Influence of Iodine Fertilization and Soil Application of Sucrose on the Effectiveness of Iodine Biofortification, Yield, Nitrogen Metabolism and Biological Quality of Spinach

Iodine biofortification of vegetables can become an alternative (to iodized salt) method of introducing this element into human diet. Development of agronomic rules concerning its application requires detailed evaluation of iodine influence on plant physiological and biological processes including mineral nutrition and quality of yield. The aim of the study was to determine the effect of iodine and soil application of sucrose on iodine biofortification and nutritional quality of spinach plants. In 2009–2010, a pot experiment was carried out with spinach Spinacia oleracea L. ‘Olbrzym Zimowy’ cv. cultivation on mineral soil. The research included diverse combinations with pre-sowing iodine fertilization (in the form of KI) and soil application of sucrose: 1) – control (without iodine fertilization and sucrose application), 2) – 1 mg I dm of soil, 3) – 2 mg I dm of soil, 4) – 1 mg I + 1 g sucrose dm of soil and 5) – 2 mg I + 1 g sucrose dm of soil. In all tested combinations with iodine fertilization as well as simultaneous application of iodine and sucrose a significant increase in iodine, N-total and soluble oxalate content was observed along with reduced level of nitrate(V) and dry matter in spinach leaves (when compared to the control). The highest accumulation of iodine was noted in leaves of plants treated with 2 mg I + 1 g sucrose dm. Simultaneous application of iodine and sucrose diminished free amino acid content in comparison to the control. Additional introduction of sucrose along with both iodine doses decreased nitrate(V) and N-total level in spinach plants. Soil fertilization with both doses of iodine (1 and 2 mg I dm of soil) applied individually or together with sucrose did not significantly affect spinach yield and the level of nitrate(III), phenolic compounds and soluble sugars in plants as well as iodine content in soil after cultivation.