Boron (B) is necessary for plants during all vegetation period. Boron is immobile in plants, so the condition of plants is determined by the fact whether they constantly get this trace element. Molybdenum has a positive effect on growth of cereals and row crops. For normal growth leguminous plants require more molybdenum than other plants. In leguminous roots, nitrogen-fixing bacteria use molybdenum for the process of nitrogen fixation from the air. Boron and molybdenum complex as a nutrient improves immune system of plants. Plants need boron and molybdenum throughout all vegetation, they cannot be replaced by other elements. Drought, insufficient moisture, low temperatures, high rainfall in a short time are the factors causing boron deficiency. Boron deficiency appears due to imbalance of boron and calcium as well as due to low content of organic substances in the soil. Calcium inhibits the absorption of boron in alkaline soils.