Digestate in Horticulture (Ornamental Plants & Strawberries)

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Dr Mary Dimambro, Managing Director at Cambridge Eco Ltd has worked on several reports with WRAP about the use of digestate in horticulture. The aim of the reports were to develop appropriate markets for quality digestates to be used in horticulture. There were three reports written which have been summarised below.

Dr Mary Dimambro will be speaking at the R&I Forum 2017, to find out more click here.

Digestate use in protected horticulture

In a literature report written by Dr Mary Dimambro, Dr Joachim Steiner and Dr Francis Rayns.

Summary

In this report, evidence worldwide regarding the use of whole, separated liquor and separated solid (fibre) digestate from AD in protected horticulture is reviewed. A wide range of studies was found including over 45 edible crops and ornamentals, with digestate used in a number of ways, predominantly in hydroponics, as a liquid fertiliser and as a growing media ingredient. In some studies, digestate in combination with other standard industry ingredients was shown to achieve similar or improved plant growth, quality and yield, provided the recommended nutrient and electrical conductivity levels are considered.

Large scale adoption of digestate within the protected sector could show a decrease in the use of peat and inorganic fertilisers, however currently, protected horticulture is not a permitted end use for waste-based digestates falling under the AD quality protocol, even when PAS110 certified. Hence this presents a significant barrier to the uptake of digestate in protected horticulture in the UK. 

Bark admixtures: Formulation and testing of novel organic growing media using quality digestates for the production of containerised plants.

This report is written by Dr Mary Dimambro, Dr Joachim Steiner, Dr Russ Sharp and Sam Brown.

Summary

DEFRA and DECC identified the need to develop appropriate markets for quality digestate which could be used in ornamental plant horticulture. In this report, the effects of digestate used as an ingredient in the commercial production of potted plants was assessed. The plants chosen were cyclamen, black pine and fern, to represent a range of ornamental species grown in the UK.

The 4 whole and liquor digestates used in this experiment were mixed with bark and other peat free ingredients used in growing media to create 20 admixtures. The highest digestate quantity was considered very high and for trial purposes only. Two standard commercial growing media were used as controls. Plants were grown in the admixtures for at least 90 days. The results found that;

• For cyclamen, there was no impact from using digestate.
• For fern that:
  • The two admixtures with the highest quantity of food waste digestate caused a reduction in chlorophyll, growth and leaf quality, which was attributed to the high salt content.
  • Food based digestate admixtures of lower doses had no impact. No effects were observed for the potato waste and maize digestate admixtures.
• Black pine plants grew as well in the digestate admixtures as the controls.
• Liverwort growth was suppressed when using digestate admixtures, compared to using peat growing media.
• The digestates provided valuable plant nutrients and so no additional fertiliser was required.
• Cost competitive potential based on cost-benefit analysis at the time of the report being released; the price of peat fluctuates greatly.
• Using bark and digestate based admixtures is more sustainable than using peat based growing media

For further information, please read the document here.

Use of quality digestates as a liquid fertiliser in the commercial production of strawberries.

This report is written by Dr Mary Dimambro, Dr Joachim Steiner, Rob Lillywhite and Dr Catherine Keeling.

Summary

DEFRA and DECC’s AD strategy plan was developed to increase the uptake of digestate in horticulture. This Cambridge Eco led report looks at the use of digestates as liquid fertiliser in UK strawberry production. The six digestates used reflect the variety of feedstocks of UK digestates: Potato waste, slurry, food waste, maize and a mixture of maize, manure and milk waste were used. The digestates used were either whole or the separated liquor fraction. Digestates were diluted 25-51 times to achieve commercial standard levels of nutrients, suitable for supporting strawberry plant growth. Some minor amendments were then made to optimise the nutrient solution profile. The strawberry plants were trickle irrigated with the solutions.

The investigation found significant differences in strawberry yield and fruit quality comparing the six digestates and a standard commercial fertiliser:

• Out of the six digestate mixes used; 3 x performed as well as the control for total fruit yield and class 1 yield. Of these, the food and slurry based digestate outperformed the control for fruit taste.
• 3 x digestates had very slightly reduced yields, but this was only significantly lower for one digestate. Of these 3, all out performed the control in terms of fruit flavour.  

Currently, protected horticulture is not a permitted end use for waste-based digestates falling under the AD quality protocol, even when PAS110 certified. Hence this currently presents a significant barrier to the uptake of digestate in protected horticulture in the UK.

Dr Mary Dimambro, Managing Director at Cambridge Eco Ltd, will be speaking at the R&I Forum in March 2017, to find out more click here.