What are the symptoms of magnesium deficiency in flowers? How to prevent and cure?

The growth of mg-deficient plants was not exuberant. From bottom to top, the old leaves gradually turn green and white from the edge of the leaves to the center, and there are various spots on the veins, and finally the whole leaves turn yellow. The prevention and treatment method was sprayed with 0.20% 0.40% magnesium sulfate aqueous solution for 3 consecutive times, each time at an interval of 7 to 10 days. Soils with severe magnesium deficiency were mixed with 5-10 kg magnesium sulfate per mu and mixed with base fertilizer in autumn or winter.