Evaluating Compost from Digestate as a Peat Substitute in Nursery for Olive and Hazelnut Trees

This study deals jointly with three aspects of environmental, agricultural and energy sustainability: (a) Biogas is a booming energy source worldwide, resulting in an increasing production of digestate, its main by-product; (b) The extraction of peat, mainly used for nursery substrates, is being banned due to the destruction of natural habitats and release of GHGs; (c) Compost can represent a replacement of peat and contributes to the containment of GHGs. This study has verified how a compost obtained from digestate can be used as a substitute for peat in the nursery sector. While previous studies have evaluated compost use on just one species at a time, this study compared the same compost on two very different species: olive tree and hazelnut tree, both with growing interest for new tree plantings. Two concentrations of compost in the potting substrate of nursery seedlings were evaluated: 30% and 45% by weight, measuring the effect on some growth parameters during the growing season. The trials showed responses positive for olive and substantially negative for hazelnut: olive trees manifested better growth parameters with 45% compost, as opposed to hazelnut, where the addition of 45% compost worsened all growth parameters. A general conclusion can be drawn: in the nursery sector, compost can be used to replace peat, but this replacement can almost never be 100 percent, having instead to calibrate the percentage of replacement according to the characteristics of the compost and the individual edaphic needs of the plant species.