Gypsum can help remediate iron chlorosis.
Iron chlorosis is a yellowing of plant leaves caused by iron deficiency. However it is not always a true iron deficiency but rather an iron tie-up in plants and soil. Yellow leaves indicate a lack of chlorophyll, the green pigment responsible for photosynthesis (sugar production) in plants.
The causes of iron chlorosis are complex and not completely understood. It could be a deficiency in the soil or the plant or an iron tie-up in the soil or plant. Many reactions govern iron availability and make iron chemistry in the soil complex. Iron chlorosis generally occurs in calcareous soils with a high pH. Even though these soils have plenty of iron, the high pH causes chemical reactions that make the iron unavailable to plant roots
Plants that are native to high pH soils don’t illustrate symptoms of iron chlorosis, because they have evolved to use iron efficiently and can obtain iron from the soil. Recent research has discovered that bicarbonates (HCO3) play a major role since they are readily produced in high pH soils, especially when moist conditions limit iron availability. Even in alkaline soils, bicarbonate is much higher in the calcareous soil than in the non-calcareous soil.
In calcareous soils, bicarbonate inhibits mobilization of accumulated irons from roots to foliage and affects availability of iron in the soil by buffering soil pH. When high bicarbonate irrigation water is applied, iron deficiency is enhanced because bicarbonate is supplied to the soil. The adverse effects of high bicarbonate levels are exacerbated in saturated soils, very dry soils, or compacted soils, where bicarbonate levels increase, leading to diminished root growth and nutrient uptake.
Gypsum reacts with bicarbonate to form calcium carbonate (CaCO3 ,or lime) decreasing the amount of bicarbonate in the soil that affects iron uptake and iron availability.
Plants native to high pH soils are naturally adapted to avoid the symptoms of iron chlorosis, a common issue in alkaline soils. Over time, these plants have evolved mechanisms to use iron efficiently and are capable of extracting it from the soil. Recent studies, however, have shed light on the critical role that bicarbonates (HCO3) play in iron availability in high pH soils. Bicarbonates are more readily produced in moist, alkaline soils, where they limit the availability of iron, especially when the soil is saturated. Interestingly, calcareous soils—those rich in calcium carbonate—have significantly higher levels of bicarbonate than non-calcareous soils, which further impacts the plant’s ability to access the iron it needs for healthy growth.
In calcareous soils, the presence of bicarbonate significantly impacts iron mobility, preventing the efficient transport of iron from the roots to the foliage. This results in a decreased availability of iron, exacerbating iron deficiency symptoms in plants. Moreover, bicarbonate plays a role in buffering the soil’s pH, which makes it more difficult for iron to become available to the plant. The issue is further amplified when high bicarbonate irrigation water is used, as it increases the bicarbonate levels in the soil, leading to a heightened risk of iron deficiency. The situation worsens in saturated soils, compacted soils, or very dry soils, where bicarbonate levels are more concentrated, reducing root growth and nutrient uptake, ultimately stunting plant development.
One effective way to mitigate the negative impact of bicarbonates on iron availability is through the use of gypsum. Gypsum reacts with bicarbonate to form calcium carbonate (CaCO3, or lime), which reduces the bicarbonate concentration in the soil. By lowering the amount of bicarbonate, gypsum can help improve the soil’s pH balance and, in turn, enhance the uptake of iron by plant roots. This process makes gypsum an invaluable tool in addressing iron deficiency, particularly in soils where high bicarbonate levels hinder nutrient availability. Through this reaction, gypsum not only aids in correcting pH imbalances but also promotes healthier, more productive crops by ensuring adequate iron levels for plant growth.
Dr. Davidson posts articles on soil management and subjects to gypsum. If you have suggestions for topics or questions, feel free to contact him at [email protected] or call 402-649-5919.
