Unmasking Iron Deficiency
When leaves on a plant turn from green to yellow, the blame often gets pointed to nitrogen (N) deficiency, or less often to magnesium (Mg) deficiency. However, many times the real culprit is a lack of iron. Soil tests and tissue tests can fail to show existing iron deficiency within a crop.
Plant-available iron levels are difficult to determine for two reasons. First, iron is easily bound up chemically in the soil when the soil pH is greater than 6.0, and most agronomic crops are grown at ranges between 6.5 and 8.0. Although a soil test will show that iron is present at adequate levels, with higher soil pH values much of the iron present is oxidized in to a form that cannot be absorbed by the plant. Second, iron is relatively immobile inside the plant. When an iron deficiency occurs it happens first in the newer growth. Plants are not able to efficiently pull iron up from older leaves to meet the needs of the crop. “Normally when taking leaves for a tissue test both younger and older leaves are avoided,” says Rick de Jong, International Business Development manager for Agro-K. With NovaCropControl sap analysis both young, fully expanded leaves and old, still viable leaves are collected and separately analyzed, achieving a more complete nutrient picture.
de Jong says he has seen examples across North America where iron levels in the soil are strong but due to nutrient interactions, particularly with phosphorus, the iron is inhibited from coming into the crop.
“We had a really high phosphorus level in the soil and we didn’t connect the dots around the nutrient interactions going on,” de Jong says. “We were thinking nitrogen was a bit low so we that is what we applied when really it should have been iron in the spray tank.”
At Agro-K we are using NovaCropControl Sap Analysis to measure both plant mobile and immobile nutrients. The grower is getting an accurate picture of what nutrition is available to be used by the plant at that point in time. As sap analysis becomes more widely used, iron deficiencies that are being incorrectly interpreted as nitrogen or magnesium deficiencies are being uncovered. Applying nitrogen or magnesium may green up the foliage, but it only masks the underlying issue.
Iron Supports Chlorophyll Production
JP Jacobson, Technical Sales Representative at Agro-K, says “Iron is essential for chlorophyll production. Nitrogen and magnesium have significant roles to play in chlorophyll formation so adding them can make the leaves greener. But it’s not addressing the true issue of the iron deficiency. In fact, by applying these other nutrients, we’re not supporting chlorophyll production as well as we should. We’re making the leaves greener, but we’re tapping the iron lower and lower. We are forcing the plant to do something without providing the food it needs to do it.”
de Jong says he has gone back to growers with a diagnosis of iron deficiency and has been met with surprise. It is easy to see improvement quickly by applying foliar iron. With the Right Form of foliar iron the response is visible in the crop fairly rapidly. Growers will say, ‘My dad used to put foliar iron on all the time. Why did we stop doing that?’”
A Two-Pronged Solution
Because there are two main causes of iron deficiency, a two-pronged solution can be the best approach. In the soil, nutrient chelation is a viable option to maintain iron availability. Chelates are molecules that surround the nutrient with the goal of preventing undesirable chemical reactions that would prevent the nutrient from being plant available. The trick is to balance the ability of the chelate to keep the iron in a desirable form while not “clawing” to the nutrient so strongly as to prevent uptake by the plant.
Several types of chelates exist, and they are more or less effective at different pH levels. EDTA is effective up to pH 6.0, but just 50% of iron remains in solution at pH 6.5. DTPA is excellent up to pH 7.0, but just 40% of iron is still in solution at pH 8.0. EDDHA and its salts, EDDHSA, maintain iron availability to plants past pH 9.01. Using a chelate appropriate for your soil pH range is key.
Agro-K’s Photo-Op 0-0-1 provides liquid chelated iron using EDDHSA chelation to provide maximum iron availability in the soil. It also contains the essential nutrients potassium, sulfur, manganese, and the beneficial nutrient cobalt. Jacobson recommends using it in-furrow at planting or applied in season through fertigation. Ensuring crops have enough iron during periods of maximum vegetative growth, is vital.
Foliar iron in a formulation easily absorbed by plants is the other part of the solution. Agro-K’s Iron Dextro-Lac® 5.5% answers this need by providing iron as a simple sugar (dextrose-lactose) that achieves rapid, efficient nutrient uptake and utilization with little energy expenditure from the plant.
“You get almost 100% uptake within the first 48 to 72 hours after spraying,” de Jong says. “ Agro-K’s Iron Dextro-Lac® 5.5% can rapidly address an immediate iron requirement, reducing negative impacts on yield and crop quality. While, for a longer-term solution, providing iron in a stabilized form in the soil with Photo-Op will support the plant’s ongoing needs. Meeting a crop’s iron requirements is important for the production of chlorophyll and ultimately leaf function.”
1Argo, B., and P. Fisher. Understanding pH Management. Meister Publications, 2002