Soil Nutrient management
Micronutrients
Iron
Plant roots absorb iron from the soil solution most readily as ferrous (Fe2⁺), but in some cases, also as ferric (Fe3⁺) ions. Most of the iron oxides in soil are in the ferric form, which are much less soluble than the ferrous form. Soil pH and the aeration status of the soil determine which form predominates.
Iron deficiency symptoms have stark, defining characteristics and are similar across most crop species. Iron deficiency causes chlorosis, usually first in younger leaves because iron is mostly immobile within plants.
Iron toxicity is primarily pH related and occurs where the soil pH has dropped sufficiently to create an excess of available iron. Excess iron can result in dark green foliage, stunted growth of tops and roots, dark brown to purple leaves on some plants (e.g., bronzing disease of rice).
Acid-loving plants suffer iron shortages when pH rises above 5.0 or 6.0, while many plants become deficient at higher pH. The concentration of iron in the soil solution decreases sharply as the soil pH increases. Calcareous soils can form bicarbonates (HCO3¯) when they are saturated, which can interfere with iron uptake by plants.
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