Comparative assessment of Zn accumulation by plants of Silybum marianum depending on fertilizer type

Abstract

Recently, thorny (Silybum marianum) plants have gained considerable popularity in Ukraine. In addition to the proven medicinal properties of this plant for the prevention of human diseases, the use of milk thistle in other areas is increasing. Milk thistle is used as a vegetable plant because its young leaves have nutritional value. It is also grown as a valuable summer honey plant capable of producing honey at 50–70 kg of honey per hectare.Increasingly, there are reports of the introduction of thistle spotted into the modern crop rotation. However, often the technology of growing it has not yet been studied, so traditional technologies are used, which are adapted to regional conditions for the cultivation of spring early crops of a wide-row sowing method. The control of zinc content, like other toxicants, in vegetative mass and seeds of milk thistle, due to insufficient study of this culture, is very rare. This requires further study of the intensity of zinc accumulation in milk thistle plants with modern cultivation technologies that involve the use of a wide range of mineral fertilizers.Field studies were conducted during 2017–2019 on gray medium loam soil in the farms of Vinnytsia region. Sow thistle spotted in spring time using five fertilizer options: applying nitrogen fertilizer ammonium nitrate, phosphorus fertilizer superphosphate is simple, potassium fertilizer potassium chloride, fertilizer mixtures: ammonium nitrate, superphosphate simple, potassium chloride. Based on the results of laboratory analysis of zinc content in leaf mass and seed thistle spotted, the accumulation coefficient was calculated as the ratio of zinc content in the plant to the content of mobile zinc forms in the soil and the hazard ratio as the ratio of zinc content in the plant to MPC.The intensity of zinc accumulation by the leaf mass and seeds of the milk thistle for feeding it with mineral fertilizers was studied. The accumulation coefficient and the hazard coefficient of zinc in the leaf mass and seeds of the milk thistle for feeding it with ammonium nitrate, potassium chloride, and superphosphate were established. It is proved that with the use of fertilizers less zinc is accumulated by the seeds of milk thistle when using a mixture of ammonium nitrate, simple superphosphate and potassium chloride, and leaf mass — potassium chloride. The highest level of zinc accumulation by leaf mass and silybum seeds was observed when fertilizing crops with ammonium nitrate.When using potassium chloride as a fertilizer, the zinc content in the leaf mass of silybum thistle increased by 14.5%, simple superphosphate — by 15.8%, a mixture of ammonium nitrate, simple superphosphate and potassium chloride — by 42.7%, ammonium nitrate — by 81.6%. The use of a mixture of ammonium nitrate, simple superphosphate and potassium chloride causes an increase in the zinc content in the dry matter of the seeds of milk thistle by 11.8% compared to the version without fertilizing. The introduction of simple superphosphate contributes to an increase in zinc content by 17.2%, potassium chloride — by 23.4%, ammonium nitrate — by 26.9%.