Use of solid phase of digestate for production of growing horticultural substrates

Solid phase of digestate (SD) of agricultural biogas plants, containing undecomposed fibrous fractions of organic matter, is usable as a constituent of growing substrates. The content of soluble salts and available nutrients is limiting for SD addition into growing substrates. For addition of SD with initial 80% moisture its content of ammonium nitrogen and available potassium is limiting. The SD with natural moistness can be used in peat based substrates up to 10% volume. The content of ammonium nitrogen during the drying of SD with the use of waste heat from biogas plants is decreased. Optimal proportion of dry SD (dSD) in peat based substrates ranged from 20 to 40% volume. Peat based substrates with 20% volume of dSD had suitable physical and chemical (e.g. content of available potassium< 300 mg/l) properties. These dSD-peat growing substrates have been successfully tested in greenhouse experiments with pot plants (Petunia, Impatiens, and Pelargonium). The addition of dSD to peat based substrates increased air capacity and decreased easily available water content. However, the basic fertilization of the dSD-peat growing substrates is necessary to optimize the content of nutrients.