Comparison of the effectiveness of digestate and mineral fertilisers on yields and quality of kohlrabi (Brassica oleracea, L.)

Abstract

In a one-year vegetation pot experiment we compared the effect of the digestate from a biogas station and mineral fertilisers on yield and quality parameters of kohlrabi, variety Seguza. Four treatments were used in the trial: 1) untreated control, 2) urea, 3) digestate, 4) urea, triple super phosphate, KCl, MgSO4. The rate of N was the same in treatments 2–4, 1.5 g N/pot. In treatment 4 the rate of P, K and Mg corresponded with the rate of these nutrients in the digestate treatment (3). The weight of single bulbs of the control unfertilised treatment were significantly the lowest (22.9%), as well as the nitrate (6.0%) and ascorbic acid content (66.2%) compared to the urea treatment (100%) and the other fertilised treatments. After the application of the digestate (treatment 3) and mineral fertilisers (treatment 4) the weight of single bulbs significantly increased by 27.9 and 29.2%, respectively, compared to the urea treatment (2). The content of ascorbic acid in the fertilised treatments did not differ (772–789 mg/kg) but it increased significantly compared to the unfertilised treatment (511 mg/kg). There were no significant differences between the two treatments fertilised with mineral fertilisers in the bulb nitrate content (678 and 641 mg NO3−/kg fresh matter, respectively). After digestate application their contents decreased significantly to 228 mg NO3−/kg fresh matter. Digestate treatment resulted in comparable or better yield and qualitative parameters compared to treatment with mineral fertilisers.

Keywords

• digestate
• urea
• mineral fertilisers
• kohlrabi
• yields
• ascorbic acid