Content of macronutrients and values of mole ratios in leaves of the woolly foxglove (Digitalis lanata Ehrh.) cultivated under differentiated mineral fertilisation

Abstract

The Woolly Foxglove (Digitalis lanata) is one of the herbal plants cultivated in Poland. It is grown as important plant material for production of cardenolides used in the pharmaceutical industry. The aim of the research has been to determine the chemical composition and mole ratios in leaves of cv. Victoria Woolly Foxglove affected by mineral fertilisation. For this purpose, a strict, one-factor, micro-plot field experiment was set up in randomised blocks with four replications. The experimental factor was NPK mineral fertilisation applied to soil in the following doses per hectare. A 0 – no mineral fertilisation, A 1 – 40 kg N + 17.48 kg P + 49.8 kg K, A 2 – 80 kg N + 34.96 kg P + 99.6 kg K, A 3 – 120 kg N + 52.44 kg P + 149.4 kg K. For chemical analyses, samples of 0.50 kg of leaves were taken from each plot. Dried, melted and wet mineralised in sulphuric(VI) acid, the samples were analysed and concentrations of the following elements were determined: nitrogen by Kjeldahl method, total phosphorus by the colorimetric method with ammonium molybdate, potassium, calcium and sodium by flame photometry, and magnesium by atomic absorption spectrometry (AAS). Mole ratios of the chemical elements in leaves were also calculated. In general, the use of mineral fertilisation induced a significant increase in the content of total nitrogen, total phosphorus and potassium, but reduced the sodium concentration in leaves of the Woolly Foxglove compared to the control. After the applied fertilisation doses, the K:Ca and K:Na ratios in leaves were significantly broadened and the Ca:P ratio was narrowed. Significantly higher values of the K:(Ca + Mg) ratio were observed in leaves after applying the medium (A2) and highest NPK ha –1 (A3) doses. The Ca:Mg ratio in leaves of the Woolly Foxglove was distinctly narrowed versus the control after using the