Iron is essential for all plants, but the Prairie crops most susceptible to iron deficiency are alfalfa, barley, rye and turf. Iron helps in the development and function of chlorophyll. It contributes to the process through which the crop fixes nitrogen from the soil. Plant respiration and metabolism require iron. And iron, like most micronutrients, is part of the makeup of plant enzymes and proteins.
Iron deficiency — sometimes called lime-induced chlorosis — can be seen early in plants, usually in one localized area of the plant. Young leaves will yellow between the veins with the veins staying green. Young leaves are affected first due to the low mobility of iron in the plant. In severe cases, veins will turn yellow as well.
As the growing season continues, yellowed areas will start to bleach, turning from yellow to white. Eventually the bleached areas will start to show necrotic spots.
When a plant is recovering from iron deficiency, veins will return to green first and the rest of the plant from there.
Iron deficiency can result if a soil has a large amount of other heavy metals in it such as copper. Iron is another nutrient that is more readily available in low pH (acidic) soils and less available in basic soil. Iron becomes less available when soils become waterlogged, compacted or poorly aerated.
Organic matter can play a part in iron deficiency. Organic matter is able to create different complexes of iron such as ferrous iron and ferric iron. Iron sulphate is easily available to plants and is one of the best types of iron to correct a deficiency. Without organic matter, these complexes are not present in the soil, taking away from the plant-availability of this micronutrient.
High soil phosphorus can inhibit a plant’s availability to take up iron in the soil. Application of NO3-N can also inhibit iron uptake.
Iron works in a symbiotic relationship with manganese, potassium and zinc. In soils with low zinc content, iron is more easily accessible. High zinc content inhibits iron uptake. Iron and manganese have the same type of relationship. Low levels of potasium have also shown an increase in iron uptake. Saline and more alkaline conditions are positive conditions for iron uptake.
HOW TO APPLY IRON
Iron is best applied in a foliar method. Soil applications have not been found effective. Iron chelates are the best form, but this may only work for small deficiencies since applying five to 10 pounds of metallic iron in a foliar method is uneconomical. Iron chelates incorporate well and are more able to tank mix than other forms of iron. However one must be careful since iron chelates can cause leaf burn if over-applied.
The most effective method to correct an iron deficiency seems to be a two per cent iron sulphate solution applied between 15 and 30 gallons an acre. You can make this solution by mixing 16 pounds iron sulphate to 100 gallons of water and surfactant. This application must occur within 15 days of crop emergence and be repeated every 10 days to two weeks until the symptoms go away for the best results and possible yield recovery. It is important not to over apply iron as it can cause leaf burn if applied to heavy.
Manure applied at 15 to 20 tons per acre can correct deficiency. Also trying to lower the pH of the soil can also help. Lowing soil pH is time-consuming and costly, but it can be done by spreading and incorporating large amounts of material such as gypsum into the soil. This really has not been a viable option because of the magnitude of product needed. Though the same type of soil test used for zinc can be used for iron, it may seem uneconomical to some unless the problem is severe. The best way to check for iron deficiency is to look at the crop for deficiency symptoms.
Jay Peterson farms near Frontier, Sask.