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Symptoms of nutrient deficiencies can surface in late season corn. Diagnosing nutrient deficiencies can help determine the effects of management decisions for the current crop and any adjustments to consider for the next season. Symptoms of late season nutrient deficiency can appear on corn leaves, ears, and stalks.
Even after the best of growing conditions, symptoms of nutrient deficiencies can surface in late season corn. When growing conditions are ideal, especially in a high yielding environment, there may simply not be enough nutrients left in the soil toward the end of the season for corn to reach its maximum possible yield potential. Advanced agronomic traits, breeding, and production practices for new corn products may require a re-evaluation of fertility practices and monitoring of the plant nutrient status to achieve maximum yield potential.
Nitrogen (N) is often the most limiting nutrient in corn fields. Obvious symptoms of severe N deficiency are stunted yellow plants with small ears, indicating that there was not enough N available. However, there can be more subtle symptoms that begin to show up later in the season as the crop runs short of N (Figure 1). These symptoms appear on leaves as a yellow coloration in a V-shaped pattern, starting at the tip and progressing toward the leaf collar. The color becomes more intense as the problem develops and leaves eventually begin to die at the tips. Symptoms first appear on the lower, older corn leaves. The plants can “fire up” with symptoms rapidly moving from the lower to upper leaves with time. This can create weak plants that are vulnerable to stalk rot which could lead to stalk lodging. Four or more green leaves below the ear is considered a rough visual measure of adequate N at silage harvest.
Figure 1. Foliar symptoms of nitrogen deficiency in late season corn.
Potassium (K) deficiency appears as a yellowing, firing, or dying along the tips and edges of the lower leaves (Fig. 2). K deficiency has become more common in recent years, especially in silage fields where corn stalks are removed. Much of the K taken up by the plant is deposited in the stalk, and if residue is removed, higher applications of K fertilizer or livestock manure may be necessary to maintain adequate levels of K in the soil. K may also not be available to plants in high pH soil, even if soil levels are adequate. Plants can be short with weak stalks. Excessive lodging is often an indicator of a K shortage.
Figure 2. Nitrogen deficiency symptoms on lower corn leaves shown on the left, and Potassium deficiency symptoms shown on the right.
Phosphorus (P) deficiency is more noticeable when corn plants are younger, characterized by reddish-purple leaves. Symptoms may not be obvious in late season corn. A shortage of P can cause a delay in the development and maturity of corn. The plant availability of P can also be low in high pH or alkaline soils. Signs of high pH problems include dark green or purple coloring of lower leaves and stems.
Sulfur (S) deficiency generally appears as a yellowing of young leaves and is sometimes confused with N deficiency. Because S is not as easily translocated within the plant, younger leaves show the visual symptoms first. Symptoms can look like a pinstripe suit with a yellow striping pattern on the newest, upper leaves on the plant. Corn can be stunted and delayed in maturity. S deficiency is favored in sandy soils, acid soils low in organic matter, and soils that have a high or low pH. Maintaining a pH range of 5.6 to 7.5 will result in more efficient uptake of nutrients.
Corn ears can provide an indication of nutrient shortages (Figure 3). However, accurate diagnosis is important because other factors can also cause ear abnormalities. Drought, high temperatures, disease and insect damage, and chemical injury can also cause abnormal corn ears, or interact with nutrient imbalances to add to the problem.
Figure 3. Tip dieback as a result of kernel abortion at the ear tip (A), nubbin ears (B), and zipper ears (C) can be an indicator of nitrogen deficiency. Incomplete kernel set (D) due to poor pollination can be an indicator of phosphorus deficiency. Chaffy ears (E) which are light in weight due to poorly filled, shrunken kernels with spaces in between them can be an indicator of potassium deficiency. Photos courtesy of Peter Thomison, The Ohio State University.
Deficiency symptoms may not always be readily apparent, and soil or plant testing should be used in the diagnosis process. Fall is a good time to begin soil testing, and evaluate your current nutrient management program and consider if changes may be necessary for next season.
Sources: Brown, B., Hart, J., Horneck, D., and Moore, A. 2010. Nutrient management for field corn silage and grain in the inland Pacific Northwest. Pacific Northwest Extension Publication 615. http://www.cals.uidaho.edu. Thomison, P and Geyer, A. 2007. Abnormal corn ears ACE-1. Ohio State University. http://agcrops.osu.edu. Web site verified 7/12/2018. 180712112802