Composts & biochar - report 2

10 November 2012

Who came?

We had a small group of local growers gather to examine the results from the trials, how they were set up and how we could improve upon them for next year. Also present were Bruce Pearce from Organic Research Centre (ORC) to give a researcher's view of the trials and how they might have been improved, Euan Brierley from the Soil Association was facilitating the meeting and Craig Sams of Carbon Gold gave an introduction to the group on biochar.

Setting the scene

This was the second of two field lab events at Hankham Organics, the growers who attended this event were not the same as those that had come to the first lab, so some ground was covered again hearing about what might be the benefits of using biochar in compost and the soil. The group then quickly got down to looking at the trials and trying to learn not just about how the composts had performed but also how we could improve on the design trial.

Trial results

Please email Ben Raskin on for the full trial results but some of the highlights were:

1. Results to date of the trials comparing GroChar propagation composts with other propagation composts routinely used here at Hankham Organics.

  • Lots of potential for the GroChar seed compost, particularly brassicas (cabbage and Pak Choi) seemed to respond well. Longer-term fertility may be an issue but germination is generally good compared to other propagation composts and fertility is easily augmented with liquid feeding, as demonstrated on the leaf beet trials.
  • The compost was easy to use in terms of both handling when filling and sowing trays and watering. It was not easy to waterlog, did not dry out nor inhibit germination in any way. The root systems on plants were good and comparisons of this aspect could be considered for the future.
  • It is possible that the GroChar compost needed slightly less water than the peat and wood compost based mixtures, less watering may have allowed the compost to retain more nutrient.
  • GroChar compost compared well against fertile fibre and melcourt but only in the Pak Choi trial was it better than Klasmann composts. Generally it did not perform as well as Klasmann module compost but considering that it is peat free I personally felt it was a worthy contender.
  • In the leaf beet and cabbage trials GroChar out performed fertile fibre, although both are coir based. It could be that the GroChar soil improver content helped to retain nutrients, water and a microbial fauna more effectively.
  • The limited trial of the potting compost was not favourable for GroChar but more trails would need to be done with this to draw any firm conclusions.

2. An interim report on the first stages of the GroChar soil improver trials where it has been applied to glasshouse soils.

  • Soil amendments were inconclusive so far but I suspect that it would take time for any differences to show up anyway. The slight improvement seen in the Pak Choi bed could be attributed to the good start obtained with the compost.

3. Lessons learned from these trials and others and how these can be used to improve future trial technique and scientific validity.

a. Propagation Technique:

In order to maintain consistency throughout the sowing and propagation process it is important that:

  • Trays have been thoroughly washed to reduce interference by disease.
  • All seed are from the same batch (check there are enough beforehand).
  • The same person sows all trays in the same way on the same date.
  • Trays are labeled well and good records are kept of dates and quantities.
  • The trays are subject to identical treatment i.e. water, heat, light.
  • Any edge effect is either eliminated or made the same for each tray.

b. Photography:

  • It is important to ensure light levels stay the same between shots as this can greatly affect the ability to compare them. Pictures should be taken when either the weather is settled or in a shady spot with the use of flash.
  • The distance from the subject and the field of view must be consistent.
  • Each shot needs to be tagged and dated; it is very difficult to keep track of the trials effectively unless the actual picture file carried this information.
  • Ideally take photos at a minimum of one week intervals throughout the propagation process. This will allow comparison of germination as well and maturation.

c. Root Comparison:

Future trials could include other aspects such as root health and general disease resistance. Again photography could be used to compare roots and plant health, as long as a representative sample was used. Perhaps a sacrificial batch could be left in trays until the plants expired and then compared to determine which one provided the best habitat for longest?

d. Trialing within a commercial setting:

From a commercial perspective there seem to be two ways to achieve robust results without placing undue pressure on the business.

  • Use an easy and simple technique with relatively low accuracy and get multiple replications to give meaningful results.
  • Develop a stringent and controlled method providing more confidence in the result but that is implemented only once or twice.


NEW Field Lab: Improving the targeting of mastitis treatments
29 January

The George Inn, The Square, Mere, Wiltshire, BA12 6DR

Field Lab: Cultural methods to control black grass
24 March

Shimpling Park Farm, Shimpling, Bury St Edmunds, Suffolk, IP29 4HY

Supported by...

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Prince of Wales's Charitable Foundation

Organic Research Centre