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eturn to table of

eturn to table of contents IRON CHLOROSIS High pH soil conditions can restrict corn’s use of iron, resulting in iron chlorosis. This condition is commonly associated with calcareous soils. Chlorosis can also occur in fields that are poorly drained, high in sodium, and possess excess salts. Soil iron is considered to be very low when it drops below 2.5 ppm. Interveinal striping on corn will cause young leaves to become white, yellow, or pale green. Soils prone to iron chlorosis often readily flocculate and seal over; therefore, aeration of the soil by breaking the seal can improve early plant growth. Manure application can help alleviate low soil iron availability, and mapping areas of deficiency is useful for specific application of fertilizer iron. Iron sulfate can also be applied at rates of 50 to 100 lbs of product per acre (55 to 110 kg/ha) (Wortmann et al., 2013). Foliar applications of iron have also been shown to be successful on corn hybrids relatively tolerant of iron chlorosis. ZINC DEFICIENCIES Corn is highly sensitive to zinc. There is a high probability that the crop will respond positively to applied zinc in the case of low soil zinc availability or if the soil meets any of the following criteria: • Soil possesses a pH greater than 7.3 (calcareous soil). • Erosion has removed the topsoil. • Leveling or terracing has occurred on the land. • Soils are very sandy with low organic matter content. Zinc levels of 0.8 ppm are adequate for crop growth, but if the soil content of zinc drops to 0.4 ppm or less, a zinc application is highly recommended. The first symptoms of zinc deficiency will be on new leaves with interveinal striping ranging from the base to the tip. White or yellow broad bands will occur on either side of the midrib, but the leaf margins and tips will remain green (Figure 4). Corn is a good indicator crop of low soil zinc levels. If the corn crop does not exhibit a need for added zinc, other crops are not likely to need zinc fertilizer. The numerous zinc fertilizer products are broken out into categories of varying components, such as inorganics, synthetic chelates, Figure 4. Corn leaf showing zinc deficiency, characterized by interveinal stripes in the center of the leaf and surrounded by green borders against the broad yellow or white bands. natural compounds, soluble and insoluble products, and other variable sources of zinc. Sources of zinc for fertilization should be chosen on the basis of solubility, cost, ease of application, and residual effects. Soluble sources of zinc are recommended for soils with high pH. PHOSPHORUS DEFICIENCIES Phosphorus is an essential macronutrient for healthy plants as it plays a role in creating plant structural components, biochemical reactions, and photosynthesis. Phosphorus is often less available to the plant in calcareous soils resulting from reactions with calcium. At soil pH levels from 7.2 to 8.5, phosphorus becomes unavailable to plants because it fixes as insoluble calcium phosphates. Phosphorous deficiency is commonly associated with a reddish-purple coloring of corn leaves and stems that can cause stunted or small plants early in the growing season (Figure 5). Purpling of corn may not be the sole indication that the soil is lacking phosphorous. Conduct a soil test to confirm phosphorous and pH levels. For soils testing below 15 ppm, phosphorous fertilizer application is strongly recommended to build up levels available to corn (Wortmann, 2014). Rock phosphate, water soluble phosphate, and dry phosphate are different sources of fertilizer that are available for application. A liquid polyphosphate, however, can have some additional benefits as it can increase the availability of some other micronutrients in the soil. A grower should choose a fertilizer based on the cost of its nutrient content and the moisture content available to dissolve dry fertilizers. Organic sources of phosphorous are also abundantly available in crop residues, which will return to the soil by late fall. Manure is also a source of phosphorus, but nutrient content can vary widely among different manure types. (Always test manure for nutrient composition.) Application methods, such as banding phosphorous fertilizer, can increase fertilizer effectiveness. MANAGEMENT RECOMMENDATIONS General tips to manage high pH include: Figure 5. Corn seedling showing purple color due to phosphorus deficiency. • Aggressive utilization of starter fertilizer • Manure application to areas with known micronutrient issues • Limiting early water applications, if possible, to keep soils from sealing over. (Wet soils also lead to more bicarbonate uptake in the seedling root system, which can effectively block the uptake of other nutrients like phosphorous, iron, and zinc.) HYBRID SELECTION A strong preliminary defense against high soil pH levels is specific hybrid placement: • Select corn hybrids that show optimum yield performance. • Select corn hybrids that can maintain acceptable plant and ear height. • Select corn hybrids that can tolerate elevated soil pH levels • Visit with your local Pioneer sales representative or dealer for information on Pioneer ® brand corn hybrid options. 78

eturn to table of contents CORN SEEDING RATE CONSIDERATIONS by Steve Butzen, Agronomy Information Consultant SUMMARY • Each year, DuPont Pioneer evaluates corn plant population responses in research trials that span the Corn Belt of North America. • Growers can use the multi-year and multi-location results to identify the best potential planting rates specific to their hybrid, location, and management practices. • In studies conducted from 2009 to 2014, the seeding rate that generated the most income ranged from about 31,000 seeds/acre at the 150 bu/acre yield level to over 39,000 seeds/acre at the 240 bu/acre yield level. • According to a 2015 DuPont Pioneer survey regarding seeding rates on corn acres in the U.S. and Canada: »» almost 10% are now planted at 36,000+ seeds/acre »» one-third are planted at 33,000 to 36,000 seeds/acre »» one-third are planted at 30,000 to 33,000 seeds/acre • In challenging emergence environments, growers may need to increase rates. See seeding rate tips in this article or contact your local Pioneer sales professional for help. 79

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