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Optimised compost management for productivity and soil health

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It is widely accepted that compost can help capture carbon, retain nutrients, and reduce the dependence on bought-in fertiliser by improving the soil structure and biology. But how can you get the best out of your compost? And what benefits can you expect?

Five growers in Cornwall will explore how compost quality and therefore yield, can be influenced by a wide range of management variables.

The field lab is the first of three to run as part of the five year Lottery Funded Farm Net Zero Project, a major project from the farming community in Cornwall to explore the contribution that agriculture can make to achieve Net Zero.

The benefits

The group are aiming to find out what changes in nutrient availability and pH take place over time. They are also interested in looking at which practices ensure low risk of pathogens and weeds, and the effect of different compost 'products' on soil health and yield. By getting compost techniques right, growers hope to reduce the dependence on bought-in fertiliser, have less waste, reduce weed burden and improve the structure and biology of their soils.

Trial design

The group are monitoring the following over five different holdings: 

  • the impacts of turning according to temperature rather than on a timed schedule.
  • adding biochar, bokashi, and bespoke microbial concoctions.
  • the longevity of weed seeds and pathogens in compost.
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Can you safely compost weed seeds and diseased material, without worrying about spreading it around your holding?

With plant diseases increasingly prevalent, growers are concerned about spreading diseases further by composting disease-infected material. The same goes for pernicious weeds: nobody wants to be spreading dock and bindweed around their holding through the compost.

One member of the group decided that their main priority for the trial was to find out whether they could safely compost weed seeds and diseased material, without worrying about spreading it around their holding. They filled bait bags with weed seeds and materials infected with a specific plant disease, and buried them in the compost for 12 weeks to see what happened.
Bait bags

The bait bags contained: an iButton (to monitor temperature & humidity), a penny (to allow detection with a metal detector), weeds to kill (Oxalis & bindweed), seeds to kill: (dock & parsnip - a proxy for dock due to similar seed size but more reliable germination) and 5 diseased leaf strips. 
Bait bag contents

They tested the temperature of the heaps regularly throughout the process. The trial lasted for 140 days, and fitted with the standard management of compost in a holding bay.

Compost was turned with a loader at weekly intervals but turning involved careful moving of compost in such a way that material was both within the compost heap and on the edge over the full trial. Mean temperatures peaked in the fourth week at 68°C despite weekly turning, and were averaging 41°C at the end of the trial. Control samples were kept in a fridge for the same amount of time. All data was fully replicated.
The results

The results were fantastic: Composting killed this specific plant pathogen but the control samples remained viable. Further, weed propagules were turned to dust (bindweed and oxalis) but the controls are very viable. Early results indicate that the seed controls are germinating, but failing when entering the composting process.  It is important to note that only one disease pathogen was trialed, and hot composting will not kill all pathogens.

Other results

No impact on worm number has been identified yet, and aggregate stability assessments are on-going. We are planning to assess biological activity of the soils after compost application – an about turn from the original proposal where soil assessments were going to just be nutrient-focused. The other triallists will be carrying out the same trials on their compost heaps next year

The compost field lab trialists met up to review progress, and plan next years next stages. With harvesting of vegetables grown with different compost treatments under way, some initial anecdotal outcomes and Brix meter results are beginning to add to the groups understanding of what is happening. The next step is to do a soil analysis following compost applications.

The first stage of the trial results will be available soon. The effect of compost treatments on weed seed and bindweed survival in composts will be assessed using electronic temperature recorders to track  effect of different treatments on compost heaps. 

The Prideaux Gardens trial site has planted out mixed lettuces on their trial plots.  The 3 compost treatments are: bokashi, biochar, and bokashi + biochar.  The trial area has been divided into multiple 1m2 plots, with a buffer strip between, each with a different treatment of compost or a control of untreated compost.  These  have been planted out with mixed lettuces.  Their growth will be monitored using Brix meters to measure the sugars in the leaves.

Trial plots at Prideaux gardens planted with mixed lettuce
Trial plots at Prideaux gardens planted with mixed lettuce


Setting up compost bins and treatments

December 2022

Put together bait bags at Helligan

April 2023

set up trial plots and plant out

May 2023

Crop and soil assessments

Summer 2023

Make compost for 2024

December 2023

Compost application

March 2024

Plant up compost plots

May 2024

Soil and crop assessments

Summer 2024

Final assessment and report

October 2024

Group Coordinator

A portrait of Jerry Alford.
Jerry Alford

Soil Association

Bristol / UK-wide

Arable & Soils Advisor at Soil Association, and farmer. I ran the family farm in Devon for 25 years, farming dairy, then organic beef, sheep and arable units with holiday cottage conversions. Former chairman of a local farmer owned co-op grain store, and involved in the grain supply chain nationally.


A portrait of Amelia Lake and Chloe Binns.
Amelia Lake and Chloe Binns

Real Food Garden


A portrait of Emma Beddard.
Emma Beddard

Prideaux Gardens


A portrait of Nicola Bradley.
Nicola Bradley

Lost gardens of Helligan

St Austell

A portrait of Loretta Francia and George Henry.
Loretta Francia and George Henry



A portrait of Kate Maciver-Redwood.
Kate Maciver-Redwood

Haye Farm-on-River Tamar



A portrait of Hannah Jones.
Hannah Jones

Trifolium Services

Southwest England

In this section you will find reports and results from the field lab, as well as other relevant documents.