Iron Nutrition in Plants...
We live in a part of the country that suffers from iron deficiency which may cause minor damage in some plants, yet are devastating to other plants. Iron is sometimes present in the soil, but its availability to plants may be low.
Although most of the iron on the earth is in the form of Fe3+, the Fe2+ form is physiologically more significant for plants. This form is relatively soluble, but is readily oxidized to Fe3+, which then precipitates.
Fe3+ is insoluble in the high pH soils of the Treasure Valley, making iron unavailable to plants in our alkaline and often calcium rich soils. Furthermore, in this type of soil, iron readily combines with phosphates, carbonates, calcium, magnesium and hydroxide ions.
When iron deficiency is identified, it can be treated short term by applying a foliar spray such as Ferti-lome “Chelated Iron”, but the best course of action is of course prevention. Therefore, a gardener should identify the real cause of the deficiency and treat it in order to slow the problem in the future. There are several factors that cause alkalinity, which is often a factor in the iron deficiency process. Rain is one of the factors we have no control over and our rain is typically at or near the neutral pH process.
Often, iron deficiency does not indicate insufficient iron supply. It may also be related to other conditions that may affect iron availability. For example: carbonate levels in the soil, salinity, soil moisture, low temperatures, concentration of other elements such as competitive microelements, phosphorus or calcium.
Evaluating these factors and correcting them may save you money that would be spent on ineffective or unnecessary iron applications.
Iron can be applied as a ferrous sulfate or in a chelated form as mentioned earlier.
Ferrous sulfates contain approximately 15% iron. This form of iron is inexpensive and is mainly used for foliar spraying. Applied to soil, it is often ineffective, especially when the pH of the soil is above 7.0 since this form of iron quickly transforms to Fe3+ and precipitates as one of the iron oxides.
Iron chelates are compounds that stabilize metal ions and protect them from oxidation and precipitation.
Chelates hold iron ions in different strengths at different pH levels. They also defer in their susceptibility to iron replacement by competitive ions. In our area where high concentrations of calcium are present, they may replace chelated metal ions.
In our alkaline soil, it is extremely difficult to effectively decrease pH levels and keep them at or near the 6.0 pH level, it is advised to use more stable iron chelates such as those found in Hi-Yield “IronPlus Soil Acidifier”.