Composts & biochar - report 1

25 August 2012

Who came?

We had a small group of local growers gather to examine the trials and how they were set up. Also present were Bruce Pearce from Organic Research Centre (ORC) to give a researchers 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 and why growers might be interested in experimenting with it.

Setting the scene

As the group had come together halfway through the trial this is not a typical of how a Field Lab would normally work, but we decided to try and combine some of the initial thinking that might go into a trial and then look at how Pete’s trial compared.

After hearing about what might be the benefits of using biochar in compost and the soil the groups spent a little time imagining they were at the beginning of the trial process and how they would work out setting up a trial.

What were we trying to find out?

The starting point was to see what information was already out there and identify the gaps, we all recognised that there is a risk of re-inventing the wheel by not doing homework before starting a trial. Once a gap in knowledge (either within the trial group or more widely) has been identified you can start to narrow the focus of the experiment.

What became very quickly apparent was that different groups had different expectations and priorities:

  • Researchers - want as many replications as possible
  • Grower - wants trial to fit easily into growing and  harvesting programme
  • Company - wants to see how product works in commercial situation

Negotiation and compromise

The setting up of a trial requires some negotiation and compromise between the different parties to ensure a useful yet achievable experiment. Also WHO has control of the trial? (ORC mentioned a trial where they had turned up to measure the yield of a trial crop only to find it had been harvested the day before). Where growers are not being paid to conduct the trial this balance is not always easy.

Parameters for trial at Hankham that needed to be agreed.

  • Do we trial on annuals or perennials?
  • How can we ensure continuity of treatment (for instance in different crops or where a large number of staff is caring for a crop?
  • Accounting for the edge effect on a crop - in field scale trials this is not a big problem but for Hankham who have small areas of a large number of crops this could negate the results.
  • How many replications are feasible in a commercial setting - too many and the grower’s commerciality is compromised, too few and the scientific rigour of the trial is likewise affected.
  • What are we actually going to measure, how easy are these to take and how useful is that information, e.g.
    - Yield
    - Water use
    - Quality
    - Reduced cost to achieve the same results
    - Grower observation

Vital to the success of the any experiment (as Bruce kept reminding us!) is: 'What is the research question??'

Some shortcomings of the trial - and suggestions for improved trial next year

It became clear that the trials with Carbon Gold had perhaps been set up with too wide a focus. So for instance of the initial 28 proposed triallists a number were unable to take part due to the awful growing season, others started but for a variety of reasons did not do full trials. This left a core of around 12 growers that got some meaningful results from the trials. However on top of this, different growers focused on different aspects of the trial or were so different as to be un-comparable, for instance:

  • Propagation vs. soil fertility
  • Lettuce vs. cucumber vs. cabbage
  • Light sandy soil vs. heavy clay
  • Glasshouse vs. out door

What this meant was that for any particular result or observation there might only have been 2 or 3 replications. Although this is still of interest it may not provide any definite proof for the trial.

What were the interim results of the trials at Hankham (some crops were still in the process of propagation or growth).

Some feedback from trials so far – full results at final meeting in November

Pete found that the composts broadly behaved similarly for most crops.

Germination was good in both the Carbon Gold compost and his own compost with added biochar. The coir based biochar compost did not hold onto nutrient quite so well as his homemade one, but since he uses a liquid feed in his propagation system to ensure strong healthy plants this did not cause a huge problem.  Adding biochar to his own compost made a marginal improvement to the performance.

Adding biochar to the peat based compost had no effect.

Generally he found that lettuces and brassicas did well with the biochar, with other crops there was less difference or even (for instance Aubergines) worse.


Field lab - Soil analysis – its use and interpretation
16 March

Tolhurst Organic Partnership C.I.C., West Lodge, Hardwick, Whitchurch on Thames, Pangbourne RG8 7RA

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