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By Cleo Palmer
The following symptoms are for plants in general and not for irises specifically. It is likely, however, that they would be similar in irises in most cases.
Many of the micronutrients are carried over in the organic matter in the soil, and many soils are becoming deficient in organic matter, resulting in micronutrient deficiencies. Minor plant growth element shortages are the greatest in sand and sand-loam soils, but outright deficiencies are showing up in some clay soils as well.
Nitrogen, phosphorous and potassium are the recognized primary plant growth nutrients.
Calcium, magnesium and sulphur are the identified secondary nutrients. This does not mean that they play a secondary role in growth. They are as important to plant nutrition as are the recognized primary nutrients.
Many plants contain as much sulphur as phosphorous and sometimes more. Secondary nutrient deficiencies can depress plant growth as much as the major nutrient deficiencies.
Calcium in plants stimulates root and leaf development. It forms compounds which are part of cell walls. Poor root growth is one common symptom of calcium deficiency.
Magnesium is a mineral constituent of plant chlorophyll. It is actively involved in photosynthesis. An atom of magnesium, as one example, is at the heart of every chlorophyll molecule. Magnesium also aids in phosphate metabolism, plant respiration and the activation of several enzyme systems within the plant. Magnesium deficiency symptoms usually appear on lower older leaves. It shows as a yellowish-reddish color, while the leaf veins remain green.
Sulphur is essential in forming plant proteins because it is a part of certain amino acids, the building blocks of protein. Sulphur is fairly well distributed throughout the tissues of the plant. Sulphur deficiency shows up as a pale green color in plants, generally appearing first on younger leaves. Leaves tend to shrivel as the deficiency progresses. Leaves die only in extreme cases, although plants can die in the seedling stage. Sulphur deficiency shows up most often in sandy soils low in organic matter in areas of moderate to heavy rainfall.
Organic matter decomposing in the soil influences how much sulphur is available to the living plant. The reduction of some pollutants in the atmosphere has reduced the amount of sulphur once available to plant growth.
Aside from the three secondary plant growth elements (calcium, magnesium, and sulphur) there are seven recognized micro-nutrients needed for plant growth. These are boron, copper, chlorine, iron, magnesium, zinc, and molybdenum. It is widely held that acid soil conditions will reduce the availability of iron, magnesium, boron, copper and zinc.
A key to plant deficiency is the color change in the lower leaves as follows:
Nitrogen: Plants light green -- lower leaves yellow.
Phosphate: Plants dark green -- leaves and plants small.
Potassium: Brown discoloration and scorching along outer margin of lower leaves.
Manganese: Lower leaves have a yellow discoloration between veins. Finally, reddish- purple from edge inward.
Zinc: Pronounced interveinal chlorosis and bronzing of leaves.
Calcium: Emergence of primary leaves delayed. Terminal buds deteriorate. Color change in upper leaves. Terminal bud dies.
Boron: Leaves near growing point yellowed. Growth bud appears as white or light
brown dead tissue. Terminal bud remains alive.
Sulphur: Leaves, including veins, turn pale green to yellow--young leaves first.
Iron: Leaves yellow to almost white; interveinal chlorosis to leaf tip.
Magnesium: Leaves yellowish-gray or reddish-gray with green veins.
Copper: Young leaves uniformly pale yellow--may wilt and wither without chlorosis.
Chlorine: Wilting of upper leaves--then chlorosis.
Molybdenum: Young leaves wilt and die among margins.
(Taken from Region 22 News - Fall 1985 - with thanks)
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