Effect of zinc fertilisation on yield and selected qualitative parameters of broccoli

Three treatments were used in two-year (2014–2015) field experiments with broccoli cv. Bejo 2914 F1: (1) untreated control; (2) Zn0.75 – Zinkuran SC as foliar fertiliser at the rate of 0.75 L/ha (375 g Zn/ha); (3) Zn1.50 – Zinkuran SC as foliar fertiliser at the rate of 1.50 L/ha (750 g Zn/ha). The statistically significant differences of individual broccoli parameters were found after zinc applications. In both experimental years the yield of broccoli with additional zinc fertilisation was significantly higher by about 8.2–14.4% (Zn0.75) and 12.5–17.5% (Zn1.50), respectively, than in the control. Foliar zinc application significantly increased the sulforaphane content in broccoli florets by about 19.8–32.9% (Zn0.75) and 37.2–49.3% (Zn1.50), respectively, compared to the control. By contrast, the content of total polyphenolics (of about 9.0–12.5% (Zn0.75) and 33.9–35.2% (Zn1.50)) and antioxidant activity (Zn0.75 (3.7–4.2%) and Zn1.50 (5.3–7.0)) decreased as a result of zinc fertilisation. The investigations pointed to zinc as a very important micronutrient with strong influence on the yield and chosen qualitative, health promoting parameters of broccoli.