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| Figure 4 a-c. Iron chlorosis is commonly associated with calcareous soils and is expressed as interveinal chlorosis, beginning with the younger leaves. |
The need for and some applications of iron fert
Iron Chlorosis
Most Nebraska soils contain adequate amounts of iron for optimal crop performance. In some soils, however, conditions restrict a plant’s use of iron. As a result, iron chlorosis occurs. Iron chlorosis is commonly, but not always, associated with high lime (calcareous) soils. Iron chlorosis can occur on soils that have excess salts and high or excess sodium or that are poorly drained. It may occur even on soils testing high in iron. Soil test iron is considered to be very low when DTPA-Fe is less than 2.5 ppm, and marginal when DTPA-Fe is between 2.5 and 4.5 ppm. Values above 4.5 ppm indicate low probability of iron deficiency.
Iron is relatively immobile in plant tissue, and chlorosis conditions are more likely on younger tissue. Iron chlorosis causes the interveinal areas of young leaves to become pale green to yellow or white ( Figure 4 a-c ). The interveinal striping on corn and sorghum leaves occurs along the full length of the leaf.
Correcting iron chlorosis is difficult. Manure application is effective when iron chlorosis is due to low soil iron availability, but it may not be effective when soil iron availability is adequate and metabolic use of plant iron is restricted. Mapping of chlorotic areas is recommended for site-specific application of fertilizer iron. Broadcast application of non-chelated iron is generally ineffective as iron rapidly becomes unavailable.
Soybean chlorosis can be managed by planting tolerant varieties, planting at a density of 12 viable seeds per foot, applying iron-chelate fertilizers with the seed, and using a foliar treatment. If chlorosis is a problem, do not plant soybean in narrow rows as it is important to have a high plant density within rows. Applying chelated iron (FeEDDHA), mixed in 5 to 8 gallons of water per acre, directly with the seed is often an effective fertilizer treatment for soybean. Seed dressing with iron EDDHA at 0.2 lb/ac iron has been as effective as applying 50 lb/ac iron as iron sulfate. Soybean yield response to foliar application of iron fertilizer has been inconsistent and generally less effective than applying chelated iron with the seed.
For corn, research suggests that applying iron sulfate (FeSO 4 •7H 2 O) in the seed furrow at rates of 50 to 100 lb of product per acre prevents chlorosis . Iron sulfate (50 or 100 lb per acre depending on chlorosis severity) applied in the seed row was less expensive but of similar effectiveness when compared to chelated iron, especially on non-tolerant hybrids. Corn hybrid selection is important for iron chlorosis management. Avoid over-irrigating high sodium and calcareous soils.
For dry beans, research shows that 1 to 1.5 pounds of FeEDDHA can increase yields in chlorotic areas. The material can be seed applied in 5 to 7 gallons of water with the seed or banded (due to mobility) or can be included in 10-34-0 and banded beside the seed. The FeEDDHA is usually dissolved in 3 to 4 gallons of water, which is then added to the 10-34-0 to facilitate mixing.
Foliar applications of iron can be used for corn, sorghum, soybeans, and dry beans, and have been more effective on hybrids/varieties relatively tolerant of iron chlorosis. By the time most iron chlorosis occurs and is treated with foliar application, significant growth reduction and loss of yield potential have already occurred. To avoid serious yield reductions, make the first foliar application of iron chelate (1 pound of FeEDDHA in 20 gallons of water) or a 1.0 percent to 1.5 percent solution of ferrous sulfate as soon as chlorosis appears. Because so little plant area is covered when the plants are small, repeated spraying every 7 to 14 days is necessary. Spray in early morning or early evening to avoid leaf burning.
