Pea response to foliar application of potassium iodide in North-Western Russia

Agricultural production under conditions of a geochemical anomaly of iodine deficiency poses a threat to human health in Northwest Russia and the productivity of regional livestock farming. A comprehensive evaluation of foliar fertilization of peas with potassium iodide (KI) solution was conducted in a long-term stationary microfield experiment conducted from 2020 to 2024 in the Pskov Region within a vegetable crop rotation system. The experimental soil was a well-cultivated agrosoddy-podzolic light loamy soil with very low total (790 μg/kg) and mobile (6 μg/kg) iodine content. The experimental design included four variants: control (no fertilization), single, double, and triple spraying of peas of the ‘Rocket’ cultivar with a 0.02% KI solution. It has been established that the crop response to iodine fertilization and the level of iodine accumulation in the main and by-products are determined by the specific weather and climate conditions and the frequency of its implementation. Against the background of drought during pea branching phase (hydrothermal coefficient was 0.4–0.8) the grain and straw yield increase grew significantly and reached 109–193 g/m 2 (35–48 %) and 169–612 g/m 2 (35–82 %), respectively. On average, over the five years of the study, crop productivity under the influence of iodine increased by 23 % (from 0.65 to 0.80 grain units), and the iodine content in grain rose 5.4 and 6.5 times – up to 300 and 467 μg/kg, respectively. The optimal fertilization frequency was 3 sprays. This resulted in a 30 % increase in grain yield (from 416 to 541 g/m 2 ) and a 34 % increase in straw yield (from 958 to 1280 g/m 2 ), while the return on investment per gram of iodine reached 14.9 grain units. The iodine content in the grain and straw of the field pea increased by 6.9 and 8.5 times, respectively, compared to the control (from 56 and 72 to 389 and 612 μg/kg).