Digestate from biogas plants is an attractive alternative to mineral fertilization of kohlrabi

This study examined the potential for the use of digestate from biogas plants for the fertilisation of kohlrabi. Kohlrabi was grown in two pot experiments in consecutive years using digestate, mineral fertiliser (urea) with a nitrogen (N) content equivalent to that in the digestate, mineral fertiliser with N, phosphate (P), potassium (K) and magnesium (Mg) contents equivalent to the digestate, and an unfertilised control. At harvest, the soil receiving the digestate application had higher P, K and Mg contents than the control and the urea treatment. The soil Nmin content was balanced in all fertilised treatments. Soil pH was unaffected by all treatments. Kohlrabi bulbs from the unfertilised control had the lowest weight, nitrate content and ascorbic acid content. Digestate and NPKMg fertiliser treatments increased bulb weight compared with the N-only urea treatment. Ascorbic acid content did not differ between fertilised treatments. There were no differences in bulb nitrate content between the mineral fertiliser treatments, but digestate application gave a low nitrate content. Bulb macroelement contents varied irregularly among treatments.