Sam Drass, Pukekohe, Auckland.

May 2008

Key words
Brassica, crop trash, breakdown, Digester, nutrient availability.


  • A block of broccoli was divided into 2, half was sprayed with 4lt/ha of Digester after being cultivated the other half was left untreated.
  • Weather conditions over the winter have been extremely wet.
  • DHM Lab’s soil and soil microbial indicator test were used to measure microbial and nutrient levels.
  • Faster trash breakdown improves nutrient recycling and soil structure.


Soil Microbial Indicator Test results

UntreatedDigester% increase
Total microbial count12,811 kg/ha10,761 kg/ha-16%
Bacterial count5,111 kg/ha3,111 kg/ha-39%
Fungal count2,500 kg/ha3,750 kg/ha+50%
Yeast5,200 kg/ha3,900 kg/ha-25%
Anaerobic count222 kg/ha111 kg/ha-50%
Azobacter500 kg/ha333 kg/ha-33%
Actinomycetes444 kg/ha56 kg/ha-87%
Fungi: Bacteria ratio1.5:12.5:1
Fungi: Yeast ratio0.5:11:1


  • Total microbial count is higher in the untreated block. This is driven by the higher bacterial levels. This indicates that the untreated block is still going through the decomposing process.
  • The lower total microbial count and bacterial count for the Digester block indicates the decomposition process has been completed.
  • The higher combination of anaerobic and yeast levels in the untreated block also point to a slower rate of decomposition.
  • The reduced numbers of Actinomycetes in the Digester block indicates the decomposition process has been completed.
  • The Digester block’s bacteria:fungi and fungi:yeast ratios are both in the desired range compared to the undesirable range for the untreated block.

UntreatedTreated% increase
Cation Exchange Capacity19.7524.10+22%
Organic Matter6.08%6.77%+11%
Base saturationUntreatedTreated% increase
Total base saturation66.92%72.90%+9%
Major elementsUntreatedTreated% increase
Mehlich Phosphate143.37kg/ha157.63kg/ha+10%


  • Digester increased Cation Exchange Capacity. However this increase hasn’t diluted nutrient levels in terms of base saturation or altered soil pH. In other words hydrogen hasn’t rushed in to occupy the vacant sites on the soil colloid, driving down the pH.
  • Digester has increased calcium phosphate, magnesium and potassium levels in the soil.


  • The application of Digester has sped up the decomposition of trash and increased soil mineral levels of calcium, phosphate magnesium and phosphate.
  • Digester has improved CEC and base saturation without altering soil pH.
  • The heavy rain and wet soil conditions has not impacted on the Digester treatment.
  • The Digester block is ready for planting while the untreated block is still 2 weeks from completing decomposition.

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