The effect of fertilisation with digestate on kohlrabi yields and quality

Three treatments were used in a two-year (2014-2015) vegetation pot experiment with kohlrabi of the cv. Moravia: (1) untreated control; (2) digestate; (3) digestate + phosphorus (P). The nitrogen (N) rate was the same in treatments 2-3. There were significant differences between years in all parameters. The weight of single kohlrabi bulbs in the unfertilised control was significantly lower in both years (33.1-46.9%) than in the digestate treatment (100%). Digestate supplemented with P (treatment 3) increased the bulb yield significantly by 11.0-14.3% compared with pure digestate (treatment 2). In both years the content of bulb nitrates (mg NO3-/kg FM (fresh matter)) was significantly the lowest in the unfertilised control (135 and 163, respectively). After digestate applications the nitrates content (mg NO3-/kg FM) increased significantly in both years, i.e. to 315-327 (2014) and to 486-509 (2015) compared to unfertilised control. In two years the content of ascorbic acid (mg/kg FM) did not differ among the three treatments (274-288 in 2014 and 311-329 in 2015). Digestates can be recommended for kohlrabi fertilisation prior to planting.