Even after the best of growing conditions, symptoms of nutrient deficiencies can surface in late season corn. Knowing what to look for and the causes of nutrient deficiencies can help you consider what, if any management decisions are necessary for next season.
Symptoms of late season nutrient deficiency can appear on leaves, ears, and stalks. The deficiency symptoms related to the primary macronutrients used by corn plants, nitrogen (N), phosphorus (P), and potassium (K), are outlined below.
Leaves: Firing of and dropping of lower leaves (Figure 1). Late season symptoms appear first on the lower leaves as a yellowing and tissue die off occurring in a V-shaped pattern, starting at the tip and progressing down the midrib of the leaf.
Ears: Tip dieback—poorly filled or unfilled ear tips with little or no kernel development in one of more inches of ear tip; Nubbin ears —small misshapen ears with poor kernel set; Zipper ears—one or more kernel rows are absent that can result in a curved cob.
Stalks: Weakened stalks due to plant cannibalizing stalks to translocate nutrients to feed the ears.
Ears: Deficiency can interfere with pollination and result in poor, incomplete kernel set.
Ears: Lightweight ears with poorly filled, shrunken kernels.
Stalks: Weakened stalks, prone to lodging.
Sometimes, symptoms may not have as great an impact on yield as you might think. For instance, unfilled kernels at the ear tip occur even under excellent growing conditions. Favorable growing conditions can result in a greater than normal number of potential kernels per row, and even if all kernels are not filled, the number filled may still be at or above normal. When ears are consistently filled all the way to the tip, it can actually indicate that planting populations should be pushed higher to optimize yields.3
Are all these symptoms a result of nutrient deficiency? Not necessarily. There can be many causes and sometimes multiple contributors to several of these symptoms. For more information about other causes of abnormal corn ears, see ‘Abnormal Corn Ear Development’ in the Agronomy Library on http://www.channel.com.
There are different ways to investigate whether or not fertility deficiencies caused or may have contributed to a corn symptom. Nutrient deficiencies can occur within the corn plant, due to root uptake issues, or through an actual soil nutrient deficiency. One way to evaluate if the symptom was caused by a nutrient deficiency is by using the end-of-season cornstalk test. The N status of a corn crop can be assessed by measuring nitrate concentrations in the lower portion of cornstalks at the end of the growing season. For further information on this method, as well as assessing the fertility of your soils, see ‘Assessing Nutrient Availability for Corn’ and ‘Keys to Reliable Soil Test Information’ on www.channel.com.
Nutrient deficiencies can result from different environmental and plant factors, such as the nutrient availability to the plant and the plant’s ability to uptake the nutrients.
Moisture Stress. At blister (R2 growth stage), around 75% of the plant’s required N is in the plant and the remainder must still be taken up by plant roots.1 During moisture stress, N uptake through the plant is limited and N must be moved from the leaves to the kernels to compensate. The leaves below the ear are the primary source for N in moisture stressed corn and will be the first to show N deficiency symptoms.
Fertility Level. Research at the University of Illinois determined that many fertility recommendations used today are based on data from previous decades and may not be sufficient for the yield potential of current corn products and management practices.2 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. As corn production and corn yields have increased, a concurrent decrease in soil macro and micronutrient levels has occurred. In 2010, the International Plant Nutrition Institute reported that an increasing number of U.S. soils had dropped to near or below critical levels of P, K, sulfur (S), and Zinc (Zn), indicating that nutrient uptake and removal has not been well matched with fertilizer applications.2 It is recommended that in addition to N, P, and K fertilization, other nutrients should also be monitored to help achieve optimal grain yield potential.
By late in the season, there is nothing that can be done to lessen the impact of nutrient deficiencies. However, it is the perfect time to rate your current nutrient management program and consider if changes may be necessary for next season. The end-of-season cornstalk test can be used to evaluate whether the crop had too much or too little N for optimal yields. Soil testing should also be performed to assess total nutrient availability and indicate whether additional fertilizer is needed to maximize crop growth next season.
1Bly, A. 2013. Evaluating late season corn nitrogen deficiency. iGrow. South Dakota State University Extension. http://igrow.org (verified 9/3/14).2Bender, R., et al. 2012. Nutrient uptake, partitioning, and remobilization in modern, transgenic insect-protected maize hybrids. Agronomy Journal vol 105: 161-170.3Thomison, P. 2010. “Tip dieback” and “zipper ears” in corn. C.O.R.N. Newsletter. http://corn.osu.edu (verified 9/3/14). Blackmer, A.M. and A.P. Mallarino. 1996. Cornstalk testing to evaluate nitrogen management. PM 1584. Iowa State University. Nielsen, R.L. 2011. The “zipper” pattern of poor kernel set in corn. Purdue University Department of Agronomy. www.agry.purdue.edu (verified 9/3/14). Sawyer, J. 2004. Nutrient deficiencies and application injuries in field crops. IPM 42. Iowa State University Extension. Thomison, P. and A. Geyer. 2007. Abnormal Corn Ears ACE-1. Ohio State University. Wiebold, W. 2013. Increased arrested development of corn kernels may have resulted from cloudy weather. Integrated Pest and Crop Management. University of Missouri. http://ipm.missouri.edu (verified 9/3/14). 140828150836