Use of gorse compost as growing media in organic agriculture

Resumo

Whether alone or in mixtures, peat is the substrate most commonly used in horticulture to grow seedlings and soilless plants, but quality peat is a scarce resource in southern Europe. In addition peat is a very slowly renewable natural resource so environmental pressure against its extraction has risen. Green compost has an important role to play in peat replacement and the transition to sustainable growing media. But most users have never had confidence in its use or have it dented through past use of poor quality compost. Therefore, quality assurance is key to promote the inclusion of compost in substrates and progress in reducing the use of peat. In this work, it was obtained gorse (Ulex europaeus L.) compost to be used as peat-alternative in organic agriculture. Gorse now occupies large areas and is considered a highly invasive species, so its collection and transformation in growing media would reduce the environmental impact of agricultural activities and would lower the risk of forest fires. The shrubs, consisting mainly of 4-5 year´s old gorse plants, were collected and composted attending two factors: the addition of 5% v/v of poultry manure and the previous irrigation of stacks. The resulted composts were physical, chemical and biologically characterized to be used as substrate and according the requirements for award of the European Union eco-label. Gorse composts were assed as a growing media for organic strawberry container production focusing on its capacity to supply nutrients along the crop cycle and the requirements for additional fertilization. The natural suppressiveness against Fusarium circinatum in P. radiata seedlings of different gorse composts was evaluated too; as well as the effect of Trichoderma asperellum strain T34 as biological control. All composts obtained were mature, stable and pathogen-free. All of them were suitable for use as growing media, exhibiting a high aeration and drainage capacity, little water retention and adequate level of available nutrients. They all fulfilled the requirements of the Community eco-label except for the content in weed seeds in some of them. The addition of poultry manure resulted in substantial changes in the properties of the substrates, which showed higher content in soluble elements and an increased salinity, but this difference was not so much evident during strawberry crop in terms of fruit production or growth. Gorse compost produced on a large scale exhibited natural suppressive properties against Fusarium circinatum disease and inoculation with Trichoderma asperellum strain T34 reduced pre- and post-emergence of disease incidence.