Using digestate as a component of soil manufacture

Project name: Bodmin trials

Project period: March 2012 - March 2013

Situated in Cornwell, this project investigated the use of whole digestate as a component of manufactured soils for use in the housing sector. It included a field trial that blends site won aggregates derived from china clay workings, with PAS 110 digestate and PAS 100 compost to manufacture soils for amenity and sports turfs and allotments.  A separate trial examines the use of digestate in tree pits.


Trial Design

The fully replicated field trials consisted of manufacture soils for sport, amenity and allotment soils and comprise of the following:

Sports turf plots  

1. Control (no amendments)

2. Digestate + PAS 100 compost @ 400 tonnes/ha 

3. PAS 100 compost @ 400 tonnes/ha 

Amenity turf plots 

1. Control (no amendments)

2. Digestate + PAS 100 compost @ 200 tonnes/ha

3. PAS 100 compost @ 200 tonnes/ha (only)

Allotment soil plots planted with potatoes

1. Control (no amendments)

2. Digestate + PAS 100 compost @ 100 tonnes/ha

3. PAS 100 compost @ 100 tonnes/ha

 

The tree pit trial will be planted with silver birch and also comprises three treatments:

1. Control

2. BS3882:2007 topsoil

3. Manufactured soil  

 

Monitoring

At the end of each growing season, the growth and health of the vegetation on each of the treatments will be measured. Soil samples will be taken and analysed for chemical and physical characteristics. The project also includes an economic assessment that aims to determine the commercial viability of digestate use in soil manufacture.
 

Results

Monitoring of plant growth was carried out in autumn 2012 across all treatments by taking samples of the established vegetation or in the case of the potato crop, the ground was dug and tubers collected.  The vegetation samples were dried and weighed and the tubers were counted and weighed.  Compared to the control plots there was a significant uplift in vegetation growth and tuber growth on plots that were treated with compost only or treated with a combination of compost and digestate. On the amenity turf plots, it was also observed, that that there was marked increase in biomass where digestate had been applied.  This was not as pronounced on the sports turf plots probably due to the presence of clover.

The findings of the trial demonstrates there may be some benefit from using whole digestate in combination with compost where rapid sward growth is required.  Nevertheless the additional costs associated with transporting the digestate to site and then blending it with the onsite materials may negate the agronomic benefits that can be derived from it.  Fibre digestate may be more suited to such an application.