Trace mineral are also known as micro-nutrients because they are used by the plant in very small amounts. Despite the small amounts needed, deficiencies of these elements can cause big problems in plant health. Some of these mineral are zinc, iron, manganese, copper, boron and molybdenum. Lack of boron can cause a plant to suddenly stop growing. Manganese is necessary for photosynthesis.
Copper is very important in the reproduction process and affects the yield.
Good sources of trace elements are manures, green sand and kelp extracts. Many of the fertilizers mentioned above are available locally at garden centers and health food stores. Soil fertility can be very complex. The best way to check your soil's health is to have it tested and the results properly interpreted. Your local extension office or a private lab can provide this service.