compared with nitrogen, phosphorus and potassium, silicon, calcium, magnesium and sulfur are included in the middle elements. the content of zinc, boron, manganese, molybdenum, copper, iron and chlorine in plants is 0.1%-0.5%. the other seven elements belong to trace elements, such as zinc, boron, manganese, molybdenum, copper, iron and chlorine.
the role of a large number of elements is necessary for crops, and trace elements are paid more attention to. however, we can not ignore the role of medium elements in the growth and development of crops.
most of the medium elements are enzymes or coenzymes that promote photosynthesis, respiration and substance transformation in plants. they are very active in plants. when crops lack any medium element, growth and development will be inhibited, resulting in yield reduction and quality decline, and even serious crop failure.
the role of moderate elements:
when crops are short of silicon, the toughness of stems and stalks is poor, and they are easy to lodge and be eroded by pathogens. the number of panicles with silicon deficiency decreases in early growth stage, while the number of grains per panicle decreases in late growth stage.
silicon can increase the yield of cereal crops. rice is a silicon-loving crop. silicon fertilizer can improve rice maturity and disease resistance.
silicon can enhance the resistance of crops to pests and diseases, reduce the harm of pests and diseases, improve the lodging resistance of crops, enhance the aeration ability of crops, improve the stress resistance of crops, improve the availability of soil phosphorus, improve the quality of agricultural products, and facilitate storage and transportation.
when calcium deficiency occurs, plant growth is hindered, internodes are shorter, shorter than normal, and tissues are soft; top buds, lateral buds, root tips and other tissues of plants are prone to decay and death, young leaves are curly deformed, or yellow and necrotic from the leaf margin; fruit growth and development is poor.
calcium can reduce fruit absorption, increase fruit firmness, make fruit storable, reduce decay, and increase the content of vitamin c. generally, legumes, beets, cabbage and other plants need more calcium.
when mg deficiency occurs, the plant is short and grows slowly. first, it loses green between veins, while the leaves remain green. later, the green part gradually changes from light green to yellow or white, and brown, purple-red spots and stripes of different sizes appear. symptoms first appear in the old leaves, especially at the tip of the old leaves.
magnesium can promote plant photosynthesis, promote protein synthesis, improve crop yield and improve the quality of agricultural products. rice, peanut, sesame, citrus, banana, pineapple, potatoes and tomatoes in tobacco and vegetables all need more magnesium.
under sulfur deficiency, crop growth is seriously hindered. the plants are short and thin, the leaves turn green or yellow, the stems are thin and rigid, and the tiller branches are few. it is similar to nitrogen deficiency, but the symptoms of sulfur deficiency first appear from young leaves.
sulphur can increase protein content, improve the quality of feed and cereal crops, increase vitamin a content and oil content of oil crops, improve the quality of fruits and vegetables, and enhance the cold and drought resistance of crops.
crops such as cruciferae, liliaceae and leguminosae need more sulfur, while gramineae needs less sulfur.