Micronutrient deficiencies are most likely to occur in sandy soils. If fertilizers containing the basic nutrients N, P, and K are not giving you the desired results, you may need to have your soil tested. Also, in order to make certain nutrients more available to plants, lime may be needed to correct a low pH problem. The only way to know for sure what nutrients your soil is lacking is with a soil test.
Contact your local Cooperative Extension office to learn about proper soil testing procedures.