Magnesium (often confused with Manganese, a minor nutrient) is an essential element of chlorophyll. A deficiency generally appears as yellowing leaves. Affected carrots may be poor in flavor and color, and tops die prematurely.
When Calcium and Magnesium levels are not in balance, the availability of many other nutrients is affected adversely. Minor nutrients generally produce best results when the Calcium/Magnesium ratio is close to 68:12.
Magnesium deficiency in tomato: Yellowing tissue between veins in older leaves