Digestate is equal or a better alternative to mineral fertilization of kohlrabi

Abstract

In a one-year vegetation pot experiment, we compared the effect of digestate from a biogas station and mineral fertilisers on yield and quality parameters of kohlrabi, variety Segura F1. Four treatments were used in the trial: 1) untreated control, 2) urea, 3) digestate, 4) urea, triple super phosphate, KCl, MgSO4. The N dose was the same in treatments 2–4, 1.5 g N/pot. In treatment 4 the P, K and Mg doses corresponded to those supplied in the digestate treatment (3). The weight of single kohlrabi bulbs in the unfertilised control was significantly lower (36.2%) than in the urea treatment (100%) and the other fertilised treatments. After application of digestate (treatment 3) and mineral fertilisers (treatment 4), the weight of single bulbs significantly increased by 36.2 and 33.6%, respectively, compared with the urea treatment (2). The content of ascorbic acid did not differ between the fertilised treatments (282–301 mg/kg), but was significantly lower than in the unfertilised control (334 mg/kg). There were significant differences between all fertilised treatments (2, 3, 4) in bulb nitrate content (745, 187, 462 mg NO3−/kg fresh matter, respectively). After digestate application the content decreased significantly, to 187 mg NO3−/kg fresh matter. The soil Nmin content after harvest varied between 4.19–5.79 mg/kg in all fertilised treatments and the N-NH4+ form prevailed over N-NO3− only in the digestate treatment (3.45/2.34 mg/kg). We recommend the use of digestate to kohlrabi as it results in comparable or better yield and qualitative parameters of kohlrabi compared with mineral fertilizers.