Design and Evaluation of Peat-Free Blocking Media

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The production of field vegetables and salad crops is highly dependent on transplanted seedlings that are grown in media often containing peat. The mining of peat has adverse environmental consequences including the release of CO2, biodiversity loss and increased risk of flooding and is being phased out by the UK government. Commercial peat-free growing media have been developed, however whilst these are suitable for use in plastic modular trays they are not cohesive enough to produce the larger 'soil blocks' that are more widely used by growers for certain key crops. Furthermore, few organic solutions exist, despite this being a growing market sector.This project will therefore develop organic, peat-free growing media suitable for producing blocks that can be handled by existing machinery at both the plant nursery stage and during transplanting into the field. However, the findings will also be relevant for conventional production as the basic problem of ensuring the integrity of the blocks from sowing until transplanting is the same.The project will investigate a range of potential materials, concentrating on materials available in the UK to provide a resilient, locally-based solution. The selection of test materials will be made following a literature review and assessment of the 'state of the art' through consultation with growing media industry representatives. Investigations will ensure that the media hold together throughout the whole process of pressing, seeding, seedling growth, transport, and planting in the field. To build on the measurements made of the properties of particular blends a computer model will be developed to quantify the effect of the various ingredients. The most successful media will be identified for subsequent testing by Delfland Nurseries.Delfland will evaluate the performance of selected growing media blends, in comparison with a peat based control, using commercial scale equipment and facilities. Replicated trials will assess the growth and quality of test crops of lettuce transplants. The plant transplants from these trials will be further evaluated after planting out by Riverford Organic Farmers, on certified-organic land and using farm scale equipment to determine the robustness of blocks and the effect of the media on crop yield and quality.Finally, to determine economic viability of the novel peat-free growing media a farm-business cost-benefit analysis will be conducted using partial budgeting methodology to consider all relevant stages of the bio/eco-economy supply chain. The wider environmental effects of each of the proposed materials and blends will be quantified.