Magnesium sulfate deficiency can easily occur in both soil and hydroponically grown tomato plants.
Mg deficiency symptoms (interveinal chlorosis on the older leaves) can be an indication of some type of plant stress due either to low or high moisture or temperature conditions. A severe Mg deficiency can result in BER in the fruit. The deficiency primarily occurs when there is an imbalance among the other major elements, K and Ca, plus NH4 as Mg is the least competitive cation among these three. Some tomato cultivars are sensitive to Mg and will easily show deficiency symptoms on their mature leaves, even though Mg may be at a sufficient concentration in the rooting medium.
Under normal soil conditions, Fe deficiency is not likely to occur unless the soil is low in “available” Fe or above 7.0 in pH.
Ferrous deficiency symptoms (light green to yellow leaves occurring on emerging leaves) occur when the plant is under stress from lack of adequate moisture, during periods of rapid plant growth, or changing light conditions.
Normally with time, these deficient-looking leaves will eventually develop a normal green color. Maintaining sufficient Fe concentration in a nutrient solution can be difficult when using various inorganic forms of Fe, such as ferrous sulfate or ferrous ammonium sulfate as recommended in Hoagland-type formulations. Ferrous-deficient plants will respond to foliarly-applied ferrous sulfate solutions.
Tomato plants can be Zn deficient without visual symptoms appearing, resulting in slowed plant growth and poor fruit set.
In both soil and hydroponic growing situations, high levels of “available” P can significantly reduce Zn uptake by the plant. For hydroponic nutrient solutions, keeping the P in solution between 15 and 25 mg P/L (ppm), and doubling the zinc sulfate formulation concentration is needed to avoid Zn deficiency.